My Forecast For Today ( February 25 )

ALERT For Accumulating Snow Mid-Upper Elevations Into Thursday Morning ( Mainly At Upper Elevations During The Day ) And Across All Elevations Along The Upslope Side Of The Mountains ( WNW-NW winds ) During Thursday Night Into Friday Morning

This Will Be An Elevation Biased Snow Event Until Thursday Night, When All Elevations Will Have The Best Chance For Accumulating Snow & Widespread Hazardous Travel Conditions.

As of 11:00 PM Wednesday State Route 619, Routes 237 & 238, as well as others, at upper elevations in the High Knob Massif, were becoming icy and snow covered.  Sticking snow levels will drop to around 1300-1700 feet by morning, then be mostly at elevations above 2500-3000 feet during the day before dropping to include the entire area along the upslope side of the mountains during Thursday Night into Friday morning ( * ).

*The GFS Model is colder on Thursday than the NAM Model.  If the GFS verifies then sticking snow levels during the day will remain lower and generally be at or above 2000 feet ( lower amid any squalls ).

Due to strong upslope flow there will be a tendency for sticking snow at lower elevations along and southwest of the High Knob Massif and Tennessee Valley Divide ( 1300 feet ), than for lower elevations northeast-east of this high terrain ( 1700 feet ), into Thursday AM ( this morning ).

*Any snow squalls that may develop today could cause sticking and low visibility at any location, with subsequent melting & sunshine due to sinking air in their wake.

Overnight Into Thursday Morning

Any rain-sleet showers changing to snow showers. Blowing snow ( heaviest snow and best sticking along and southwest of the High Knob Massif-Tennessee Valley Divide at 1300-1500 feet or higher in elevation ).  Windy.  SW to W winds 15-30 mph, with higher gusts.  Temperatures varying from 20-25 degrees at upper elevations to the lower-middle 30s.  Wind chills dropping into the 10s and 20s, except 0 to 10 degrees along upper elevation mountain ridges.

Snow which sticks into Thursday morning may tend to melt at lower and middle elevations during the day, especially in places with southern exposures and during any hazy sunshine or breaks in the overcast ( even upper elevations will tend to have melting, especially across southern exposed slopes ).

The exception to the above will be northern slopes, especially at the higher elevations, and any place having a snow squall ( burst of heavy snow ) which could cause local sticking and significant reduction in visibility for short-periods of time.

This Afternoon

A chance for snow showers & periods of snow at mid-upper elevations, with a mix possible at lower elevations ( below 2000 ft ).  Local snow squalls ( bursts of heavy snow ).  Some breaks in the overcast possible.  Windy.  Winds W-WNW 10-25 mph, with higher gusts.  Temps from mid-upper 20s at upper elevations to the mid-upper 30s.  Wind chills in the 10s & 20s ( locally colder in gusts at highest elevations ).

The most snowfall, and most widespread sticking with hazardous travel, is expected to develop Thursday evening into Friday AM.

Tonight Into Friday Morning

Snow showers & snow squalls.  Snow may be heavy at times.  Windy with blowing snow ( especially along exposed mid to upper elevation mountain ridges & plateaus ).  NW winds at 10-20 mph, with higher gusts.  Temperatures varying from the low-mid 10s at highest elevations to the mid-upper 20s  ( milder at lower elevations toward the Tri-Cities ).  Wind chills varying from single digits below & above zero at the upper elevations to the 10s to lower 20s.

Weather Discussion ( February 24-25 )

My Afternoon Update

Following some good overnight-morning snow a break with flurries and scattered, mostly light snow showers, has been the rule during the early-mid afternoon.

At 9:00 AM my friend Joe Carter, of the City of Norton Water Plant, measured 1.5″ of snowfall ( between 1-2″ on ground ).  Since then there has been little additional sticking.

The City of Norton Water Plant reports 6.85″ of precipitation for the month of February ( 2.39″ with this storm event ), with 11.08″ since the beginning of 2016.

A general 2″ to 4″+ of snow depth is on the ground on Eagle Knob this afternoon, with around 3.0″ of snowfall being the estimate for the wind driven overnight & morning fall.  The temperature on Eagle Knob has held steady or slightly fell amid lower 20s during the day ( wind chills have, of course, made it feel much colder in all locations today ).

My friend Darlene Fields measured 2.3″ on the ground at 5:10 PM in High Chaparral ( around 2.5″ or more of total snowfall with some settlement today ).  This has, of course, been a difficult snow to measure given ROARING winds and by the end will require more figuring ( to figure it out )!

To the north, at Clintwood 1 W, I had just under 1.0″ of snow this morning which has now nearly all melted away with 35 degrees.

Flurries and light snow showers occurring now are due to a shift to more mid-continental air, with the 1:00 PM analysis from the NAM 12 KM Model showing this well.

*The NAM Model ended up beating the GFS Model on afternoon coverage, but temperatures on the GFS Model have been closer to reality than those predicted by the NAM.  Yet again this illustrates that no model is correct, with forecasters needing to follow actual conditions, use past climatology of similar conditions, and try to use the model, or blend of models, that fits the setting best.

ALWAYS keeping in mind the known model biases which research by Baker & Konrad clearly show places too much emphasis on locations near the ECD ( Eastern Continental Divide ) relative to the western front range of the mountain chain ( likely the largest model errors in all of the southern Appalachians, according to my data, is centered upon the High Knob Massif where much more snow falls than is forecast by computer models on NW Flow & other flows ).

Graphic Above Courtesy of: Relationships between NW flow snowfall and topography in the Southern Appalachians, USA by authors L. Baker Perry and Charles E. Konrad.

Forecast models consistently under-estimate snowfall along the western front of the southern Appalachians, with largest model errors showing up on Mount LeConte, Wise, and Beckley.

Forecast models consistently over-estimate snowfall along the ECD from Virginia down along the TN-NC border ( except for the highest peaks ) during NW Flow events.

If observed snowfall in the High Knob Massif ( e.g., High Chaparral and the main crest zone ) was factored into this it would easily be the largest under-estimation in the southern Appalachians.

Yet most forecasters, unaware of this research and my 27 years of collecting snowfall, including the Weather Channel, consistently neglect this research and place heaviest snow amounts along the ECD indiscriminately ( including places like the New River Valley and many sites along the NC side of the border where snowfall tends to be much less during many such events ).

*I grew up watching The Weather Channel always place a strip of heavier snow down along the ECD to the east of Norton-Wise and Clintwood.  I said, “that just doesn’t look right to me.”  I started measuring snow when I was just 10 years old and began to see it was not right.  Wise, officially the snowiest Town in Virginia, was always being left out ( in the cold )!

