Mountain Area Forecast ( Jan 31-Feb 2 )

ALERT For Significant Snow Accumulations During Thursday Into Friday – Bitterly Cold Air And Wind Chill Factors Are Expected To Make This A Significant Impact Event In The Mountains

*Many school closings and schedule changes are expected for Friday ( Hey Teachers!!! ).

Significant snowfall is expected during Thursday Night into Friday Morning with a change to snow at all elevations in the 7:00 PM to Midnight period of Thursday evening.

The Potential For A Period Of Snow On SW Upslope Flow Exists For The Locations Indicated Above During Thursday Afternoon Prior To A Change To Snow At All Elevations And Sites Into Thursday Evening

The potential for SW Flow Upslope Snow is being monitored for Thursday in locations along and to the southwest of the orographic lifting zone generated by the High Knob Massif and Tennessee Valley Divide.

Main aspects that could prevent formation of this unique feature of Appalachian Climatology are development of a cross-contour ageostrophic flow that cuts across high terrain to force sinking  air over valleys, instead rising, and stronger warm air advection above 850 MB than models indicate.

Locations inside the RED above will be most favored where low-level air will be forced to rise to highest levels, with areas in the black in the potential zone where air rises 1000 vertical feet or more upon valley floors between the Virginia-Tennessee border and  the City of Norton.

Wednesday Night Into Thursday Morning

Mid-high clouds.  Windy.  SSW-SW winds 10-20 mph, with higher gusts, at elevations below 2700 feet.  SSW-SW winds 15-30 mph, with higher gusts, along mountain ridges above 2700 feet.  Temps varying from 20s in sheltered valleys to the mid-upper 30s.  Wind chills in the 20s and 30s, except locally below 20 degrees in stronger gusts on high peaks.

Thursday Morning Through The Afternoon

Increasing & lowering cloud bases with rain, mix, and snow developing. The chance of snow-mix more likely along and southwest of the High Knob Massif-Tennessee Valley Divide, with mix or rain northeast of this corridor.  SW-WSW winds 5-15 mph, with higher gusts, at elevations below 3000 feet.  SW-W winds at 10-20 mph, with higher gusts, at elevations above 3000 feet.  Temperatures in the upper 20s to low-mid 30s, or falling to these levels, except middle to upper 30s in downslope locations ( coldest at highest elevations ).  Wind chills in the 20s to lower 30s, except in the 10s at the high elevations in the High Knob Massif.

Thursday Night Into Friday Morning

Rain or a mixture changing to snow.  Snow heavy at times.  Turning bitterly cold.  SW to W winds shifting NW at 10-20 mph with higher gusts.  Temperatures plunging into the 10s by morning, with single digits at highest elevations.  Wind chills dropping into the single digits above and below zero, except to under -10 degrees F at highest elevations.  Rime formation at elevations above 3000 feet.

Preliminary Snowfall Forecast ( Into Friday AM )

2″ to 4″ at elevations below 2500 feet

4″ to 8″ at elevations above 2500 feet

Target Snowfall of 4″ for Norton-Wise ( +/- ) 1″ Error Potential.  This suggests a 3″ to 5″ snowfall potential for the Norton-Wise area, with higher amounts likely across the sprawling high country ( above 3000 feet ) in the High Knob Massif.

A potentially more significant winter storm will impact the mountain region this weekend into early next week.

Weather Discussion ( Interesting )

A very interesting, to say the least, weather pattern is now taking shape.  Although the next wave arriving by later this weekend will be much stronger, the disturbance impacting the mountain area Thursday into Friday has potential and will have a notable impact even if the rain-snow change does not occur until after sunset Thursday.

From a research perspective the Thursday system will be very interesting to me and has potential to develop snow on a SW upslope flow.  Although I have documented these SW upslope snowfall events back into the 1970s, I have a composite chart displaying 925 MB flow during a few “younger” events.

If SW upslope flow snow occurs it will only be for part of this event, with the main snow period being Thursday night into Friday morning.  That is generally the case, with only a few events in the past being almost completely dominated by SW upslope flow snowfall.  At the least, this type of flow will keep temperatures colder and make for a faster change to snow in the SW upslope flow corridor versus locations under downslope flow on SW winds.

Recent terrain model forecast trajectories are nearly identical, as noted below, but translating that to reality requires the model to be accurate with both flow trajectories and the magnitude of warm air advection around and above 850 MB.

Looking at new 00z data on Wednesday I think that this is trending toward mostly an all snow event for locations in upper elevations of the High Knob Massif, with snow levels during Thursday afternoon prior to the widespread change into all snow ( at all locations ) being the only real question. Places that get snow during the SW flow period will pick up general 1″-3″ amounts; therefore, I have factored that into my preliminary snowfall forecast for upper elevations.

If snow levels should drop to the floor of Powell Valley prior to the main, widespread change to snow then final snowfall amounts in such locations will tend to be near the top, or above, my current forecast ranges.

Meanwhile, I introduce a new weather station courtesy of one of my field research students, Layton Gardner, who graduated with honors from UVA-Wise in Spring 2017.

Layton is currently assisting with the High Knob Project as he prepares to later attend graduate school.

Layton’s station is less than 2 air miles from Lonesome Pine Airport and is about 100 feet higher in elevation.  It should not be surprising, of course, that the air temperature runs lower ( I have only talked about this now for YEARS ).

At a slightly higher elevation than the Airport cold air drainage can certainly not be blamed, and since Layton’s station has a small solar radiation shield I highlight current data when incoming and any reflected insolation is not a factor ( on a well mixed night ).

A 4 degree F air temperature difference at current recording times ( note 39 degrees at 8:14 PM versus 43 degrees at 8:15 PM ).

Recap Of The January 29-30 Event

A beautiful Great Lakes connection was featured during the January 29-30 event, with orographic mountain waves even visible on this night image from GOES-16.

Snow depths varied from 1″ at UVA-Wise to 3″ at Layton’s station, only a short distance away, with 2″ measured by Superintendent Andrew Greear at the City of Norton’s Water Plant ( 3.81″ of total precipitation in January ).

Snow depths of 3″ to 5″+ were common at upper elevations across the High Knob Massif and Black Mountain, with 3″ being measured at my station in Clintwood.

Mountain Area Forecast ( Jan 29-31 )

ALERT For Moderate To Heavy NW Upslope Flow Snowfall Monday Night Into Mid-Morning Tuesday

A upper air wave and significant moisture transport from the Great Lakes is likely to generate heavy upslope snowfall during Monday Night into Tuesday, especially along & west northwest of the Cumberland Front ( High Knob Massif and Tennessee Valley Divide ).

Locations along the west-northwest side of Clinch Mountain, as well as the secondary lifting zone from Mount Rogers southwest along the Tennessee-North Carolina stateline to the summit level of the Great Smokies are also included; however, the most widespread impacts will occur along and to the northwest of the Cumberland-Allegheny Front.  Reference the end of this page for Mesoscale-Synoptic notes.

Bursts of intense snow are expected to reduce visibility and create hazardous driving conditions Monday Night into the overnight of Tuesday.  Please use extreme caution.

Cold Air Is Expected Tuesday Into Wednesday Morning

Temperatures are currently expected to drop into the 10s to around 20 degrees on Tuesday Morning, with single digits to around 10 degrees at highest elevations.  Wind chills will be significantly lower at mid-upper elevations.

The potential for the coldest temperatures to occur in mountain valleys is being monitored for Tuesday Night into Wednesday AM, with single digits and 10s.  Local below zero readings will again be possible within coldest mountain valleys at upper elevations of the High Knob Massif ( especially if snow is on the ground ).

Sunday Night Into Monday Morning

Periods of Drizzle.  Dense fog at mid-upper elevations above 2000-2500 ft, then cloud bases lifting at upper elevations.  Areas of dense fog possibly developing or reforming at low-middle elevations.  NNW-NNE winds 5-10 mph with higher gusts.  Temperatures dropping into the 20s to around 30 by morning, coldest upper elevations.  Wind chills dropping into the 20s to around 30 degrees, except 10s at highest elevations in gusts.  Freezing fog at the highest elevations into overnight prior to clouds lifting.

Monday Morning Through The Afternoon

Low clouds giving way to a mid-high cloud-sun mix before increasing clouds during late afternoon.  A chance of snow flurries or sprinkles late.  WNW-NW winds 5-15 mph, with higher gusts.  Temperatures varying from upper 20s to low 30s at highest elevations to the upper 30s to lower 40s.  Wind chills in the 20s and 30s, except 10s high peaks.

Snowfall Forecast Through Mid-Morning Tuesday

2″ to 4″ along and north-northwest of the Cumberland Front, with locally higher amounts, especially at upper elevations within the High Knob Massif.  A more narrow zone, along the secondary lifting zone, is expected with similar to somewhat less amounts from Mount Rogers southwest along the TN-NC border to the Smokies.

A dusting up to 1″ in downslope locations along the Powell, Clinch and Holston river valleys ( any bursts here being due to instability aloft and not orographic rise ).

Monday Night Into Mid-Morning Tuesday

Turning colder with snow showers & squalls.  Bursts of intense snow.  NW winds increasing to 10-20 mph, with higher gusts.  Blowing-drifting at high elevations.  Temps dropping into the 10s to lower 20s at low-middle elevations along and northwest of the Cumberland Front, with single digits to low 10s at upper elevations.  Wind chills in the single digits to low 10s, except 0 to -15 below at upper elevations above 3000 feet.  Rime formation at high elevations.  Widespread hazardous travel conditions developing across the upslope zone.

Mid-Morning Tuesday Through Tuesday Afternoon

Snow showers & flurries gradually ending.  Becoming partly to mostly sunny.  Cold.  NW winds 5 to 10 mph with higher gusts.  Temperatures varying from mid-upper 10s to mid-upper 20s to around 30 degrees ( coldest upper elevations ).  Wind chills in the 10s to low 20s, except single digits at highest elevations.

Tuesday Night Into Wednesday Morning

Mostly clear through the evening, then increasing mid-high clouds overnight into morning.  Large vertical temperature spreads developing between frigid mountain valleys and rising temperatures on mountain ridges.  Light & variable winds becoming SSE-SSW at 5-10 mph on ridges.  Temps dropping into single digits & 10s, then rising on mountain ridges into the 20s overnight into morning.  Local below zero temperatures possible in upper elevation valleys.

The potential for more heavy snow is being watched for the February 1-2 period, with additional waves expected to bring more snow by February 4-5 and beyond into next week.  A very snowy period is upcoming for the mountain area.

Weather Discussion ( Very Active )

A very active ( energetic ) winter pattern will be returning to dominate the mountain landscape through coming days.

The initial priority features low cloud bases, drizzle, and dense fog through Sunday Night into Monday on northerly upslope flow and dropping temperatures.

A short break during Monday will feature a dissipation of low clouds as mid-high clouds appear overhead to signal the next weather system rapidly approaching.  An increase in clouds will occur later Monday as bases begin to drop once more on increasing NW upslope flow.

Prime conditions develop Monday Night into Tuesday for snow showers & squalls.  I expect heavy snow with intense bursts of whiteout type snowfall at times to greatly drop visibility and create hazardous driving conditions.