Due to abundant mid-level moisture there have been no breaks in the overcast to make the lower-levels more unstable, limiting heavier snow showers and squalls.

An upper wave approaching will help turn the low-level flow back off the Great Lakes tonight into Friday morning.

This will increase snowfall again as the coldest temps this system offers move into the mountains on NW upslope.  I expect hazardous travel conditions to become widespread along the upslope side of the mountains into Friday AM.

A general 1″ to 3″ of new snow, with locally more possible atop the High Knob Massif, will put event snowfall totals into ranges that I originally forecast a couple days ago.

My Overnight Discussion

Reference my 022416 Forecast & discussion for more details on this past day of turbulent weather conditions.

Yet another phase of a powerful late season winter storm has now been entered, with complexity remaining in the forecast for today into Friday.  I have tried to condense it above, with emphasis on this being an elevation biased snowfall event through today ( i.e., better sticking-snow with increasing elevation through today ).

Observe temperature changes which occurred today…between 7:00 AM and 7:00 PM…as this monster-sized storm swirled across the region, triggering a Tornado Outbreak in eastern Virginia.

A deadly and destructive tornado outbreak in eastern Virginia.

Observe the 850 MB wind field changes between 7 AM and 7 PM.

Colder air has been driven into the area on SW winds.

At Midnight, for example, roads & the ground are covered atop the High Knob Massif while nothing has stuck at my official NWS station in Clintwood ( with wind driven sleet being the main precipitation type during the evening ).

*The Midnight temperature was 24 degrees atop the High Knob Massif with wind chills in the single digits.  By contrast, the air temperature was 36 degrees in Clintwood.

There is a natural tendency, due to strong upslope flow, for sticking to occur at lower elevations along & southwest of the  High Knob Massif & Tennessee Valley Divide on SW-WSW flow through the overnight into Thursday morning than for locales northeast-east of this high terrain.  This is exemplified at the present time by differences between Jonesville & Birchleaf:

Jonesville & Birchleaf are both close to the same elevation above sea level, but strong SW upslope flow is making the air cooler in Jonesville ( 32 degrees ) than Birchleaf where SW air flow sinks and warms into the Russell Fork basin.  The midnight temp in Clintwood was also 36 degrees.

Today the atmosphere becomes more unstable as temp drops with height increase.  Although the NAM Model is actually not forecasting any snow to fall this afternoon, that seems unlikely given enough moisture to generate snow showers and some hit or miss snow squalls ( as the atmosphere gets more unstable the chance for developing bursts of heavy snow will increase in a hit-miss fashion ).

Air tends to converge into snow squalls and snowstreaks and to subsequently sink ( as demanded by atmospheric compensation ) around their peripheries.  Sinking air opens up clouds to sun that then acts to make the lower atmosphere more unstable, forming a feedback cycle that then feeds upon itself to help develop more snow squalls and/or streaks.

*Since the 850-700 MB flow will become unidirectional this also increases the chance for snowstreaks ( a train of squalls ) to form today as flow comes south off the Great Lakes.  Any places having a snow squall, or snowstreak, could accumulate snow during the day while in general the best sticking today will be at highest elevations and northern exposed locations.

By this evening into Friday morning conditions begin changing as the coldest air this system has to offer is transported into the mountains ( 850 MB thermal MIN ), along with a period of deep moisture & upper divergence which is joined and followed by good NW Upslope Flow.  Therefore, the most snow and best accumulations will become most likely tonight into Friday morning.

*Some places may have little to no snow accumulation until this period ( Thursday Night into Friday Morning ).

Nice diffluence aloft at 500 MB and PVA will be beneath good speed divergence at 300 MB.

Combined with excellent NW upslope flow and moisture from Lake Michigan the stage will be set for accumulating snow showers, squalls, and maybe some streaks.

The Thursday evening through Friday morning period should produce the best ( most ) snowfall of this event, along with the most widespread hazardous travel.

*There is an excellent chance for many more school schedule changes Friday than into this morning ( Thursday ).

Make it a great Thursday.

My Forecast For Today ( February 24 )

ALERT For A Major Winter Storm Impacting The Mountain Region Wednesday-Friday Morning With Strong Winds, Rain, Possible Thunderstorms, And Significant Snow-Rime At Mid-Upper Elevations

The General Order For This Event

Rain showers & rain increase during the overnight.  Downpours will become possible, especially along upslope favored locales on SE to SSE winds.

Wind speeds increase at mid-upper elevations with potential for mountain wave development and impacts in valleys leeward of the High Knob Massif, Clinch Mountain, Pine & Black mountains in the overnight-morning hours of Wednesday.

A broken or solid line of downpours, with possible thunderstorms, is roughly timed to arrive from southwest to northeast during the sunrise to mid-day period ( around 8-9 AM for Norton-Wise ).

Any break then gives way to redevelopment of showers, with possible downpours ( thunder can not be ruled out ) along and just ahead of the surface cold front during Wednesday afternoon.

A sharp temperature drop occurs as winds become very strong and gusty ( ROARING ) across the area between 4:00 PM and 7:00 PM as the cold front passes.  I can not STRESS ENOUGH that WINDS Will ROAR along and behind this cold front.

Rain showers change to wind driven snow by late afternoon into the evening for locations along the Virginia-Kentucky border, with sticking starting first at highest elevations and working downward into middle-lower elevations over time.

Significant snow ( with riming in upper elevations ) is expected Thursday-Thursday Night into the predawn hours of Friday for middle-upper elevations.

Threat for severe thunderstorms remains relatively low, but shear will be so strong that a severe thunderstorm can not be ruled out ( with increasing threat for severe storms across central-eastern Virginia into the Carolinas today ).  

Due to such strong gradient winds and shear the main threat today, whether with thunder or not, remains wind damage for all locations in the mountain area.  This raises the potential for power outages and local tree damage.

Reference my 022316 Forecast for details which remain valid.

Overnight Into Mid-Morning Wednesday

Rain showers.  Becoming very windy along middle-upper elevation mountain ridges ( and in mountain wave zones ).  Downpours possible, with a chance of lightning-thunder into morning.  SE-SSE winds increasing to 10-25 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet.  SSE winds 20-35 mph, with gusts 40-50+ mph, on upper elevation mountain ridges.  Unseasonably mild with temperatures in the 40s to middle 50s.

Mountain waves will become possible into Wednesday morning, with strong to locally severe wind gusts in favored breaking zones from Powell Valley in Wise County to the Clinch Valley of Russell-Tazewell counties ( and immediately next to the Kentucky side of Pine Mountain and Black Mountain ).  Some questions remain as to how an atypically low inversion level will impact these waves.

Due to 1.00″ to 1.50″ of rain during the past couple of days, any prolonged moderate rain or downpours will need to be respected through today until colder air arrives ( ponding of water in low lying and poor drainage areas, rises on streams, will need to be followed closely until after the cold front passes ).

A dramatic weather change will occur this afternoon along and behind a strong cold front, with ROARING winds as a very strong pressure gradient begins driving and funneling SW flow upslope through the High Knob Landform into the Norton-Wise area and adjacent locations.  This will be the windiest period for the entire area as a whole, with strong winds extending into the evening.

Mid-Morning Through This Afternoon

Showers redevelop following any brief break.  A chance for downpours.  Thunder possible.  ROARING WINDS develop in all locations along and behind a strong cold front.  Showers of rain change to snow late.  Winds shifting SSW-SW at 20-40 mph, with higher gusts.  Temps plunge from the 50s to around 60 degrees into the 30s to around 40 degrees by sunset to early evening.  Wind chills dip into the 20s.

Blowing snow and drifting will develop overnight into Thursday amid upper elevations in the High Knob Massif, along with rime formation at elevations above 3000 to 3500 feet.

Tonight Into Thursday Morning

Any rain showers changing to snow showers during the evening.  Snow overnight, heavy at times ( especially along and southwest of the High Knob Massif & Tennessee Valley Divide ).  Windy.  SW to W winds 15-30 mph, with higher gusts, at elevations below 2700 feet.  SW-W winds 20-35 mph, with higher gusts, along upper elevation mountain ridges.  Temps varying from lower 20s to lower 30s by morning ( coldest at highest elevations ).  Wind chills dropping into 10s & 20s, except single digits at high elevations in the High Knob Massif.

Snowfall Forecast For The February 24-26 Period

Target Snowfall of 4″ in Norton-Wise ( +/- ) 1.5″ Spread Potential.  This implies snowfall totals from 2.5″ to 5.5″ will be possible with variations expected on the ground due to an unfrozen, wet state day-time settlement-melting, and blowing by strong winds.

A general 4″ to 8″ of snow is expected above 3000 feet amid the High Knob high country, with locally higher totals possible.  Large ground depth variations are expected due to blowing and drifting at the highest elevations ( with significant rime formation ).

*In general this is expected to be an elevation biased event, with increasing snow depth with increasing elevation.  Snow squalls and/or snowstreaks that may develop Thursday could locally skew this general trend.

Weather Discussion ( February 23-24 )

Late Afternoon Update

It has been quite a weather day across the mountain area, with ROARING winds and ROARING water.  As of 6:00 PM it has gotten cold enough for the first flakes of snow to begin falling atop the High Knob Massif ( at summit levels ).

However, most of the snow will begin to come in later during the evening and into the overnight period and Thursday morning.

Meanwhile, it is very dangerous around trees as gusts are making them pop and crack.  I was just outside to hear it first hand, so please use caution in these high winds.

The only update to my forecast late this afternoon being to ease wind speeds up even more, than I had them before, for tonight.

Sustained winds between 20 and 30 mph have been common at middle to upper elevations this afternoon, with gusts topping the 50 mph barrier atop the High Knob Massif and Black Mountain.

Outside of any mountain wave gusts and roaring winds along high mountain crest lines, the real ROAR began in most places along and behind a mid-morning squall line with heavy rain that passed through the Norton-Wise & Clintwood-Pound area during the 9:15-10:15 AM period.

Winds have truly been a ROAR with many twigs, limbs, and other debris scattered across the area, including some trees.  Power outages have so far been localized ( thankfully ).

More than 1.00″ of rain since Midnight, upon already wet ground, has pushed steep creeks draining the High Knob Massif into a pounding ROAR.

As of 3:15 PM the Big Stony Creek stream gage showed the level was just 14″ below flood stage.  Similar conditions are occurring on South Fork of the Powell River and adjacent steep creeks from Clear Creek to Little Stony Creek.

With colder air now pouring into the mountain area, and showers of rain that will change to snow tonight at mid-upper elevations, these high stream levels should gradually drop ( but please use caution around these creeks and their slick-rocky banks ).

My Overnight Discussion

A beautiful array of mountain wave clouds developed along the High Knob Massif during Tuesday afternoon, even if the high winds aloft had not yet reached the surface in valleys.

I have labeled a few views to illustrate the different types of orographic clouds being generated.

It was magical to watch how the massif interacted with air flow to generate these magnificent clouds ( these views not doing them justice, as would seeing them via your eyes ).

While some clouds changed continuously with air flow rushing over the massif, other clouds held their forms and were long-lived in nature ( e.g., the orographic cap cloud mass and standing wave cloud which varied little in position over time ).

Observe the long-tail which developed around sunset on the wave cloud capping the massif ( below ).

This cloud later developed a fish-tail form, and it was a shame to see darkness fall with such beautiful wave clouds taking on these majestic shapes.

The CAM switched into IR Model for better night vision.

Focus now shifts to a powerhouse winter storm system that will impact weather into Friday.  Models have not changed much locally from what I highlighted in my discussion last night, with an increasing risk for severe thunderstorms and possible tornadoes from central-eastern Virginia south into central-eastern portions of the Carolina’s.

However, this area will have to closely watch a squall line of downpours ( with possible thunderstorms ) that is currently timed to move across far southwestern Virginia during the 7:00 AM to 10:00 AM period.

The 1:00 AM run of the High-Resolution Rapid Refresh ( HRRR ) Model has the squall line over Norton-Wise at 9:00 AM.  Timing could, of course, be off some but this is the current trend.

Downpours of heavy rain and strong to potentially severe gusts of wind will have to be watched for during this time given such strong winds roaring across the high mountain summits ( and aloft ).

There remains a period today when models want to allow some surface based convective available potential energy, called SBCAPE, to develop amid still strong shear.

It is the lack of instability through this morning that will greatly limit the severe potential ( and a inversion layer aloft ) relative to what it would be with this ( below ) if significant instability was present to form surface based convection ( which in this type of high shear environment would easily be capable of developing rotating updrafts ).

Shear and the magnitude of helicity relative to how a storm updraft could be driven to rotate becomes simply extreme by the predawn-morning hours of today, but instability is lacking ( thankfully ).  Still this does not rule out a severe thunderstorm developing into this morning and will tend  to increase the risk of strong-severe winds along a squall line which may move across the area this morning.