*There are likely to be many school delays and cancellations by Tuesday morning, especially in counties along and west of the Cumberland-Allegheny Front.

Good orographic forcing will be aided by steepening lapse rates and a passing upper wave to really help intensify the snow showers into squalls.  For those unaware, this setting could really catch them off-guard so be warned now if you have travel plans Monday Night into Tuesday Morning.

Albedo will make certain that Tuesday is a cold day with continuation of low sun angles once the snow showers and flurries end and low clouds break.  A rather classic setting follows into Tuesday Night with light winds and a plummet in temperatures over snow cover through the evening, this will be enhanced by warm advection aloft with a strong temperature inversion forming above valleys.

A couple examples, of many, from January 2018 of rapid evening temperature drops analogous to what is expected Tuesday evening in high valleys of the High Knob Massif  are cited here ( with strong drops in all valleys, these just being part of our high country mesonet ).

Reference my 010618 Forecast in the “Previous Discussion” section to review the above period of time as I was forecasting it to occur.  The above data was downloaded during a January 27 Field Trip with research students from UVA-Wise.

At Midnight on January 7 the temp was -8.4 degrees Fahrenheit below zero, with the following regional temperatures reported at the same time courtesy of the WCYB-TV 5 archive.

Beyond Wednesday the main focus will be on upstream waves in the jet stream that will threaten the mountain region with a potential winter storm.  Right now it remains only a potential, but the totality of ensemble guidance from the European group suggests that a threat is justified.  This should become clear by mid-week, so stay tuned.

The following was written Monday afternoon-early evening, then an internet outage prevented posting until near Midnight on January 29.

Mesoscale-Synoptic Forecast Notes – January 29

From my perspective this was the easiest winter forecast of the season, as it was very clear as to the result.  That is far from being true regarding numerous NW flow settings in the southern Appalachians, with the main difficulty being marginal Great Lake air flow trajectories ( which can be calculated in reverse during and after events ).

11:00 PM Update: 2″ to 3″ of snow is on the ground at my official station in Clintwood.  This snow was due to the cold frontal band and upper wave.  Now the Great Lake moisture follows to continue snow into sunrise to mid-morning Tuesday when dry air will surge into the region to dissipate low-level moisture.

Remember, of course, my elevation is 1560 feet above mean sea level or just a bit higher than Tri-City Airport.  The main difference being this location is embedded within the initial lifting zone with respect to NW flow trajectories, the main emphasis of these notes.

It is important to note that my use of terrain features is based upon 30 years of research, during which time the collection of data has demonstrated that the concept of lift should be applied in respect to orographic forcing based on which lifting zone should receive the most emphasis under what atmospheric conditions.

In the middle, bursts of snow, like observed in the Great Valley during this event tend to be dynamically supported via steep lapse rates and/or upper divergence and cyclonic vorticity advection.  Once that departs the Great Valley is subjected to inverse forcing, which from an orographic viewpoint = downsloping to be overly simple.

These notes; however, are about orographic forcing and the primary and secondary lifting zones which it generates and some concepts that forecasters need to apply.

It is generally understood, for example, by forecasters that SE air flow streaming into the Blue Ridge generates heavier precipitation along the Blue Ridge escarpment versus more interior locations along the Blue Ridge ( Mount Mitchell and Grandfather Mountain tend to get more than mountains on a northeast-southwest transect through Mount LeConte on this type of flow, and Meadows of Dan tends to get more than Whitetop Mountain ).

Even through Meadows of Dan is significantly lower in elevation than Whitetop Mountain, the initial lifting of moist air along the flank of the Blue Ridge generates the heaviest precipitation on SE air flow trajectories in the MEAN ( there always can be exceptions during any particular weather event ).  This is also the reason that southwestern North Carolina contains the wettest terrain in the southern-central Appalachians since it is situated in a position to obtain initial lifting of inflow from both the Gulf of Mexico as well as the Atlantic Ocean ( total mean annual precipitation tending to decrease with increasing distance from the zone of initial lift due in large part to increasing moisture extraction by orographics that force repeated rises and sinking of air along a flow trajectory ).

The Blue Ridge ( and especially its escarpment ) is the primary lifting zone with respect to SE flow trajectories.  Leeward sinking generates an enhanced minimum in total precipitation along the Great Valley corridor, followed by an increase in amounts again along the secondary lifting zone of the Cumberland-Allegheny Front on SE flow.

The secondary lifting zone produces less total precip than the primary lifting zone, due in part to mountains being lower in mean elevation but also due to upstream moisture extraction along the primary lifting zone = less total moisture within a vertical column of the atmosphere to be precipitated out ( * ).

*While this is generally true, I have identified a unique winter circulation that appears indigenous to the High Knob Massif which greatly enhances snowfall on SE air flow trajectories under specific conditions.  But that is not what these notes are about.

Flip this to NW flow.  Since NW flow during winter is often cold, only snowfall will be considered.  During NW flow the primary lifting zone is formed by those mountains & their adjacent foothills which are along & west of the southeast flank of the Cumberland-Allegheny Front.

During NW flow the Cumberland-Allegheny Front becomes the focus of the primary orographic lifting, and in the mean the greatest snow amounts with initial lifting ( the towns of Wise and Clintwood, for example, have higher annual snow totals than Big Meadows at the top of Shenandoah National Park even though they are much lower in elevation ).

Shenandoah National Park reports that 43 cm ( 37.0″ ) of snow falls annually in Big Meadows at 3500 feet above mean sea level versus around 112 cm ( 44″ ) at 1560 feet elevation in Clintwood, and up to 196-274 cm ( 77-108″ ) in the 3200-4200 foot elevation zone of the High Knob Massif.  Granted all air flow trajectories comprise mean annual snowfall totals, but a significant amount of the annual tally is comprised of NW flow snow and even more is associated with air flow trajectories having westerly components.

A major, major problem in past decades were models that always tended to “model” heaviest snow toward the ECD, or Eastern Continental Divide, on NW Flow snow and most other flow trajectories ( the ”horseshoe” pattern that now shows up well in modeling around the Great Valley was not present during past decades ).  Although model resolution has improved, it is still lacking in part because elevation remains a controlling factor + models can not understand or parameterize the initial lifting concept with still poor resolution of important complex terrain features ( ** ).

**This remains a major factor for the Cumberland Front more so than the Allegheny Front, since it becomes part of the Eastern Continental Divide at the latitude of central-northern West Virginia + there are many more NWS Cooperative stations at elevations above 3000 feet which are used as data inputs.

Although much terrain is above 3000 feet along the Cumberland Front, no stations are officially inputting any data into modeling now that the Black Mountain Cooperative has closed.

So initial lifting during NW Flow snowfall events continues to be under-estimated by both models and forecasters, with too much emphasis consistently placed upon what is the secondary lifting zone ( Blue Ridge ) in this type of flow.

Relationships between NW flow snowfall and topography in the Southern Appalachians, USA ( Baker Perry and Charles Konrad )

I applaud Baker Perry & Charles Konrad for highlighting this fact years ago, yet it seemed to make little difference in the general forecast community to again exemplify the hole of disconnect that exists between operational forecasters in private, commercial and government sectors with those in the field doing on the ground research.

Even this above graphic is MUCH under-estimated since it incorporates no data from the snowiest mountain mass in Virginia where model errors on snowfall of all trajectories, but certainly on the NW Flow snowfall events, are much more than 30.5 cm listed for the Wise NWS Cooperative.

Wise tends to receive 40-60% less snow than upper elevations in the High Knob Massif, which is obvious to anyone in this area who may live or visit the area.  Many residents live above 3000 feet on both the Wise & Scott County side of the high country.  Leaving the portion in Scott County consistly out of most winter advisories is another problem that needs addressing ( it could be solved easily by joining that portion of Scott County north of the Clinch River with Wise County in winter weather settings such as NW flow ).

Moisture extraction along the initial lifting zone of the Cumberland-Allegheny Front on NW Flow snowfall means there is less moisture in a vertical atmospheric column to be precipitated out along the secondary lifting zone of the Blue Ridge, such that air has to be lifted to higher elevations in order to achieve as much snowfall.  That is why it is nearly impossible, if not impossible, to find locations along the Blue Ridge where 75-100″+ of snowfall occurs annually at elevations as low as 3000 to 4200 feet ( *** ).

***Mount LeConte, at 6400 feet above mean sea level, at the summit level of the Great Smokies, on the windward side of the mountain range, has an annual snowfall average of around 100″ .

When Great Lake moisture transport into the initial lifting zone is vertically shallow in nature then it is impossible in many cases, regardless of elevation along the Blue Ridge, to achieve as much snowfall as on the Cumberland-Allegheny Front.  If moisture transport is deeper; however, and also if orographic forcing is moderate-strong + upper dynamics are also favorable, then snow amounts reported at higher elevations along the Blue Ridge can match or occasionally exceed those at lower elevations along the Cumberland-Allegheny Front.  This is especially true for peaks standing along the front of the Blue Ridge, such as Roan Mountain and Mount LeConte.

For forecast purposes, in particular, forecasters remain too limited and under-estimate the amount and coverage of NW flow snowfall along & west of the Cumberland Front as such events produce widespread accumulations ( # ).  While this is of course partly due to a continued need for better terrain resolution by forecast models, it is also due to a fact that despite decades of forecasting and recorded climatology there never seems to be the needed adjustments.

#The widespread snow having enhancements with superposition of snow squalls and snow streaks developing in the 925 to 850 MB flow field to add to the widespread coverage.  Leeward of initial lifting, coverage of accumulating snowfall is typically hit or miss and too often this hit-miss nature that is so common in downslope locations ( like the Great Valley ) is applied to the primary lifting zone in forecasts ( when only heavier local amounts should be stressed upon an otherwise widespread accumulation ).

The main focus from my perspective as both a researcher and teacher is this most important fact…the human brain remains the superior forecasting tool and is often forgotten with too much emphasis being placed upon computer model output, statistics, fancy graphics, and zone forecasts.  Each forecaster should ideally make their own personal forecast from scratch, using raw model data and past climatology of analogous events, and if it then agrees with other forecast sources then that is great.  In other words, do away with copy, slightly adjust, and paste!

Mountain Area Forecast ( Jan 22-25 )

An ALERT Continues For Strong-Gusty SSE-SW Winds During Monday Night Into Tuesday Morning As Temps Begin To Turn Colder.  The Coldest Air Is Expected To Arrive Tuesday Night Into Wednesday.

A general SSE-S wind flow and mild conditions will continue through Monday evening, with highest elevations and favored mountain wave zones having the strongest wind speeds.  Local gusts over 50 mph will be possible.

A wind shift to SW overnight is expected to begin to focus the strongest winds into the Wise & Sandy Ridge plateaus and upper elevations of the High Knob Massif during the predawn to mid-morning period Tuesday, with general strong-gusty conditions across the area in a widespread nature along and behind the passage of a cold front.  Air temperatures Tuesday will display falling trends during mid-late afternoon, following any small rises or steady nature through early Tuesday PM.

Cold air will surge into the mountains Tuesday night into Wednesday with enough low-level moisture to generate some snow showers, flurries, and a chance for local squalls.