Models say that the southern portion of the Tennessee Valley will have the greatest severe thunderstorm potential heading into this morning, with the best overlap of shear and instability.

As time passes, we will have to see if this potential may work northeastward up the Great Valley and into the Mountain Empire in advance of the surface cold front to provide one more period where severe thunderstorms ( outside any morning squall line ) and/or severe downdrafts in showers will be possible.

Clearly the best overlap of shear and instability will be developing east of the mountains by later this afternoon-evening into central portions of Virginia & the Carolina’s.

A severe outbreak could develop there as snow begins to fall atop the High Knob Massif, which, by no coincidence, has happened during past events as well documented by climatology.

One change from yesterday is that models are a little faster in bringing in the cold air, with the 0 degree ( 32 F ) freezing line overspreading far southwestern Virginia between 4 PM and 7 PM, on simply ROARING SW winds along and behind a strong cold front.  It would not be impossible to go from rain & thunder to snow in just a short time.

From this point onward it will be all about the wintry side of this storm system, with strong orographic forcing continuing into the Thursday Night-Friday AM period.  The flow being better for the City of Norton to get more snow than Wise, but time will tell about that ( as regards Norton vs. Wise snowfall totals ).

Stay tuned to NOAA weather radio for any possible warnings that may be needed through today.

Make it a great Wednesday.

My Forecast For Today ( February 23 )

ALERT For A Major Winter Storm Impacting The Mountain Region Wednesday-Friday Morning With Strong Winds, Rain, Possible Thunderstorms, And Significant Snow-Rime At Mid-Upper Elevations

Overnight Into Tuesday Morning

Rain developing.  Becoming steady and soaking into the overnight, especially along and southeast of the VA-KY border.  Winds becoming ESE to SSE at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges.  Temps widespread in the 40s ( dense fog developing in upper elevations – patchy fog in other locations ).  Wind chills in the 30s along upper elevation mountain ridges.

This Morning Through This Afternoon

Mostly cloudy.  A continued chance for rain showers.  Winds SE-SSE at 5-15 mph, with higher gusts, below 2700 feet.  SE to S winds 10-20 mph, with higher gusts, on upper elevation mountain ridges.  Temperatures widespread in the 40s to lower 50s.  Areas of dense fog possible, especially along high mountain ridges.

Mountain waves will become possible Tuesday Night into Wednesday morning, with strong to locally severe wind gusts in favored breaking zones from Powell Valley in Wise County to the Clinch Valley of Russell-Tazewell counties ( and immediately next to the Kentucky side of Pine Mountain and Black Mountain ).

Tonight Into Wednesday Morning

Rain showers.  Becoming very windy along middle-upper elevation mountain ridges ( and in mountain wave zones ).  Downpours possible, with a chance of lightning-thunder overnight into morning.  SE-SSE winds increasing to 10-25 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet.  SSE winds 20-35 mph, with gusts 40-50+ mph, on upper elevation mountain ridges.  Unseasonably mild with temperatures in the 40s to middle 50s.

A squall line of rain, with embedded thunderstorms, will be possible early Wednesday well in advance of an approaching cold front.  Instability during the afternoon may aid formation of low-topped convection, with northeast movement through the Great Valley toward the Cumberland Mountains along this cold frontal boundary.  The greatest threat will be potential for wind damage.

Given recent wetness, and Winter 2015-16 wetness in general, any moderate to heavy rainfall will be capable of causing strong rises along creeks as well as ponding of water in poor drainage and low lying locations during Wednesday.

A sharp temperature drop will follow with rain changing to snow during Wednesday evening in upper elevations of the High Knob Massif.  Snow levels will drop in elevation into Thursday AM.

Significant snow accumulations will be possible at mid-upper elevations during the Wednesday Night-Friday Morning period, with preliminary snow totals of 3″ to 5″ in the Norton-Wise area, 4″ to 8″ in the High Knob Massif ( above 2700 feet ), and 1″ to 3″ amid lower elevations around Pound, Clintwood & Clinchco.

Stay tuned for later updates. 

Weather Discussion ( February 22-23 )

Monday ended up being the best day of this work week to come, with lifting of cloud bases and gloomy but rain free skies as temperatures ranged in the 40s to middle 50s.

Rainfall totals of 0.70″ at the City of Norton Water Plant and 0.64″ in Clintwood were measured Sunday into early Monday morning.

A lead wave is spreading a steady, light to moderate rain across the mountain area tonight well in advance of the main system developing over Texas ( the big storm ).

Models had initially predicted rain tonight to remain mostly southeast of the area; however, a progressive northward shift will now allow for the most widespread, steady rain to fall along and southeast of Pine Mountain of the Cumberland Overthrust Block.

This rain will further saturate an already soggy ground to make water level rises with the main system on Wednesday potentially more problematic than if today had remained dry.

Focus now shifts to the main storm event.

Exceptional storm relative helicity, driven by strong wind shear, will be in place early Wednesday as showers & storms develop.  This will need to be closely watched despite a lack of any SBCAPE ( surface-based convective energy ).

SBCAPE = Surface Based Convective Available Potential Energy

An idea of the wind shear driving the strong SRH values can be obtained by looking at the cross-over flow in the vertical ( surface-850 MB-500 MB vectors overlaid ).

Both speed + directional shear in the vertical is acting to drive these extreme storm relative helicity values ( above ).  Superimposed upon this setting will be a mountain wave formation potential in breaking zones.

One of the interesting aspects of this storm event is that height falls will be so significant that the 850 MB level will actually drop down below the summit level of the High Knob Massif for a time.  The inversion level above is very low and it will be interesting to see how this may impact mountain wave formation.

Heights refer to the level of a particular isobaric surface, such as the 850 MB level.  It is typically around or just below 5,000 feet.  In this case, it will be dropping down to around the 4,200 foot level of the High Knob Massif.  That tends to indicate a very strong storm system developing, with falling heights indicative of large changes in mass within a vertical column of air.

Since warm air advection will be occurring against these height falls it means that the warm advection is being mostly applied to upward vertical motion, or large-scale lift.  Otherwise, the WAA would act to pump up heights and raise them to higher levels.

During Wednesday afternoon the SRH values begin to decrease amid the warm sector ( remaining very high within the most stable wedge zone with CAD to the east ).

SRH = Storm Relative Helicity

CAD = Cold Air Damming

There remains a notable gradient in the High Knob Massif, northeast Tennessee Valley zone, that needs to be watched.

The difference is models are showing some 500-1000 J/Kg of surface-based CAPE, which could generate low-topped convection with a wind damage potential ( as climatology during past such settings would suggest ).  This will need to be closely followed through the day on Wednesday.