Monday Night Into Tuesday Morning

Mostly cloudy and mild through the evening with a chance of rain showers.  Rain showers becoming likely overnight.  A chance of thunder.  Turning chilly by morning.  Windy.  SSE to S winds shifting SW at 10-20 mph, with higher gusts below 2700 feet.  Winds SSE to SW at 15-25 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures dropping into the low 30s to low 40s by morning ( coldest at highest elevations ).  Wind chills dropping into the 20s to low 30s, except 10s at the highest elevations, by morning.

Tuesday Morning Through The Afternoon

Predawn to mid-morning clearing giving way to cloudy skies.  Turning colder.  Gusty.  A chance of flurries by late.  SW to W winds 10-20 mph with higher gusts.  Temps near steady to falling into the 20s at upper elevations and into the 30s at lower-middle elevations along and north to west of the High Knob Massif-Tennessee Valley Divide.  A little milder in downslope locations of the Clinch, Powell, and Holston river valleys.  Wind chills in the 10s and 20s, coldest at highest elevations.

Snowfall Forecast – General dusting up to 1″ between Tuesday Night & Midnight Wednesday ( locally more possible at upper elevations of the High Knob Massif )

Tuesday Night Into Wednesday Morning

Snow showers & flurries developing late into overnight.  Light snow accumulations.  Cold.  W-WNW winds 5-15 mph, with higher gusts.  Temps varying from the middle-upper 10s to the middle-upper 20s ( coldest at upper elevations ).  Low cloud bases with rime formation becoming possible at highest elevations.  Wind chill factors dropping into the 10s to low 20s, except single digits to around 0 degrees in gusts on highest mountain ridges.

Wednesday Morning Through The Afternoon

Partly-mostly cloudy. A chance of snow showers, flurries.  Light accumulations possible.  Cold & blustery.  WNW winds 5 to 15 mph with higher gusts.  Temperatures varying from upper 10s to lower 20s at upper elevations to upper 20s to lower 30s at low-mid elevations along and north to west of the High Knob Massif-Tennessee Valley Divide.  Wind chills in 10s to low 20s, except colder on highest peaks.

Wednesday Night Into Thursday Morning

Partly-mostly cloudy.  A chance of flurries.  A heavier local snow shower possible during the evening.  WNW winds 5-15 mph, with higher gusts.  Temperatures widespread in the 20s and 10s ( coldest at upper elevations ).  Wind chills in the 10s and single digits ( below zero in gusts on highest peaks above 3500 feet ).

The potential for a significant storm system featuring a rain to snow transition is being monitored for the late weekend-early week period of January 28-29.  Stay tuned for updates.

Reference January 1985 Arctic Blast for a review of a great cold wave that froze the mountain landscape 33 years ago this week.

Weather Discussion ( Up-Down Pattern )

January 23 Update

This update is to include light snow accumulations with activity developing late Tuesday night into Wednesday, amid limited moisture, and to slightly adjust temps.

A little blush of color on clouds that increased during Tuesday afternoon to cap off a very windy period.

As expected, the strongest winds developed in the Wise area as low-level winds shifted SW overnight into Tuesday with gusts topping 40 mph.  A peak gust of 52 mph was recorded by the Black Mountain Mesonet, with no doubt higher gusts in open meadows from the High Knob peak to Camp Rock.

*The Camp Rock Meadow ( a quarter to one-half mile long ) is often very windy on air flows possessing both southern components and northerly components ( elevation around 3900 feet ).

Temperatures reached a mid-morning MIN then climbed amid sunshine to a early afternoon MAX before slowly beginning a decline during mid-late afternoon.

*The MAX temp for the day occurring just after Midnight.

Although moisture is limited with incoming continental Polar air, given Great Lake moisture injection is missing the southern Appalachians toward the north, a couple of upper air waves in the flow field will combine with WNW upslope to generate snow showers and flurries.  A heavier burst of snow, on at least a localized basis, can not be ruled out.

Most of the activity is expected overnight into Wednesday morning with the initial cold air advection and developing WNW upslope, then again late Wednesday with a stronger upper air wave and 850 MB thermal MIN.

*I expected the heaviest snow to fall in the area of Canaan Mountain and Canaan Valley in the northern mountains of West Virginia, with totals of more than 6″ being possible there into Thursday AM.

Previous Discussion

A up-down temperature regime is expected to rule the remainder of January 2018, with increasing signs that another prolonged wintry lock-down will develop during February across the eastern USA.  Could the worst of this 2017-18 winter season be upcoming?

Frequent mountain waves were observed through Monday as strong winds blew across the High Knob Massif ( below ).

Although most mid-upper elevations locations were in the 50s during Monday, temperatures varied from upper 40s at the summit level of the High Knob Massif to middle 60s in downslope locations like Clintwood ( 64 degree PM MAX ).

Strong low pressure over the center of the nation began to impact the mountains Monday, with gusty winds and a mild flow of southerly air ( it is difficult to get a truly warm feel to the air at the top of the high country in January, with 40s and wind gusts over 30 mph, but compared to last week it was a ”balmy” day with modified maritime tropical air mass advection ongoing in advance of a cold front ).

Showers, with embedded thunder, are developing in the warm sector of the current cyclonic storm where warm conveyor belt air is being lifted ahead of the system’s cold front and its descending dry conveyor belt air which is sinking downward from the mid-upper troposphere to generate a dry slot that is visible on satellite imagery.

Thunderstorms developing in the warm sector west of the mountains are forming in a Theta-E ridge, or low-level axis of available potential energy, which is forecast to fade as activity propagates east into the mountains, thus I have only a chance of thunder as the front approaches.

Observe the large swirl of the current cyclone dominates this view of North America, with a pronounced comma-head of low clouds in its cold conveyor belt that have risen beneath the warm conveyor belt into middle portions of the troposphere and wrapped cyclonically around the center of low pressure.

A pronounced dry slot and warm conveyor belt ( with a Pacific-Gulf of Mexico moisture tap carrying deeper moisture south and east of the Appalachians ) are also clearly visible.

Due to the large, cyclonic circulation around this system air will be turning cold on SW winds as it begins to pull a mass of air featuring continental Polar properties into the area during the predawn-morning hours of Tuesday.

Note that while this is different from the continental Arctic air mass of last week, a rather dramatic change will still occur with falling temperatures & wind chills Tuesday into Wednesday.

Enough low-level moisture will be present to generate snow showers, flurries, and the chance for some local squalls as cold air increases Tuesday Night-Wednesday.

With the best low-level moisture currently expected to flow into the central-northern highlands of West Virginia, that is where the greatest snowfall amounts will likely occur.

A WNW flow field will favor heaviest amounts along and west of the Cumberland-Allegheny Front, as well as within a narrow zone from Mount Rogers southwest along highest elevations of the Tennessee-North Carolina border.  Lifting will be aided by passage of a couple upper air waves, such that amounts of 1-2″ will be at least locally possible in the southern Appalachians ( stay tuned for updates ).

Increased wave forcing into the stratosphere, with warmth building above Siberia expected to move across the Pole to above Alaska and western Canada, will aid the rebuilding of tropospheric ridging upstream of the eastern USA during the next 1-2 weeks.

Looking down the rocky road, it appears that much more significant cold air will return to the eastern USA with a variety of factors beginning to come into alignment.

A changing SOI ( Southern Oscillation Index ) with an eastward propagating Madden-Julian Oscillation wave is forecast to enter cold phases for the eastern USA.

It is looking like some very interesting weather times are upcoming as this 2017-18 winter season is not even close to being finished ( with respect to cold and snow ).

Mountain Area Forecast ( Jan 20-22 )

Strong SSE-SSW Winds Will Be Developing By Late Monday Into Monday Night As The Next Weather System Arrives With Colder Air & Falling Temps Expected During Tuesday ( January 23 )

Former Alert

Remain Alert For Possible Black Ice From Refreezing

Strong & gusty winds will continue to generate notable wind chills along mountain ridges and plateaus through Saturday, with low cloud formation likely along and to southwest of the High Knob Massif and Tennessee Valley Divide enhancing chilly conditions ( general cloudiness across the remainder of the area with possible downslope breaks northeast of the high terrain ).

Overnight Into Saturday Morning

Increasing clouds overnight into morning.  Windy along mountain ridges & exposed plateaus.  SW winds 8-18 mph, with higher gusts, at elevations below 2700 feet.  Winds SW at 15-25 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures varying from 10s in colder valleys to the lower 30s, with valley temps tending to rise toward morning.  Wind chills in the 10s and 20s.

Saturday Morning Through The Afternoon

Mostly cloudy.  Chilly.  Downslope breaks in northern portions of Wise-Dickenson and Buchanan counties.  SW winds 10-20 mph with higher gusts below 2700 feet.  WSW-WNW winds 10-25 mph, with higher gusts, at elevations above 2700 feet.  Temperatures in the 30s to mid 40s.  Wind chill factors in the 20s & 30s ( coldest at upper elevations ).

Saturday Night Into Sunday Morning

Partly to mostly cloudy.  Winds SW-W at 5-15 mph, with higher gusts, mid-upper elevation mountain ridges and exposed plateaus.  Temperatures in the 20s in sheltered mountain valleys versus near steady or slowing rising in the 30s to low-mid 40s on mountain ridges. Wind chills in the 20s & 30s, coldest at the upper elevations.

Sunday Afternoon

Partly to mostly cloudy.  Winds S-WSW at 5-15 mph, with higher gusts.  Temperatures varying from the low-mid 40s to the low-middle 50s.  Wind chills in the 30s along upper elevation mountain ridges.

 Sunday Night Into Monday Morning

Partly to mostly cloudy.  SSE-S winds 5-15 mph on mountain ridges-plateaus below 3000 feet.  S-SW winds 5-15 mph with higher gusts at upper elevations.  Temperatures from 20s to low 30s in colder valleys to the 40s on mid-upper elevation mountain ridges-exposed plateaus.

Monday Afternoon

Mostly cloudy & windy.  SSE-S winds 10-20 mph, with higher gusts, below 2700 feet.  S-SSW winds 20-30 mph, with gusts 40-50+ mph, at elevations above 2700 feet.  Temps varying from 40s at highest elevations to the mid-upper 50s.

Weather Discussion ( Slow Warming )

Saturday Aftenoon Update

I updated for removal of drizzle chances this afternoon, leaving in a small chance for tonight with air not far from being saturated at high elevations.

Temperatures have mainly climbed into the 40 to 45 degree range, amid gusty S-SW winds.

The January 20 MODIS satellite image did capture cloud breaks across portions of Dickenson-Buchanan counties  and into adjacent counties.

Previous Discussion

Low sun angles ( 32 degree solar angle in Wise on Jan 19 ) and snow cover impacted air temperatures Friday and will continue to do the same through Saturday, with strong and gusty winds at mid-upper elevations adding to the chill.

Although much milder than the peak of recent bitter cold, air remained chilly on the Campus of UVA-Wise Friday with notable chill factors being created by gusty SW winds.

Several interesting features on the MODIS Terra image for January 19, with widespread snow cover remaining from the Piedmont of North Carolina and Virginia across the Appalachians into the Midwest, and a deck of low clouds creeping up the lower Mississippi Valley.