CAPE = Convective Available Potential Energy

During this time period an inverted-V type of low-level sounding is suggestive of a marginal tornado risk, or brief spin-up, should this SBCAPE actually develop ( this will be more likely should breaks develop in the overcast to allow surface heating in between rain showers ).  Otherwise, beneath solid overcast this risk would remain minimal.

The current Storm Prediction Risk regions up to 7 AM Wednesday ( February 24, 2016 )

The main risk region for severe thunderstorms is forecast to shift east of the Appalachians through Wednesday into early Thursday.

The cold side of this storm begins Wednesday evening as rain changes to snow from top to bottom over time, with early evening featuring a change at the High Knob Massif summit level as cold air surges quickly in from the SW.

Moisture remains deep from the surface up through 700 MB to signal that significant snow will be likely, with a notable Lake Michigan connection currently being forecast.

I show the 700 MB RH and Flow Charts since 925-850 MB moisture remains copious = great moisture for snowfall production as was observed during much of the January 2016 storm event ( although snowfall amounts this time will be much less but still productive ).

In this case the 700 MB moisture field being especially important since it will maintain dendritic crystal growth as moisture reaches into -12C air or colder ( in this case that would not occur if the 700 MB moisture was not present since the summit level pilatus cloud temperatures reach only around -10 C at the end of this event ).

Reference The Physics Of Snow Crystals for more information.

Due to the thermal structure the best snow accumulations will occur across middle-upper elevations above 2000 feet, with heaviest snow likely above 3000 feet in the High Knob Massif where excellent orographic forcing and exposure will exist during this event.

Orographic Forcing = not only wind speed + direction but many other factors such as moisture and riming of snowflakes which increases snowfall volume, massif width which enhances snow amounts as well & tends to reduce carry-over to lee side valleys

This will again be a setting where more snow is likely to fall and accumulate on above ground objects than the ground, with depths being less than the total snowfall outside of drifting amid upper elevations, where wind blown snow and riming will be factors.

Lower elevations, below 2000 feet, and especially those downslope of the mountains will have a harder time accumulating snow in daylight hours ( best opportunities being after darkness falls ).

Make it a great Tuesday.

My Forecast For Today ( February 22 )

The Alert for Dense Fog has been cancelled due to drier air working into the lower-level northerly flow today.  Lowering clouds again are likely into this evening with a chance for some showers.

Overnight Into Mid-Morning Monday

Rain & showers tapering to drizzle.  W-WSW winds 5 to 15 mph, with higher gusts, shifting NNW to NNE.  Cloud bases dropping to obscure middle elevations in dense fog.  Temps dropping into the upper 30s to middle-upper 40s by morning ( coldest at the highest elevations ).

Mid-Morning Through This Afternoon

Mostly cloudy ( cloud bases may lift off middle elevations ), with a few breaks possible.  Light N-ENE winds at generally less than 10 mph.  Temperatures varying from low-mid 40s to the low-mid 50s ( coolest at highest elevations ).

*High-resolution Models continue to ease the rain shield farther north and northwest tonight, such that I have updated again for the widespread development of rain ( steady, soaking rainfall ).

Tonight Into Tuesday Morning ( Updated 8:00 PM )

Rain developing.  Becoming steady and soaking into the overnight, especially along and southeast of the VA-KY border.  Winds becoming ESE to SSE at 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges.  Temps widespread in the 40s ( dense fog developing in upper elevations – patchy fog other locations ), with some upper 30s to near 40 degrees atop the High Knob Massif.

A Major Winter Storm system will impact the mountain region during the February 24-26 period with strong winds, rain and a potential for significant snowfall.  Preliminary indications for heaviest snowfall amounts are at middle-upper elevations from Wednesday Night through Friday ( starting at highest elevations with snow levels dropping over time ) on SW to W-NW winds.

Low pressure will intensify & become very strong as it moves from Texas toward New York State and the eastern Great Lakes between Tuesday AM and Thursday AM.  Multiple facets with this powerful winter storm system include strong winds ( with mountain wave formation possible on SE-SSE flow ), heavy rain, and a transition to snow in the backside circulation.  No snowfall amounts have been forecast yet, and the “Major” aspect is due to this being the winter season with a potent low pressure formation, so yes, any way this is dissected, it will be a Major Winter Storm System.  Details are yet to be worked out, including specific snow amounts.  Stay tuned.

Weather Discussion ( February 21-22 )

Mid-Morning Update

A look at low-level moisture this morning reveals that drier air has worked into the area northwest of last night’s front, and my update is to cancel the dense fog advisory.

Dissipation of low clouds has locally occurred to actually reveal summit levels of the High Knob Massif at 10:28 AM ( above ).

A look at the NAM Model sounding above Wise at 7 AM found most of the vertical column to be unsaturated, except right at the surface which has now been able to mix out.  An array of mid-high clouds remain aloft.

While cloud bases will drop again by this evening, with luck this will offer some breaks for hazy sunshine and somewhat milder PM temperatures that may break above 50 degrees at lower-middle elevations ( I have opened the range a little ).

The latest stream level shows that steep creeks continue to gush with whitewater this morning in wake of recent snow melt and rainfall, with Big Stony Creek being near the 4.0 foot RED Alert Stage.  While levels should begin to drop by later today, caution is advised around slippery-rocky banks of these roaring creeks.

My Overnight Discussion

A damp and gloomy Sunday graced the mountains with rumbles of thunder, to boot, well in advance of a frontal boundary that is just now pushing across the Virginia stateline at 12:10 AM ( February 22 ).

An old mountain saying states…if it thunders in February it will frost on the same day in May!  So mark that down now, and time will tell how close it is to reality this year.

Upper elevations in the High Knob Massif have been amid the clouds for the better part of 30 hours now, with many more hours to go before this dense fog will clear for any prolonged period of time.  High-resolution models are somewhat less aggressive in holding moisture in today, with only shallow moisture available that might have, given some luck, a chance to break up for a while.

A problem, of course, in telling exactly how today will play out arises since this frontal boundary stalls out over the mountain region today.  One reason model runs tonight are a little milder than last night with the boundary barely clearing the High Knob Massif area into this afternoon ( being just east-southeast ).

The big show, of course, that will dominate this week will be an intense low pressure that rapidly deepens ( gets strong ) as it lifts out of Texas into the Ohio Valley.

This will be one of the strongest storm systems of the entire winter season, and presents classic formation.

Doing some old school hand analysis, the phasing region for intense cyclogenesis really shows up well at 300 MB by 7 AM on Wednesday, with coupling between the Left Front Exit region of a Sub-tropical Jetstreak & the Right Rear Entrance sector of a Polar Jetstreak.  Large-scale divergence aloft will be evacuating mass, which by atmospheric compensation is replaced by inflow of air at low-levels where convergence and spin-up occurs amid intensifying low pressure.

The Interaction of Jet Streak Circulations during Heavy Snow Events
along the East Coast of the United States
LOUIS W. UCCELLINI AND PAUL J. KOCIN

For those wanting to learn more about how this works, the classic winter storm generation paper by Louis Uccellini and Paul Kocin from back in 1987 is a good point to start.

Uccellini, L.W., and D.R. Johnson, 1979: The Coupling of Upper and Lower Tropospheric Jet Streaks and Implications for the Development of Severe Convective Storms.  Mon. Wea. Rev. 107, 682-703.

The isallobaric component of this ageostrophic wind equation, above, which I mathematically derived from scratch some time ago is an important part of driving this:

This monster winter storm system is going to become a wind machine, which means orographic forcing is going to crank ( remembering with forcing there is both positive and negative forcing generated ).  The setting above, being for a strongly positive Mountain Torque force as the mountains push back against the atmospheric wind field.

Cold air surges in from the southwest with rain changing to snow at higher elevations Wednesday Night.  Given plenty of low-level moisture and strong forcing there is no doubt significant snow will fall across upper elevations in the High Knob Massif with winds also later shifting W-NW.

If this low had tracked farther south and eastward, instead of west and northwest, it would have been like the February 1985 Blizzard which required my friend Carl Henderson of Wise to be air lifted off Eagle Knob of High Knob after the storm ended.

*The late Carl Henderson was an electrical engineer at the Blue Ridge Public Transmitter Station on the summit.  Carl was a wonderful person and luckily had snowshoes, which he wore to reach a clearing where an Apache-Jet Helicopter landed to pick him up.  The extraction was needed since Carl was a diabetic and running out of medication ( plus he was also getting cold with minimal heat in the building ).  I’ve written about his adventure, which also was documented by newspapers.  I can not say enough good things about this man and his wife.  He made a positive difference in the world, and surely that is the best we can hope for.

Meanwhile, this will be no February 1985 blizzard but it will be a very intense & interesting ( dare I say ) storm to follow through coming days.

Have a great Monday.

p.s.

My dense fog ALERT for Middle Elevations appears to have been right on target.  Please slow down and take it easy my friends!

My Forecast For Today ( February 21 )

ALERT For Areas of Dense Fog & Low Cloud Bases Along And Southwest Of The High Knob Massif & Tennessee Valley Divide Overnight Into Sunday On SW Flow

*As of 12:30 AM on February 21 dense fog was widespread at elevations above 2800-2900 feet ( but will be locally lower in favored upslope locations on gusty SW winds ).

Dense fog ( orographic clouds ) has formed on SW Upslope Flow tonight and will be most favored for locations along & southwest of the High Knob Massif and Tennessee Valley Divide into Sunday as rainfall develops ( e.g., from the Wise area southwest along the U.S. 23 corridor toward Big Stone Gap where funneling of SW air flow tends to lower bases into Little Stone Mountain Gap and the Powell Valley Overlook section.  Caution is Advised for travelers ).

Thunderstorms Will Be Possible Today, Embedded In The Rain Shield.  Caution Is Advised For Lightning.

 Strong Rises Will Be Possible On Steep Creeks That Drain The High Knob Massif, Where Snow Melt Has Stream Levels Above Average At The Current Time.

ALERT For Dense Fog Formation From Late Sunday Night Into Monday At Middle-Upper Elevations Along And North Of The High Knob Massif-Tennessee Valley Divide On NNW-NE Upslope Flow

While any location could have fog after rain develops Sunday, the above ALERT is for widespread drops in cloud bases with northerly upslope flow behind a cold front late Sunday Night into Monday.  

Very dense fog is expected to develop along and northward of the High Knob Massif and Tennessee Valley Divide toward Midnight into the overnight-sunrise period of Monday.

Overnight Into Sunday Morning

Low clouds.  Areas of dense fog & drizzle.  A chance of light rain developing.  SW winds 5-15 mph, with higher gusts, on mountain ridges-plateaus below 2700 feet.  SW winds 10-20 mph, with higher gusts, along upper elevation mountain ridges.  Temperatures varying from the middle 40s to the lower 50s ( coolest at higher elevations and in sheltered valleys with light winds ).  Wind chills in the 40s, except some 30s at highest elevations in gusts.

This Morning Through This Afternoon

Rain.  A chance for thunder.  Locally heavy rain possible.  Rain becoming showery in nature late.  SW-WSW winds at 10-20 mph, with higher gusts, along mid-upper elevation mountain ridges & plateaus.  Areas of fog.  Temperatures varying from the upper 40s to upper 50s.

Tonight Into Monday Morning

Rain & showers tapering to drizzle.  W-WSW winds 5-15 mph, with higher gusts, shifting NNW-NNE.  Cloud bases dropping to obscure middle elevations in dense fog ( chance for freezing fog-drizzle at highest elevations amid the High Knob Massif by morning ).  Temperatures dropping into the lower 30s to lower-middle 40s by morning ( coldest at the highest elevations ).

A Major Winter Storm system will impact the mountain region during the February 24-26 period with strong winds, rain and a potential for significant NW Upslope Flow snowfall.  Stay tuned for updates on this developing storm system.

Reference my latest 022016 Extended Outlook for more details.

Weather Discussion ( February 20-21 )

An interesting setting was on display Saturday afternoon as widespread cloudiness along-south of the High Knob Massif was in contrast to partly sunny skies to the north.

Upslope flow across the still snow covered High Knob Massif allowed cloud bases to obscure upper elevations and form a very nice and persistent capping cloud mass.

Conditions inside the capping cloud mass featured dense fog and air temperatures in the mid-upper 40s.  Snow cover remained solid and deeper across northern slopes, with a little bare ground being visible along wind swept crest lines ( as on Eagle Knob below ).

Continuing melt of the previously 10″ to 20″ snowpack is keeping stream levels elevated, above average, on steep creeks draining the High Knob Massif tonight.

While forecast models predict the heaviest rain today to remain north of the area, along the surface low pressure track, any downpours ( especially if convective in nature ) could quickly raise these already elevated stream levels.

There will be potential for orographic enhancement on SW-WSW flow into the High Knob Massif area, as suggested by the NAM 4 KM Model along the Appalachians ( it tends to under-estimate enhancement in the High Knob Massif ).