If low-level moisture over the lower Mississippi Valley is lifted up over the mountains into Saturday it will really keep the lid on air temperatures, with best odds of this happening being where the low-level SW flow rises beneath the 850 MB field.  Temperatures may struggle to get above freezing atop the high country during Saturday, such that any travel along Route 619, 238, 237, 704, to note a few, should be done with caution.

Friday afternoon MAXS varied from the low 30s atop the High Knob Massif to 43 degrees in Clintwood; although, most middle to upper elevation locales felt significantly colder with gusty SW winds.

SW winds are really cranking tonight at mid-upper elevations and are at a threshold where an alert should actually be issued, but I have them headlined at the top.

When factoring in the frequent gusts, conditions continue to feel like the 10s at high elevations and low-mid 20s in Wise.  Sheltered mountain valleys are just cold with calm conditions ( 17.6 degrees in Clintwood as of 12:50 AM Saturday ).

The Bottom Line…Gusty winds, low sun angles, and increasing low-level moisture over lingering snow cover will all be working against warming to keep conditions chillier than models indicate, with the most aggressive warming likely Sunday PM into Monday ahead of colder air returning by Monday Night into Tuesday.

If Winter 2017-18 is truly destined to become one of the great cold winters then settings like this will be rather common, with models generating head-fakes for those who bite and warm periods which end up being shorter than models forecast.

Although it appears that winter returns with a real vengeance into February, this can not yet be known for certain.  Seasonal snowfall continues to run well below average, so lovers of snow are hoping that the biggest falls of snow are yet to come ( as have often been observed during February-March and even April ).  Time will tell.

Mountain Area Forecast ( Jan 17-19 )

Remain Alert For Possible Black Ice As Well As Slick Stretches On Secondary Roads.  Bitter Conditions Will Continue Into Friday Morning.

Although coldest air temperatures will be felt in mountain valleys, with single digits to local below zero readings in coldest valleys at upper elevations into Friday morning, breezy to gusty winds will continue to produce notable wind chills along mountain ridges.

The development of strong inversional conditions overnight are expected to weaken with vertical mixing Friday, but surface air temperatures will continue to run cooler than forecast models indicate until widespread snow cover melts.

Melting and sublimation are endothermic processes that absorb heat from the environment, with cooling being a result.  Insolation, or incoming solar radiation, from the sun is partially applied to melting and sublimating the snow instead of heating up surfaces that then heat the overlying air.

In addition, of course, snow possesses a high albedo ( reflectivity ) such that up to 80-90% of insolation is reflected and not absorbed when snow is fresh and clean ( albedo tending to decrease as snow ages ).  Time and time again we observe forecast temperatures being too high when snow cover is on the ground.  In complex terrain, factors such as orographically forced downsloping can help offset this effect in part as was observed during the afternoon of January 18 when 31.6 degrees was the MAX temp observed in Clintwood.  I had predicted max temps up to low 30s anticipating that the downslope influence on SW flow would partially offset the cooling effect of widespread snow cover.  So Clintwood 1 W, at nearly the same elevation as Tri-City Airport ( TRI ) was 4 degrees warmer during the afternoon due to downsloping on SW winds versus TRI where a SW wind is an up-valley wind possessing a rising trajectory ( not sinking across mountains ).

Previous Alert

ALERT For Bitterly Cold Conditions And Slick Roads, Especially Secondary Mountain Roads, Into Thursday

Many roads will remain snow covered and slick into this morning, with secondary roads likely remaining hazardous through today into tonight-Thursday AM due to bitterly cold temperatures.

Additional flurries, snow showers and instability supported squalls will be possible into Wednesday evening.  New fluffy amounts of up to 0.5-1″ will be possible, with locally greater amounts within the High Knob Massif.

Wednesday Morning Through The Afternoon

Partly to mostly cloudy & bitterly cold.  Flurries, snow showers and local snow squalls remaining possible.  NW winds 5-15 mph with higher gusts.  Temperatures nearly steady in the single digits at upper elevations and 10s at lower to middle elevations along-north of the High Knob Massif-Tennessee Valley Divide.  Wind chill factors -5 to 10 degrees at lower-middle elevations below 2700 feet, and from -5 to -15 degrees in upper elevations.

Wednesday Night Into Thursday Morning

Partly to mostly cloudy.  A chance of flurries and light snow.  Riming at highest elevations.  NW-W winds 5-10 mph, with higher gusts, on mountain ridges and exposed plateaus below 2700 feet.  NW winds 5-15 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures varying from -15 to 5 degrees above, tending to rise on high mountain ridges overnight into morning.  Below zero mins likely in many valleys if skies clear.  Wind chills 5 above to -5 below zero at elevations under 2000 to 2500 feet, and -5 to -25 below zero over 2500 feet.

Thursday Afternoon

Partly to mostly sunny.  SSW-WSW winds 5-10 mph, with higher gusts, below 2700 feet.  WSW-WNW winds 10-20 mph, with higher gusts, on upper elevation mountain ridges.  Temperatures in the 20s to lower 30s.  Wind chill factors in the 10s to low 20s ( coldest highest elevations ).

Thursday Night Into Friday Morning

Mostly clear.  Large vertical temperature spread developing between frigid mountain valleys & milder mountain ridges & exposed plateaus.  Winds SSW-W at 5-15 mph with higher gusts, especially on upper elevation mountain ridges.  Light valley winds.  Temperatures varying from below 0 degrees in coldest mountain valleys to upper 10s & 20s on exposed middle to upper elevation mountain ridges.  Wind chills in the 10s to lower 20s, with single digits possible in gusts on highest peaks.

Friday Afternoon

Mostly sunny.  Seasonally chilly.  SSW-WSW winds 5 to 15 mph, with higher gusts.  Max temperatures rising into the upper 20s to lower 30s at upper elevations to the upper 30s to lower 40s ( warmest in downslope locations ).  Wind chill factors in the 10s and 20s to low 30s ( coldest at highest elevations in the High Knob Massif ).

Terrain models in combination with the European group are advecting low-level moisture into the area on gusty SW winds during the weekend, which would really put the lid on temps.  Please stay tuned for updates and do not plan to break out the ”bermuda shorts” just yet!  At least, not in the mountains.

Weather Discussion ( Bitter Air )

Recap & Analysis Of Event

A nice GOES-16 composite as the Circle of Illumination is poised to pass over the area as Earth rotates from daylight into darkness on January 18, 2018.

Northeast Canada and the northeastern USA are already going into night, with city lights noted around Lake Ontario.  Observe snow cover across the piedmont of Virginia & North Carolina, as well as from the mountains west and northwest toward the open waters of Lake Michigan.

The coldest daylight period of the 2017-18 winter season to date was observed Wednesday as continental arctic air was able to invade the region across extensive snow cover that stretched from the Appalachians into Canada.

Note that flat surfaces and gently rolling terrain will appear brighter than complex terrain with snow cover; therefore, it is not possible to tell depth with this type of visible image.  I always find it interesting that whenever Powell Valley has snow cover it will appear much brighter than the adjacent high country even though it always has much less snow depth.  Part of that is due to the open nature of the Valley versus the thickly forested massif, but mostly this difference is due to the changes in albedo, or reflectivity, that are associated with highly complex, forested terrain.

A parting of the clouds was timed right for the daily MODIS pass of NASA’s Terra Satellite to capture the snow covered expanse of the High Knob Landform ( lower right above ) surrounded by lingering clouds ( close up below ).

Day time maximums barely broke above 0 degrees atop the High Knob Massif where the morning low dipped to around -8 degrees below zero ( with much colder wind chills ).

Temperatures tonight ( Wednesday ) have again dropped below 0 F.

Morning snow depths generally varied from 4″ to 8″ across the high country, with 2″ to 4″ of new snow adding to old snow already on the ground.

Joe & Darlene Fields had 2.5″ of new snow in the High Chaparral community, on top of 2″ already on the ground ( a general 3″ to 4″ or 4″ MEAN depth at their southern exposed location ).

Note a single snow does not = a snowpack.  Multiple snows that generate snow cover add to form a snowpack.  The exception to this might be when a monster snow dump occurs such that it lingers for a long time and experiences a variety of changing weather conditions.  High country in the High Knob Massif is certainly one of the very few places in Virginia where true snowpacks tend to develop in winter.  The largest snowpack recently observed was during February 2015 when multiple snowstorms generated 3 to 4 feet of average depth.

The winter of 2009-10 featured a long-lived snowpack with a general 1-2+ feet of snow depth across the high country of the High Knob Massif from December into March.

Flurries and light snow has been falling atop the High Knob Massif since before sunset, and recently have started again in Wise and Clintwood.  As typical, Lonesome Pine Airport reported the “hottest” afternoon temp at its elevation.

The official NWS maximum reached 14.1 degrees in Clintwood at 1560 feet above mean sea level.  If the mean Environmental Lapse Rate of 6.5 C degrees per kilometer is then applied ( 3.5 degrees Fahrenheit per 1000 vertical feet of elevation increase ) the result would translate to a MAX temperature of 14.1 – 3.9 = 10.2 degrees for the elevation at Lonesome Pine Airport ( or just about what was recorded at the 2650 feet elevation of Nora 4 SSE on Long Ridge ).

So whatever is causing the Lonesome Pine Airport air temperature to run too warm for its elevation, whether it be exposure near the runway, the radiation shield, a thermistor calibration problem, or a combination of factors it has now been ongoing for years.  How do I know, because in years past I could almost always look at my temperature and subtract 4 degrees F to get what LNP reported.  Other ASOS sites have reportedly also developed this problem!

The above being applicable to typical daytime conditions, as large temp differences typically develop at night between the exposed plateau and mountain valleys, or local sinks on the plateau, where cold air drains. 

A couple of factors made this a difficult system to forecast over the mountains.  Number 1, as I recognized, orographic forcing was to be weak.  This was good if you were a lover of snow in downslope locations since it translated to a much lower magnitude of inverse forcing ( sinking air ).  It also generated less low-level lift on the upslope side.

I heard the WCYB crew drove the new StormTracker from the TRI along U.S. 23 to Norton, then along Alt. 58 back toward the Great Valley.  While I do not know exactly what they found, orographics would suggest that worst conditions would have been found from upper portions of Powell Valley, where U.S. 23 begins approaching the Overlook, on through Norton to Coeburn then improving upon dropping downward toward the Clinch River in St. Paul.  While elevation changes upon passing through the Cumbeland Front a couple of times would be a factor, the biggest impact typically would be that the above noted trek was on the windward or upslope side of the High Knob Massif.  In this case; however, orographics were weak so perhaps it did not make such a difference like often observed with stronger forcing.

With NW-N flow the Jasper to East Stone Gap valley corridor is hindered by sinking air off Wallen Ridge and the Little Stone Mountain arm of the massif, with the significant lift typically being seen upon looking toward the great cliffs which line the flanks of the massif core ( right side of view when driving north along U.S. 23 from Duffield to Norton ).  The cliff line is a huge weather change marker, with locations above it often being obscured by clouds or snow-rime during winter events.