The Bottom line – While no flood watches are officially in effect it will be wise for everyone living and driving along these already elevated steep creeks to monitor water levels today ( especially if rainfall becomes heavy with thunder ).

The focus by later tonight into Monday will be on a drop in cloud bases with upsloping northerly air flow that will be forced to rise upward from the Kentucky foothills into the High Knob Massif and Tennessee Valley Divide.

Depending upon how long the NW-NE air flow persists, low cloud bases & dense fog could be a factor for Wise and many other sites across Wise, Dickenson, and extreme northern Scott counties well into Monday ( worst case scenario being all day into the evening ).

Have a great Sunday.

My Weather Headlines ( February 20 )

Following 39 forecast days, with only 1 break day, I had to take a few days in between ACTION to catch up on some field work and get winter precipitation totals in order up to this point.

Refer to Winter Majesty In the High Knob Massif for details.

An ALERT for high winds was needed across our mid-upper elevations on Friday ( as I had figured ) with gusts of 30-50 mph being common.

These strong winds also made conditions feel cooler with 40s and 50s air temperatures ( not counting wind chills ) across middle-upper elevations above 2500 feet.

Looking ahead here are a few headlines ( I will be back forecasting daily beginning tonight or Sunday ).

*Rain will increase across the mountain area Sunday with a period of moderate-heavy rainfall possible.

*Air flow shifts to northerly upslope and an ALERT for dense fog may be needed by late Sunday into Monday at mid-upper elevations along and north of the High Knob Massif and Tennessee Valley Divide.  A period of freezing fog could even occur in upper elevations into Monday as conditions are damp & chilly.

*A Major Winter Storm system will impact the mountain region next week, with more significant snow likely ( as well as rain ).  Details are yet to be worked out regarding timing & precip amounts.

*This period is connected to a coming polar vortex split and another surge ( warm spike ) in temperatures over the North Pole during the next week to 10 days.  More arctic air surges are likely into the eastern USA in coming weeks as winter hangs on this year.

So enjoy these breaks!

My Forecast For Today ( February 17 )

ALERT For Freezing Fog At Middle-Upper Elevations Along & North of The High Knob Massif & Tennessee Valley Divide Overnight Into Wednesday Morning

Be cautious of slickness on decks-porches-steps and roadways at all locations where temperatures are freezing or below, and in the higher elevations, above 2500-3000 feet, where the most new snow accumulation occurred.  Please slow down and be careful.

Steep creeks draining the High Knob Massif have had strong rises, so caution is advised when around these creeks. The run-off has slowed with colder temperatures and reduction in snow melt.

Overnight Into Wednesday Morning

Low clouds with freezing fog at middle-upper elevations, especially along & northward of the High Knob Massif and Tennessee Valley Divide.  Light NW-N winds generally less than 10 mph.  Temps dropping into the 20s to lower 30s.

This Morning Through This Afternoon

Damp & chilly.  Low cloud bases lifting off of the middle elevations.  WNW-NW winds 5-10 mph, with higher gusts possible.  Chance of a localized PM shower of rain-mix in lower elevations and mix-snow at mid-higher elevations.  Temperatures varying from the mid 20s to mid-upper 30s, coldest at the highest elevations.

Freezing fog will likely continue at highest elevations during the day, with the potential for cloud bases to drop again into middle elevations ( below 3000 feet ) into Wednesday evening.

Tonight Into Thursday Morning

Low clouds ( cloud bases may drop back on mid elevations ).  Small chance of drizzle or flurries.  Light NW to N winds.  Temperatures widespread in the 20s ( dropping to around 20 degrees at the High Knob Massif summit level ).

An ALERT for strong SW winds may be needed by Friday as the pressure gradient increases along the Cumberland Mountains as warmer air is transported across the region.

Weather Discussion ( February 16-17 )

A wet snow fell across upper elevations, with mix in middle and lower elevations, during the early evening hours before a change to snow at all elevations by later Tuesday evening.

Abundant low-level moisture and light northerly winds have formed dense fog across middle to upper elevations, especially amid the favored lifting zone along and north of the High Knob Massif and Tennessee Valley Divide.

Tonight is again a perfect example to illustrate the temp error at Lonesome Pine Airport, with snow sticking to all above ground objects and other things while the reported air temperature was never below 34 degrees ( a 2 degree error, as I’ve noted many times in the past ).

Date and Time                             TEMP                  Dewpoint                                  Precipitation

Meanwhile, the U.S. Forest Service station reported 32 degrees from around ( or a little before ) the 10:00 PM observation thru Midnight ( with very dense fog it is now equal to the dewpoint ) and should drop slowly into the overnight.

This type of fog is enhanced by rising air on northerly upslope even though winds tonight are light.  It covers a very large area in Wise, northern Scott, and Dickenson counties but I can never seem to get that translated out beyond this area to officials responsible for issuing.

As air turns a little colder today we have a gloomy setting with abundant moisture in low-levels that will be hard to break up ( while some breaks can not be ruled out, models tend to increase afternoon-evening moisture enough to allow for at least a chance of a hit-miss shower of mix or drizzle at low elevations & snow at mid-upper elevations ).

The big picture does feature a relaxation in the recently harsh winter patter, but this will only be temporary, with cooling returning as soon as later Monday ( February 22 ).

The 00z February 17 run of the European 16 KM Model has again replicated a Miller A inland variant cyclone.  The good news this remains 6-7 days out and changes will occur.  The bad news will come if this type of storm is shown to verify!  Stay tuned.

By that time the main focus will likely be on potential for another significant winter storm as the large-scale pattern looks to again turn colder for a prolonged period heading into March ( this has been expected and is well predicted by past climatology of stratospheric warming events ).

I will issue a new Extended Outlook in coming days.

Make it a great Wednesday.

My Forecast For Today ( February 16 )

ALERT For Accumulating Snow Tonight – Beginning As Mix Below 2700 feet ( All Snow Above 2700 feet ) With A Fast Moving Clipper System

Steep creeks draining the High Knob Massif have had strong rises during today, so caution is advised when around these creeks. The run-off has begun to slow as air temperatures dropped back below freezing at higher elevations into the predawn-morning.

Overnight Into This Morning

Rain.  Heavy at times.  Rain changing to snow by the predawn ( especially along and west-northwest of the Cumberland Mountains ).  S-SSE winds 10-20 mph, with higher gusts, below 2700 ft.  SSE-SSW winds increasing to 15-25 mph, with higher gusts, on upper elevation mountain ridges.  Predawn winds shifting WNW-NW at 10-20 mph, with higher gusts.  Temperatures dropping during the predawn-morning back into the 20s to lower 30s.  Wind chills in the 10s and 20s along mid-upper elevation mountain ridges ( coldest at highest elevations ).