Number 2, as these graphics highlight, was harder to resolve since the system was undergoing a transition in its dynamics from being supported by upper air divergence- ageostrophically driven Direct Transverse Circulation into the RRQuad ( right-rear entrance region ) of a high altitude jet streak at 250-300 MB ( above ), to a setting driven by an Indirect Transverse Circulation in the LFQuad ( left-front exit region ) of a high altitude jet streak ( below ).  This feature proving most significant since its ageostrophic circulation was able to tap into Atlantic moisture!

Much of the weather we experience, as Lackmann notes, is the result of these ageostrophically driven secondary circulations which are formed by the atmosphere in order to re-establish thermal wind balance ( Gary Lackmann: Midlatitude Synoptic Meteorology ).  That is a very nice and important way to view instantaneous states of the fluid atmosphere ( weather ).

 The isentropic lift which I outlined in the 011418 Forecast  generated widespread snow, so a hit or miss of the forecast was not in question, just the amounts and where would any enhanced bands develop.  Enhanced snowbands developed both west of the mountains and east of the mountains, but due to the transitioning phase were generally lacking over the high terrain of the Appalachians.

Had orographic forcing been stronger it could have helped to make up for a lack of upper air dynamics, with the lift generated by the High Knob Massif still doing well given its highly exposed nature as evidenced by the miles and miles of rime coated terrain alone.

The transitioning in the upper dynamics, as noted above, placed the main mountain chain of the Appalachians in its weakening phase.  Ideally, of course, as past climatology well records, the greatest systems to impact the mountains occur with phasing of strong orographics with strong upper dynamics.

The closest enhanced band fell along the Daniel Boone National Forest in eastern Kentucky, with significantly higher amounts in local places in far western Kentucky.

Totals of 4″ on Beech Mountain and 6″ on Mount Mitchell were among the highest reported in the NC mountains, with Mitchell closest to the developing left front exit region.

Mount LeConte, at the top of the Great Smokies on the western side of the Appalachians, reported only 1″ of snowfall and depth.

Another notable aspect, of course, being much milder temps along the Blue Ridge and farther south across high peaks in the Smokies versus locations amid bitter surface-850 MB air along and west of the Cumberland-Allegheny Front ( which has been a trend during most of this 2017-18 winter ).

Just prior to sunset, and thickening clouds, the webcam was able to capture a line of Kelvin-Helmholtz waves with other orographic wave clouds.  Note they appear like ocean waves and are always great to observe.

Previous Discussion

Flurries and light snow continues to fall from Clintwood to the summit of High Knob as of 4:30 AM Tuesday; although, this is generally not being picked up by Doppler.

A total of 2.6″ of new snow was measured in Clintwood at 3:00 AM, as steady, fluffy flakes continued to fall ( around 20:1 density and getting lower as the temperature continues to drop ).

Air temperatures have dropped below zero at the top of the mountains, even with low clouds and light snow continuing.  Riming on the anemometer is likely causing wind speeds to be reported too low ( as orographic cloud vapor can be seen blowing across the summit of Eagle Knob, where riming is ongoing ).

A dramatic temperature drop was observed during Tuesday afternoon and evening as arctic air surged into the western slopes of the mountains.

Up to 30 degrees of temperature difference was observed between upper elevations in the High Knob Massif and the Tri-Cities ( lower 40s ) prior to cold air spilling across the mountains into the Great Valley of northeastern Tennessee and southwest Virginia.

This was part of a huge contrast in weather conditions across the Appalachians during Tuesday afternoon.

Mount Mitchell missed out on the January 12-14 snow event and had no snow prior to Tuesday night into Wednesday ( when snow should have finally covered the highest mountain in the East ).

A vigorous upper air wave will cross the mountains through Wednesday afternoon, with a pocket of very cold air aloft, so despite limited moisture in the vertical column this will continue to offer the chance for snow showers, flurries, and even some local squalls…especially on the upslope side of the mountains with respect to NW-N air flow.

Regardless of additional snowfall a bitter Wednesday is upcoming, even with some arctic sunshine this afternoon.

Mountain Area Forecast ( Jan 14-17 )

ALERT For Accumulating Snowfall From Mid-day Tuesday Into Predawn Hours Of Thursday, With Bitterly Cold Air Developing Tuesday Night Into Wednesday

A storm system with two phases, defined by the processes or mechanisms by which snow will be generated, will impact the mountain area from Tuesday afternoon into Wednesday night.

Phase 1 develops Tuesday with widespread snowfall generated by isentropic lifting and an influx of some moisture from the Gulf of Mexico.  General 1″ to 3″ amounts are expected to accumulate by sunset Tuesday.  Due to interaction between the two processes I am highlighting, I now have posted an alert for heavy snowfall late Tuesday afternoon into Tuesday evening.

A Heavy Snow Alert For Late Tuesday Afternoon And Tuesday Evening For Locations Along & Adjacent To The Cumberland Mountains

My latest analysis suggests that the arctic cold front will bring these two Phases together late Tuesday into Tuesday Night so I have now put out an Alert for Heavy Snow as the arctic front and upslope flow interact with deeper moisture for a period of time. I now think heavy snow will become widespread along the upslope side of the mountains, especially, with squalls remaining possible into Wednesday ( as already indicated ).

Phase 2 now develops by Tuesday sunset and continues through Wednesday evening ( possibly predawn of Thursday as flurries ), with the focus shifting to NW upslope snow, squalls & flurries.

A general 2″ to 3″ of snow is now expected from sunset Tuesday into Wednesday, especially within the favored upslope belt along and northwest of the Cumberland-Allegheny Front and possibly in a more narrow zone from Mount Rogers-Whitetop southwest along the Tennessee-North Carolina stateline.

Due to increased low-level lapse rates, local accumulations may also occur into the Great Valley on Wednesday.

Snowfall Forecast
Tuesday AM – Thursday AM
( January 16-18 )

Phase I
( 10 AM to 5 PM Tuesday )

A widespread 1″ to 3″

Phase II
( 5 PM Tuesday to 7 AM Thursday )

2″ to 3″ along and west-northwest of the Cumberland Front and in narrow zones near Clinch Mountain and from Mount Rogers to the summit level of the Smokies

Locally up to 1″ within downslope locations of the Clinch, Powell, Holston-Great Valley corridor in NE Tennessee and SW Virginia

Storm Total Snowfall ( 7 AM Tuesday-7 AM Thursday )

3″ to 6″ with locally higher amounts possible in the High Knob Massif

Locations along and west to northwest of the Cumberland-Allegheny Front will be most favored for the higher snow totals during the entire event ( Phases I + II )

*Reference my updated forecast discussion for more details.

Sunday Night Into Monday Morning

Partly-mostly cloudy.  A chance of morning flurries.  Light valley winds.  Winds becoming SSE-SSW at 5-10 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet.  SSW-WSW winds 5-15 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures in the single digits & 10s, coldest in the upper elevations and mountain valleys with snow cover at low to mid elevations.   A tendency for steady to slowly rising temps on mid-upper elevation ridges overnight.  Wind chills in single digits & 10s on exposed mountain ridges, except below zero along highest ridges by late evening-overnight.

Monday Afternoon

Partly to mostly cloudy ( mid-high clouds ).  SSW-SW winds 5-15 mph, with higher gusts, below 2700 feet.  SW winds 10-20 mph, with higher gusts, above 2700 feet.  Temperatures varying from the mid 20s to the mid-upper 30s.  Wind chills in the 20s on middle elevation ridges & plateaus and in the 10s at upper elevations ( single digits in gusts high peaks ).

Monday Night Into Tuesday Morning

Mostly cloudy.  SSW-SW winds 5-15 mph with some higher gusts on mountain ridges-plateaus below 2700 feet.  SW winds 10-20 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures varying from the lower 20s to around 30 degrees.  Wind chills in the 10s to lower 20s, with single digits in gusts at highest elevations.

Tuesday Afternoon

Snow developing.  Heavy at times.  SW winds shifting NW-NNW at 5 to 10 mph, with some higher gusts.  Temperatures near steady to falling in the 20s during mid-late afternoon, falling into 10s at upper elevations toward sunset. Riming at upper elevations.

Tuesday Night Into Wednesday Morning

Snow giving way to snow showers & snow squalls.  Whiteout snow bursts possible, especially along and northwest of the Cumberland Front ( High Knob Massif and Tennessee Valley Divide ).  Turning bitterly cold.  NW-N winds 5-10 mph with higher gusts.  Temperatures dropping into the single digits above and below zero.  Wind chills 5 above to 10 below zero, except as cold as -20 below zero or lower on highest peaks. Rime formation at upper elevations.

Wednesday Morning Through The Afternoon

Mostly cloudy & bitterly cold.  Flurries, snow showers and snow squalls ( bursts of snow ).  NW winds 5-15 mph with higher gusts.  Temperatures nearly steady in the single digits at upper elevations and the 10s at lower to middle elevations along and north of the High Knob Massif and Tennessee Valley Divide.  Wind chill factors 0 to 10 degrees at lower-middle elevations, and 0 to -10+ degrees below zero at upper elevations.  Blowing & drifting at high elevations in the High Knob high country.

Weather Discussion ( Another Blast )

An array of beautiful lenticular ( mountain wave ) clouds at sunset signals that some interesting weather is on the way.

As I have been highlighting now for days, a system with two distinct phases will impact the mountain region during the next couple of days.

Phase 1, as I highlight above using the 850 MB moisture field, is essentially associated with the warm conveyor belt. Streamlines show some connection to the Gulf of Mexico to denote that higher energy air, with latent heat, will advect northward and will be rising and undergoing condensation.

The UCAR-COMET Project

Although Phase 1 will not have a huge connection to the Gulf of Mexico, there is still a notable warm conveyor belt that is showing up on the modeling ( as noted previously ) and to be a warm conveyor belt it does not need to have a textbook type of Gulf connection ( indigenous to the USA ).

This process can be envisioned by looking at the Monday 294K surface at 7 AM, with air at the 800 MB level near the Gulf of Mexico that will begin to turn northeast toward 700- 600-500 MB air ( air will begin blowing across isobars from higher to lower pressure = rising air along the isentropic surface ).  The process noted at 7 AM ( above ) is now being observed on the 7 PM Monday chart ( below ), with moisture transport denoted by mixing ratio contours in green.

Due to diabatic processes, like latent heat that is released during condensation and freezing, the continuity of the isentropic surface will tend to be disrupted and the level to see processes best may need to be changed or looked at in vertical cross-sections.

For more information reference: Isentropic Analysis from which much of this information is courtesy of the late Dr. James ( Jim ) Moore who helped me learn about this important way to analyze the atmosphere.

Most everyone seems to agree on Phase 1, with widespread Winter Weather Advisories now in effect to 7 PM ( Wise ) or Midnight ( Dickenson-Buchanan counties ) on Tuesday.  The second phase of this system should not be neglected and is likely to generate Winter Storm Warning criteria as it will add to initial isentropic lift snow ( warning criteria was also reached in the High Knob high country during the previous January 12-14  weather event ).

Air begins turning bitterly cold Tuesday evening with NW-NNW upslope flow and a low-level moisture connection to the Great Lakes, such that snow showers and squalls will be developing in the upslope flow behind the widespread snow associated with Phase 1 that will be moving eastward.

Although atmospheric moisture in a vertical column will be dropping to between 0.10″ to 0.20″, air temps will be in the single digits above and below zero ( at top of mountains ) by Wednesday morning.

Cyclonic vorticity advection + a pocket of -30C air aloft will be moving over the mountains from Wednesday morning into the afternoon ( above ).  This will help increase low-level lapse rates to take advantage of what moisture is present amid the bitterly cold air ( below ).

As observed during the January 12-14 AM period, flakes of snow will be likely to fall along the upslope side of the mountains until the last low-level cloud dissipates!

The Bottom Line…Widespread snow develops Tuesday to impact the mountain region during Phase 1.  Expect hazardous travel as snowfall rates increase and temps begin dropping through the afternoon, with the heavy snow potential currently appearing to be increasing for late Tuesday afternoon into Tuesday evening.

The event does not end at 7 PM when current Winter Weather Advisories are set to expire, but instead will continue Tuesday Night into Wednesday with flurries, snow showers, and squalls ( some featuring whiteout bursts of snow in local places ).

While NW-N upslope flow will tend to favor the typical lifting zones, dynamics in the upper air and increasing low-level lapse rates means activity may not be restricted completely to the NW upslope flow corridors on Wednesday.  Bitterly cold temperatures and wind chills will make conditions worse, especially at middle-upper elevations.  Please take care.

Previous Discussion

A couple of Sunday morning views from the high country of the High Knob Massif where low temperatures dropped well below zero.  There is more of that coming!

Storm Total Snowfall
January 12-14

Joe & Darlene Fields
High Chaparral Community
4.5″

Steve & Cody Blankenbecler
Eagle Knob of High Knob Massif
*6.0″

*( 3-8″+ ground depths )

Morning view looking across lofty High Knob Lake Basin toward an inversion layer along the Tennessee Valley.

Snowflakes literally fell until the very last low-level cloud dissipated, with light snow-flurries all night into Sunday morning from Clintwood to Norton-Wise and into the high country of the High Knob Massif.

While the High Knob Massif may not be the tallest mountain in the Appalachians, it is one of the most distinct from high resolution satellites in space.  See if you can pick it out?

An aspect which helps make it such a prolific snow mountain in winter, precipitation enhancer + microclimate generator through all seasons is that its sprawling ( wide ) mass rises isolated within the atmosphere ( as clearly seen above from 22,300 miles up! ).

An array of mid-high clouds decorated the sky as Sunday afternoon temperatures held in the 10s to lower 20s within locations along and north of the High Knob Massif and the Tennessee Valley Divide ( forecasters observe the chilling, albedo effect, of snow cover ).

As most people who live in Wise know, the Airport tends to report the “warmer” air temperatures on the Wise Plateau, with Nora 4 SSE along the adjacent Sandy Ridge Plateau often being more in line with UVA-Wise and what many shaded thermometers read in Wise.

Sunday MAX temperatures varied from 22.1 degrees in Clintwood ( official NWS temp ) to low teens at the summit level of the High Knob Massif.

**The mean snow depth reached 2″ in Clintwood with a total snowfall of 3.2″ ( mostly a low density snow after the initial transition occurred in milder temps ).  Interestingly to some, perhaps, 1.7″ fell after 9 AM Saturday into Sunday morning.

The upcoming system should not be taken for granted given its nice upper air dynamics, with the only aspect holding me back from calling for a major dump of snow being that the orographic forcing will be weak-moderate.

Starting at the top, synoptic-scale lift into the right-rear quadrant of a 100-130+ knot jetstreak at 300 MB will be in a climatologically favored position to support widespread snow as the system develops Tuesday.

Air turns bitterly cold Tuesday night into Wednesday AM such that the bottom drops out of snow densities on NW-N upslope flow into the Appalachians.  Synoptic lift will also continue to be a factor aloft as divergence and cyclonic vorticity advection occurs into Wednesday morning.

While model QPF can be used as general guidance, one can not forecast a system like this using 10:1 density, especially as air turns bitterly cold into the NW upslope zones.  As just seen, snowfall with the most recent system was higher than model projections and lasted much longer than they said.

The Bottom Line…This system will impact a wide region due to general isentropic lift of higher energy air above lower energy air as part of Phase 1 during the day Tuesday.  If the shift to NW upslope is faster and a little stronger it will enhance amounts along and west of the Cumberland Front versus the Great Valley; however, this type of setting can be favorable for the TRI area if up-valley flow occurs and/or the sinking on NW flow is weak given that the upglide process develops snow independently of the terrain  on a larger-scale.

Dr. Charles Doswell would say, upper level air is always over-running lower level air so we do NOT want to call it overrunning unless a physical mechanism is stated to explain what makes this over-running any different from other cases ( in my own words to highlight why I include a physical mechanism above ).  In this case a Direct Transverse Circulation will develop as “milder” air rises upward into the right-rear entrance of the upper-level jet and colder air sinks with development of an ageostrophic flow to covert potential energy into kinetic energy of the system.

Phase 2 develops Tuesday Night into Wednesday as advection ( transport ) of bitterly cold air begins with a focus shifting to NW upslope snow.  Although the low-level orographic forcing will tend to be weaker than this most recent system, upper air dynamics + weak-moderate forcing will combine with a plunge in snow density to support bursts of snow as nearly all moisture within the vertical column is forced out.

Stay tuned for later updates. 

Mountain Area Forecast ( Jan 11-13 )

Alert For Significant Frozen Precipitation And The Development Of Extremely Bad Road Conditions By Friday Evening With A Sharp Temperature Plunge Expected Initially Along And North To West Of The High Knob Massif & Tennessee Valley Divide During The 6:00 PM To Midnight Period Friday ( Including Far Western Lee County ) – Followed By Continued Drops And Very Low Wind Chills Into Saturday Morning

A wind shift to a northerly upslope direction, with influx of cold air, is currently timed for late Friday into Friday evening.  Due to initially shallow cold air advection a transition from rainfall to freezing rain will become possible first at mid-upper elevations within the lifting zone along and north of the High Knob Massif and Tennessee Valley Divide and Pine Mountain.  As the cold air deepens vertically a transition into sleet and snow will occur across the area.  Bitterly cold air and dangerous wind chills are expected to develop as temperatures drop into the single digits and teens at mid-upper elevations into Saturday morning.

Bitterly cold conditions will continue through Saturday with daytime temperatures expected to hold in the 10s to around 20 degrees at lower-middle elevations, and in the single digits to around 10 degrees at upper elevations, in locations along and north of the High Knob Massif & Tennessee Valley Divide.

ALERT For Ponding Of Water Along Roads And Strong Rises On Creeks With Upslope Rains Within The High Knob Massif-Black Mountain Corridor Into Friday In Advance Of The Temperature Plunge

As of 1:00 AM Friday more than 2.00″ of rain had fallen within upslope locations of the High Knob Massif and Black Mountain corridor of far southwestern Virginia.  Due to partially frozen ground, especially across northern slopes, run-off on creeks will need to be closely monitored in watersheds of the Cumberland, Clinch, and Powell basins.

Lingering ice along some creeks could also be problematic.  Folks living and driving along streams should remain on alert as periods of heavy rain continue to fall through Friday afternoon.

**A break in rainfall will be possible Friday morning before new rains, heavy at times, redevelop in advance of a strong cold front during Friday afternoon.  Remain alert for strong rises on streams.

Overnight Into Thursday Morning

Mostly cloudy ( mid to high clouds ).  Large vertical temp spread between sheltered valleys & gusty mountain ridges and exposed plateaus.  SE-S winds 5-15 mph, with higher gusts, along mountain ridges and plateaus below 2700 feet.  SSE-S winds 15-30 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures varying from around 30 degrees in colder, sheltered valleys to the mid 40s to low 50s on windy mountain ridges.  Rising valley temperatures overnight into morning in most locations.

Mid-Morning Thursday Through The Afternoon

Mostly cloudy with rain & showers developing into the afternoon.  Windy.  SE-S winds 10-30 mph, with higher gusts.  Temperatures varying from the lower 50s to lower 60s ( coolest at highest elevations ).

Thursday Night Into Friday Morning

 Rain likely with a chance of thunder.  Downpours possible, especially in upslope locations within the High Knob Massif-Black Mountain corridor.  SSE-S winds 5-15 mph with higher gusts along mountain ridges-plateaus below 2700 feet.  SSE to SSW winds 15-25 mph, with higher gusts, along mountain ridges above 2700 feet.  Low cloud bases with widespread dense fog at upper elevations.  Areas of fog at middle to lower elevations.

Friday Afternoon

Periods of rain.  Chance of thunder.  Downpours likely.  Winds shifting SW to NW at 10-20 mph, with higher gusts.  Sharply dropping temperatures toward sunset into early evening.  Temps in the upper 40s ( highest elevations ) to upper 50s prior to falling into the 30s shortly after sunset.  Widespread fog at upper elevations with orographic clouds, then dropping cloud bases into middle elevations behind the frontal passage; otherwise, local areas of fog.

Friday Night Into Saturday Morning

Rain changing to freezing rain, sleet, and snow.  Snow heavy at times after midnight.  Turning bitterly cold.  Winds NW-N 10-25 mph, with higher gusts.  Temperatures plunging into the 10s to around 20 degrees by morning, with single digits to 10 degrees at highest elevations, along and north of the High Knob Massif-Tennessee Valley Divide.  Milder amid downslope areas of the Clinch, Powell, Holston valleys ( 20s to around 30 degrees ).  Wind chills falling through the 20s into the 10s and single digits, except to below zero at upper elevations.  Riming upper elevations.

Saturday Morning Through The Afternoon

Mostly cloudy.  Bitter.  Snow showers & flurries.  NW-N winds 10-20 mph, with higher gusts.  Temperatures near steady in the 10s to around 20 degrees across lower-middle elevations, along-north of the High Knob Massif-Tennessee Valley Divide, and in the single digits to around 10 degrees across upper elevations.  Riming at upper elevations. Wind chills in the single digits above and below zero, except -10 degrees below zero or colder at highest elevations.

A prolonged period of winter cold, with additional snowfall chances, is being monitored through next week ( Jan 14-20 ).

Weather Discussion ( Huge Change )

Thursday Evening Update

My previous forecast holds with this update, with new additions being to highlight persistent rains that have dropped locally more than 1.50″ in the past few hours within portions of Wise & Harlan counties.

*More than 2.00″ of rainfall as of 1:00 AM Friday.

The latest run of the NAM terrain model has done a nice job of picking up this band, being forced by a combination of low-level lift and upper-level vertical motion into the right entrance region of a high altitude jet streak, as well as the enhancement with rise along the Blue Ridge in the extreme southern portion of Virginia and western North Carolina.

When a model initializes current conditions well then this helps to improve the odds that its short-term outlook will be on target, thus the thinking does not change that very bad conditions will become likely Friday evening into the morning hours of Saturday as a major temperature drop occurs with influx of bitter air into locations along and westward of the Cumberland-Allegheny Front.

Temperatures will begin to initially plunge first in the far western portion of Lee County, and along the Cumberland Plateau in Tennessee, as winds have more of a westerly flow component during Friday afternoon.

During Friday evening, as winds develop more of a NW-N flow component, the strongest temperature drops are then expected to become concentrated along and north to west of the High Knob Massif-Tennessee Valley Divide with a period of low-level terrain blocking likely acting to increase temp differences between Norton-Wise and the Tri-Cities more than the high resolution NAM 3 KM Model is suggesting.

Temperature drops will locally be stronger Friday evening in communities such as Norton-Wise, Clintwood and Pound than in Big Stone Gap, Gate City, Fort Blackmore and Dungannon as the flow works to accentuate terrain influences.

The Bottom Line…Conditions Are Expected To Become Bad Friday Evening Into Saturday Morning As A Major Temperature Plunge Interacts With Moisture.  Places Along And West Of The Cumberland-Allegheny Front Are Likely To Experience The Worst Conditions.

Towering cliffs along the Cumberland Front, the White Rocks of present day Cumberland Gap National Historical Park, were first described by early frontiersmen such as Daniel Boone.  The bulge of high country along this front associated with the High Knob Massif was a refuge for Robert ( Bob ) Benge, who terrorized the frontier of eastern Tennessee and southwestern Virginia during the long and bloody period of 1774-1794.

Bob Benge was a  Chickamauga Cherokee war chief, the mixed-blood son of a Cherokee woman and a Scots-Irish trader named John Benge ( reference Wikipedia ), with places such as Benges Basin and the Chief Benge Scout Trail in the High Knob Massif named after him today. 

Hazardous Roads Could Develop Across The Region Due To Such A Sharp Temperature Drop, Even In Locales Which Receive Little Frozen Precipitation.

Previous Discussion

A huge weather change back into winter is approaching the mountains as unseasonably mild conditions into Friday give way to a sharp temperature plunge Friday Night into early Saturday.  Precipitation types during the Friday and Friday Night period could run the gamut from wind driven rain, spiced with thunder, to freezing rain, sleet, and snow.

Temperatures currently are forecast to drop below freezing beneath the 850 MB level between 7:00 PM and 10:00 PM Friday evening, as an above freezing zone lingers aloft.  This vertical temperature profile would result in freezing rain and sleet.

All eyes in the forecast community should be on soundings, with the next few model runs being critical as to helping better determine how this period will unfold.

The positions of developing surface and 850 MB low pressure centers will be important, with a somewhat farther east solution than currently shown by the NAM Model allowing cold air to advect into the western front range of the Appalachians a little quicker.  A farther west solution would tend to delay the cold air.  Climatology in this type of digging upper trough setting suggests that a leeward low track ( east of the Eastern Continent Divide ) tends to be favored.

While the current NAM Model is in basic alignment with the latest European Model and its mean Ensembles & Control in showing a pronounced orographic signature, with heaviest snowfall along and upstream of the western front range of the Cumberland-Allegheny Front, there will likely be some changes in the placement of this during the next 24-48 hours.  Stay tuned for important updates.

Bitterly cold air flooding into the mountains will be a most notable part of this event.

Although changes may occur in this forecast, the drop in 850 MB temperatures on this type of air flow agrees with past climatology of observed events.

The development of the coldest 850 MB temperatures in the time between 7:00 PM Friday ( above ) and 1:00 AM Saturday ( below ) aligns with the strongest low-level orographically forced lifting along and north of the High Knob Massif and Tennessee Valley Divide on northerly air flow.  So while the complete three-dimensional nature of this complex terrain tends to not be fully resolved, one has to think that this run of the model is picking up on part of the orographics.  This aspect, along with general alignment with the ECMWF, is the main reason I chose this model to highlight how the Friday evening period will unfold ( remembering this is a setting that may, and will likely, change in some ways ).

I had highlighted this system for a long time as one to watch, and as it gets closer the reasons are becoming more and more distinct with a huge temperature gradient acting to drive imbalances within the thermal energy, mass and momentum of the atmosphere.  Quasi-geostrophic theory says that the atmosphere will thus respond by changing the vorticity structure of its mass field ( see map below ) and by changing the temperature of air parcels by adiabatic rising and sinking motions as demanded by thermal wind balance.

By 10 PM Friday Night the 500 MB trough ( above ) has taken on a negative tilt, with cyclonic vorticity advection as well as mass divergence ( not shown ) contributing to upward motion aloft as orographics lift the lower atmosphere.

A 30 to 40 degree temperature plunge is expected to occur between 4:00 PM Friday and 1:00 AM Saturday, with more declines through sunrise on Saturday.

These are surface temperature forecasts and do not reflect colder conditions at higher elevations nor the wind chills that will really make this a notable event.

This will mark the beginning of another prolonged period of cold conditions, and if significant snow accumulates it may be able to generate readings significantly lower than are being currently predicted into next week.

Meanwhile, lets not forget about the strong winds blowing across the high country which will tend to mix downward more into middle-lower elevations during Thursday.

Mountain Area Forecast ( Jan 9-11 )

ALERT For Areas Of Dense Fog Overnight Into Tuesday Along With Localized Icy Patches On Some Roadways

Lingering low-level moisture trapped beneath an inversion will continue to produce abundant fog overnight into Tuesday, with areas of drizzle.  While most temperatures will remain near to above freezing, a few valleys may remain near to below 32 F.

Radiational cooling by Tuesday Night into Wednesday AM will keep near saturated to saturated conditions at lower to middle elevations while drier air overspreads upper elevations, above 3000 feet.

An Alert For Mountain Wave Wind Gusts, And Strong General Winds At Upper Elevations, May Be Needed By Late Wednesday Into Thursday

Overnight Into Tuesday Morning

Low clouds with areas of dense fog.  SW-W winds 5-15 mph with higher gusts on mid-upper elevation mountain ridges and plateaus.  Temperatures widespread in the 30s.  Wind chills in the 20s to lower 30s ( coolest highest elevations ).

Tuesday Afternoon

Low clouds with areas of dense fog, especially at higher elevations.  Light winds, except W-SSW at 5-10 mph along upper elevation mountain ridges.  Chilly and damp with temperatures mainly in the lower-middle 40s.

Tuesday Night Into Wednesday Morning

Low clouds with areas of dense fog at lower-middle elevations.  Becoming partly-mostly cloudy at upper elevations.  Winds SSE-SSW 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges.  Temps in the 30s, except near steady or rising in the 40s along higher mountain ridges.

Wednesday Morning Through The Afternoon

Becoming partly-mostly sunny.  Milder and gusty.  SSE-S winds increasing to 10-20 mph with higher gusts.  Temps varying from 40s to low 50s in upper elevations to the upper 50s to around 60 degrees.

Wednesday Night Into Thursday Morning

Partly-mostly cloudy.  Windy.  Unseasonably mild.  SE-SSE winds 10-25 mph, with higher gusts, at elevations below 2700 feet.  SE-SSE winds 20-30 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures widespread in the 40s to around 50 degrees.

The potential for major storm development, with rain to snow and an influx of bitterly cold air, is being monitored for the late week and weekend period ( January 12-14 ).

Weather Discussion ( Brief Thaw )

Abundant low-level moisture is trapped beneath an inversion layer left over in wake of the Monday system which dropped everything but the kitchen sink on the mountain landscape ( snow, sleet, freezing rain, rain ).

If this low-level inversion does not mix out Tuesday, abundant moisture will continue as some terrain models suggest with drier air advecting into upper elevations by Tuesday Night into early Wednesday to set the stage for a very nice but increasingly gusty Wednesday.

Wednesday is looking to be the best day of the week, in general, as strong winds develop by Wednesday night into Thursday on SE-S flow to increase moisture into the Blue Ridge.

All eyes will then focus upon a upper wave digging into the eastern USA by later this week, with potential for phasing between sub-tropical and polar jet streaks suggesting the potential of major cyclogenesis ( storm development ).

Although details remain to be worked out, a setting like this could generate rain-thunderstorms in its warm sector and a synotpic-scale snowband with wrap-around and/or NW Flow snow developing on its cold side.  Stay tuned.

Mountain Area Forecast ( Jan 6-8 )

*Alert For Slick Conditions Today ( January 8 )*

While frozen precipitation types will be possible in all locations, a main concern today is frozen surfaces from more than a week of sub-freezing temps.  Even if air temperatures are above freezing surfaces subjected to prolonged bitter cold will not have had time to warm prior to the development of precipitation.

There will be an enhanced potential for frozen precipitation forms, including snow, within the SW flow upslope zone within the High Knob Landform corridor where SW air flow rises, such that temperatures will remain colder than forecast models predict from the Tennessee Valley Divide ( Norton-Wise-Sandy Ridge ) into portions of Lee County.  If snow develops within this zone then a general 1-3″+ will be possible; otherwise, other frozen types are expected from mid-morning into the afternoon.

Strong SW Winds Will Develop Sunday Night Into Monday At Middle-Upper Elevations Along The Cumberland Mountains

Although temperatures are expected to display near steady to rising trends across middle-upper elevation mountain ridges and exposed plateaus during Sunday Night into Monday, development of strong to ROARING SSW-WSW winds will continue to generate low wind chill values.  Wind gusts of 25-50+ mph will become likely as a low-level jet interacts with higher elevations.

Bitter Cold Temperatures Will Continue Into Sunday Morning As A Large Temperature Spread Develops In The Vertical Between Frigid Valleys & Milder Ridges

A rapid Saturday evening-night temperature drop is expected in mountain valleys as ideal cooling conditions develop.  Meanwhile, higher mountain ridges will begin to experience a slowing of falls and even rising temperatures overnight into Sunday morning as winds shift S-SW.  This will generate a large vertical temperature spread between colder valleys that drop below 0 degrees and milder ridges which rise upward through the 10s.

Saturday Night Into Sunday Morning

Mostly clear.  Bitter.  Large vertical temperature difference developing between frigid valleys and ”milder” mountain ridges.  Light winds becoming S-SW along high mountain ridges overnight-into morning at 5-10 mph.  Temperatures varying from below zero in colder mountain valleys and on highest peaks ( early ) to the single digits, then rising thru the single digits into the 10s along higher mountain ridges overnight into morning.  Wind chills from 5 above zero to -15 degrees below zero on mountain ridges.

Sunday Morning Through The Afternoon

Increasing mid-high altitude clouds.  S-SW winds increasing to 5-15 mph, with higher gusts.  Temperatures varying from the mid 20s to low-mid 30s.  Wind chills in the 10s and 20s.

Sunday Night Into Monday Morning

Mostly cloudy.  Becoming windy.  Evening temp drop in sheltered valleys, then rising temps possible with mixing overnight into morning.  SSW-SW winds 10-20 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet.  SW winds 15-25 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures mainly in the 20s, except dropping into the 10s in sheltered valleys prior to rising by morning.  Wind chill factors in the single digits and 10s.

Monday Morning Through The Afternoon

Cloudy with snow, sleet, freezing rain-rain developing.  Icy conditions likely on many surfaces.  Windy.  SW winds 15 to 25 mph, with higher gusts ( decreasing beneath the top of any low-level inversion formation ).  Temperatures in the 30s, then dropping to around or below freezing within the SW upslope flow corridor along and southwest of the High Knob Massif-Tennessee Valley Divide as well as beneath any low-level inversion.  Wind chill factors in the 10s and 20s.  Dense fog formation possible.

A January thaw period next week is expected to give way to bitter cold once again by late next week-weekend ( January 12-14 period ) as the winter pattern locks back into the eastern USA.

Weather Discussion ( Nasty )

Early Overnight Monday Update

Strong-roaring SSW-SW winds are blowing across the high terrain in advance of developing precipitation downstream of the mountains.

Strong and gusty winds will continue to mix downward to below the 2700 foot level into middle elevations overnight into Monday morning.

Dry air in lower levels of the atmosphere may keep precip from reaching the ground until the mid-morning period, with evaporative cooling helping create a setting where various types of frozen precipitation will be likely.

The best chance for snow, with possible accumulations, will be within the SW air flow upslope zone from the Tennessee Valley Divide-High Knob Massif southwest into portions of Lee County where air flow becomes orographically forced.

Unless a strong inversion develops, limiting mixing, downslope flow could help reduce frozen amounts in the Pound-Clintwood to Haysi-Grundy zone; however, this is not a typical setting with all ground surfaces being frozen to increase the hazardous aspect with only light precipitation amounts.

Previous Discussion

Another bitterly cold night, especially in mountain valleys, will be observed into Sunday morning before conditions get nasty in another way.

The best radiational cooling conditions of this great cold wave to date will be observed tonight into Sunday morning, especially within mountain valleys where temps will again drop below zero ( far below in high elevation valleys where temperatures were already dropping to 0 degrees at 6 PM ).  Lower elevation valleys, like in Clintwood, with less snow cover were at 10 degrees at 6:00 PM Saturday.

Saturday ( January 6 )
MIN Temperatures

Nora 4 SSE
-1 degree

Clintwood 1 W
-5 degrees

City of Norton
-6 degrees

Black Mountain
-7 degrees

*The coldest temperatures occurred within the snow covered expanse of the High Knob Massif, which I will highlight later.

Low temperatures into Saturday morning were frigid from top to bottom, with most locations across Wise & Dickenson counties falling to 0 degree and below.

Saturday afternoon MAXS varied from 6 degrees on Eagle Knob of the High Knob Massif to 18 degrees in Clintwood.  No wonder high valleys have had such a quick drop toward zero degrees with cold air drainage from the summits, with the temp on Eagle Knob falling back to 0 degrees at 6:15 PM.

The main difference tonight versus last night being that temps will not drop a lot more on the summits, but will begin to rise into the overnight and morning hours of Sunday as high valley temps continue to drop.  A key factor to cooling being dewpoints within the 875-825 MB layer of the atmosphere for high country valleys surrounded by snow covered terrain.

After more than 40 years of recording mountain weather it has been learned well that coming out of a great cold wave is typically never easy, with strong winds causing low chill values being a typical ingredient having to be endured as baroclinicity increases ( horizontal temp gradient packs ) and generates a pressure gradient that cranks up strong winds to push against the mountains and drive the bitter air away ( an especially nasty process for everyone living within mid-upper elevations ).

Models will continue to struggle as they try to resolve what is going to happen with the vertical temperature profile in the atmosphere, but the fact remains they they simply will not be able resolve what 10-14 days of below freezing temps have done to surfaces ( freezing the ground deep ) which will not even begin to thaw prior to any precipitation.

An ice up on surfaces, a period of snow to mix, formation of fog over cold ground are all on the table, perhaps even more significant SW upslope flow snow, as the battle between warm air advection and arctic air develops Monday.

Roads treated with new cold weather solutions will certainly do better than many back roads and other surfaces which are not treated in such ways.  No surface; however, should be taken for granted and everyone will need to be on high alert Monday with respect to decks, walkways, roads, etc…until the icing threat passes. 

One aspect appears certain, given this great cold wave has not been just concentrated in the mountains, the typically milder domain of the Great Valley will also be subjected to potential chaos as this transition occurs.

Mountain Area Forecast ( Jan 3-5 )

ALERT For Bitter Cold During Thursday-Saturday With A Reinforcing Surge Of Continental Arctic Air – Expect The Most Severe Conditions Experienced So Far During This Cold Wave Of Late 2017-Early 2018

Bitter cold air and dangerously cold, life threatening wind chills will develop into Thursday-Friday as a large mass of cA ( continental Arctic ) air is pulled south across the region when the pressure gradient tightens around a deep cyclone in the western Atlantic Ocean.

ALERT For Whiteout Snow Squalls In NW Upslope Flow

*As of 5:30 AM up to 2″ of snow have already fallen in parts of the area, especially with persistent snowstreaks into upper elevations of the High Knob Massif from High Knob along Little Mountain.  Expect drifting at upper elevations due to strong NW winds.

Extremely bad conditions have developed along State Route 619 & Route 237, as well as other middle-lower elevation roads across Wise-Dickenson counties, with plunging temperatures.

Although big snowfall will remain near the Atlantic Coast, moderately strong NW upslope flow will carry enough low-level moisture south to produce accumulating snow along the upslope side of the Appalachians, with a general 1-4″+ currently expected in the favored orographic areas ( higher amounts may occur from the High Knob Massif northeast to Snowshoe-Canaan Mountain with squalls & snowstreaks ).  Roadways are expected to become slick.

Due to stronger winds during this period, versus the most recent cA blast, wind chills will be lower and conditions more dangerous over a prolonged period of time.

Overnight Into Wednesday Morning

Increasing high clouds.  Light winds becoming SW at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges.  Temperatures varying from 10s mountain ridges to single digits in valleys, except around or below zero degrees in colder mountain valleys.  Wind chills in the single digits above and below zero along higher mountain ridges.

Wednesday Afternoon

Partly-mostly cloudy ( high clouds ).  SW winds generally less than 10 mph.  Temperatures varying from upper 10s to lower 20s at highest elevations to the upper 20s to low 30s.

Wednesday Night Into Thursday Morning

Increasing clouds and lowering cloud bases overnight into morning with snow showers & flurries developing.  Winds shifting NW & increasing to 10-20 mph, with higher gusts, mid-upper mountain ridges and plateaus.  Turning colder with temperatures dropping into single digits to low 10s, except to around 0 degrees on highest peaks.  Riming at upper elevations, mainly above 3300 feet.  Wind chills from 5 above to -15 degrees below zero, except -15 to -25 below at elevations above 3300 feet.

Thursday Afternoon

Mostly cloudy.  Chance of snow showers, flurries and local snow squalls. Bitter. NW winds 10 to 20 mph with higher gusts.  Temperatures varying from 0 to 5 degrees along highest crest lines to the low-mid 10s ( milder south into river valleys of the Clinch, Powell, and Holston ).  Wind chills 5 above zero to -15 below zero at elevations below 3000 feet, -15 to -25 below zero chills above 3000 feet.

Thursday Night Into Friday Morning

Snow showers, flurries and local snow squalls.  Bitterly cold.  WNW-NW winds 10-20 mph, with higher gusts on mountain ridges.  Temperatures falling to 5 above zero to -5 degrees below zero, except colder on highest peaks.  Wind chills 0 to -20 degrees below zero, except -20 to -30+ degrees below zero highest elevations.  Rime formation in super-cooled orographic clouds at upper elevations.

Snowfall Forecast – Thursday AM Through Friday AM

General 1″ to 4″ along the upslope side of the mountains, with higher amounts possible in the High Knob Massif and within other most favored high mountain areas. 

The potential for extremely slick conditions are being monitored by early next week as a mix of precipitation falls upon surfaces frozen by prolonged sub-freezing temperatures.

Weather Discussion ( Harsh Period )

Early Thursday Evening Update

Light snow, flurries, and locally heavier snow showers are continuing across the area and will persist as the low-level moisture increases into overnight as the 850 MB thermal MIN ( coldest air ) pushes into the mountains.

A slick and snowy overnight-morning ruled the area with widespread snow accumulations in NW upslope flow from northern Lee and northern Scott counties across Wise and Dickenson counties into Buchanan County.

Snowfall accumulations varied from around 0.5″ on the low end to widespread 1-2″ ( Pound, Norton-Wise, Clintwood ) upward to between 3-4″ ( High Knob-Little Mountain area ).

It was a classic NW flow setting with simply gorgeous mountain waves forming from the Cumberland Overthrust Block ( where the first true mountains rise to perturb air flow ) southeast to where visible waves dissipated leeward of the Blue Ridge.

A larger-scale view revealed snow on the ground toward the Atlantic Coast beneath clearing skies with subsidence in the wake of intense western Atlantic cyclogenesis and sinking air lee of the Appalachians.

Bitter cold has made this a nasty event, with ”warmest” temperatures occurring at the very beginning of January 4.

Joe & Darlene Fields measured 2″ of snow in the High Chaparral community into Thursday morning, with heavier 3″+ depths toward the Little Mountain-Cox Place communities.

Afternoon MAX temperatures varied from 3 degrees on Eagle Knob to 16 degrees in Clintwood.  The problem, it never felt that warm!

A max of 4.7 degrees was recorded by the Black Mountain mesonet, with wind chills as low as -22 degrees below zero during the day.

This was especially true at middle-upper elevations where 20-30+ mph wind gusts were common.

 Please use extreme caution if needing to be outdoors.

Previous Discussion

Following a Tuesday morning MIN of -3 degrees below zero in Clintwood the afternoon MAX reached 23 degrees, then fell back to 2 degrees by 2:00 AM Wednesday.

Temperatures have been much colder in snow covered upper elevations of the High Knob Massif, with colder valleys quickly dropping back to below zero Tuesday night beneath clear skies before increasing high clouds-winds stopped the plunge. 

Increasing high altitude clouds overnight into Wednesday is a signal of the upcoming weather change that will again feature a huge surge of bitterly cold air.

Although bitter cold will be the big weather story again, the development of NW flow snow showers, flurries, and snow squalls should not be overlooked with slick road conditions developing within favored upslope locations along & north of the High Knob Massif-Tennessee Valley Divide, and in a narrow zone from Mount Rogers-Whitetop southwest along the TN-NC border toward the summit level of the Smokies.

A stronger and somewhat more cyclonic flow will help orographic forcing to be stronger than the previous blast, when up to 1″ or so of snow accumulated at the summit level of the High Knob Massif ( on meager moisture-lift ).

Reference my 123117 Forecast for details and photographs.

Bitter air = very low snow density and much greater amounts than 10:1 model ratios are predicting with orographic NW upslope flow given any moisture.

*If the western Atlantic low pressure tracks closer to the coast, and the pressure gradient is stronger than currently forecast, upslope snowfall amounts along the Appalachians will trend greater than I am currently forecasting.

Wind chills are going to be a major factor during the Thursday-Saturday period and models are too course to accurately resolve true chills amid complex terrain, so it is hoped that NWS Forecast Offices will post an advisory or warning for all of the mountain area.

With more snow expected along the upslope side of the mountains, an enhancement of bitter cold temperatures will help make this blast worst than the previous event.