A period of moderate-heavy snow remains possible, especially in upper elevations where moderate snow has recently been falling on High Knob ( since 3:00 AM ), but trends have been for the most signficant snow band to remain just west and northwest of the Virginia-Kentucky stateline ( northwest of Pine Mountain ).

This Morning Through This Afternoon

Any early snow giving way to flurries, then mostly cloudy skies.  Winds becoming variable & light ( generally less than 10 mph ).  Temperatures varying from the upper 20s to the upper 30s ( coldest at highest elevations ).  Milder in lower elevations toward the Tri-Cities.

Tonight Into Wednesday Morning

Cloudy with snow developing.  A possible mix in lower elevations ( below 2700 feet ) at the beginning.  A period of moderate to heavy snow possible.  Winds NW-N 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges.  Temperatures dropping into the 20s to lower 30s.  Wind chills in the 10s & 20s on exposed mountain ridges.

Snowfall Forecast – Tonight Into Wednesday AM

General 1″ or less north of a Cumberland to Wise Line

1″ to 2″ below 3000 feet in Norton-Wise area

2″ to 3″+ above 3000 feet in High Knob Massif

Target Snowfall of 1.2″ in Norton-Wise ( +/- ) 0.5″ .  This implies potential for 0.7″ to 1.7″ of snowfall.  In general, lesser amounts of 1″ or less will be toward Pound-Clintwood with heavier amounts to the south toward the High Knob Massif.  The centroid of the clipper is tracking to the south, with heaviest amounts likely along the TN and NC border area from the Smokies northeast.  Any south shift in the current forecast track could bring the 1″ or less line farther south into Wise County.  Although this is expected to be a light event, a period of moderate-heavy snow remains possible and sticking on roadways ( especially with freezing of any initial mixture or drizzle ) will become most likely later tonight.

Weather Discussion ( February 16 )

I have cleaned up the forecast page this afternoon for the next clipper system that races through tonight.  Snow has been falling atop the High Knob Massif since about 3 PM.

Orographic clouds have obscured the High Knob Massif during late afternoon, with light snow falling.  What falls will be all snow at elevations above 2500 to 3000 feet, with a center point of 2700 feet for the initial rain-snow line.  A mix will be possible below this elevation until evaporative cooling allows for mostly snow at all elevations along and north of the High Knob Massif.

*Lower elevations south of the High Knob Massif in the Clinch, Powell, and Holston river valleys may be a little slower to see transition to all snow.

Roads remain covered and snow depths more than 6″ in the crest zone of the High Knob Massif this afternoon, but a big snow depth decrease of up to 8″ or so occurred with 2.00″+ of total precipitation during the past 24+ hours.

Steep creeks draining the high country began to respond by this morning, with strong rises, but also with a delay as the snowpack did act to absorb and release water more slowly.

My Forecast For Today ( February 16 )

ALERT For Heavy Rain Changing To Wet Snow By The Predawn-Morning Hours Of Today – Remain Alert For Water Ponding Along Roads, Snow Clogged Drains And In Low-Lying Poor Drainage Locations.

Caution For Black Ice and Snow On Roadways As Temps Drop Back To Around And Below Freezing

The highest risk region on the above graphic is along and northwest of the BLUE Line, which I have along Pine Mountain, with a high-moderate risk for locations along and northwest of the RED Line for at least a period of rain to wet snow.

A change from rain to wet snow is expected during the period between 1:00 AM and 4:00 AM, with changes first toward the southwest and at highest elevations rapidly overspreading the Cumberland Mountains.

Reference my 021516 Forecast and Discussion for more details.

Highest resolution models available are giving out a signal that fits the climatology of past such cases.  So I have posted the region where a risk of heavy wet snow will be greatest above.  THIS DOES NOT MEAN IT WILL OCCUR in a manner that is disruptive, but gives everyone an advance warning that it will be possible ( the risk for a change to heavy snow is high, with accumulations for any given place being the main unknown factor ).

The general trend is for heaviest snow amounts to the west and northwest, with lesser amounts toward the south and southeast, with respect to the Cumberland Mountains ( e.g., eastern Kentucky has a higher chance for more significant accumulations than does most of northeastern Tennessee, as illustrated by the models ).

When the 32 degree air moves back overhead there will be little lag time before it can begin to accumulate at lower elevations on the Virginia side of the stateline.  In between, a milder zone in the middle elevations ( like at Wise ) will have to be overcome ( air is colder both below and above the elevation of Wise tonight ). 

The temp at 1:00 AM is holding steady at 32 degrees in Clintwood, with a borderline rain-freezing rain event.

Overnight Into This Morning

Rain.  Heavy at times.  Rain changing to snow by the predawn ( especially along and west-northwest of the Cumberland Mountains ).  S-SSE winds 10-20 mph, with higher gusts, below 2700 ft.  SSE-SSW winds increasing to 15-25 mph, with higher gusts, on upper elevation mountain ridges.  Predawn winds shifting WNW-NW at 10-20 mph, with higher gusts.  Temperatures dropping during the predawn-morning back into the 20s to lower 30s.  Wind chills in the 10s and 20s along mid-upper elevation mountain ridges ( coldest at highest elevations ).

A period of moderate-heavy snow remains possible, especially in upper elevations where moderate snow has recently been falling on High Knob ( since 3:00 AM ), but trends have been for the most signficant snow band to remain just west and northwest of the Virginia-Kentucky stateline ( northwest of Pine Mountain ).

This Morning Through This Afternoon

Any early snow giving way to flurries, then mostly cloudy skies.  Winds becoming variable & light ( generally less than 10 mph ).  Temperatures varying from the upper 20s to the upper 30s ( coldest at highest elevations ).  Milder in lower elevations toward the Tri-Cities.

Tonight Into Wednesday Morning

Cloudy with snow showers developing.  A period of moderate to heavy snow possible.  Winds NW-N 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges.  Temperatures dropping into the 20s to lower 30s.  Wind chills in the 10s & 20s along exposed mountain ridges.

A new disturbance will renew snow showers tonight, with light to perhaps moderate  accumulations ( in favored upslope locations ) expected into Wednesday morning, especially for locations along and north of the High Knob Massif and Tennessee Valley Divide.

Weather Discussion ( February 15-16 )

I heard a friend of mine call this the Valentine’s Slop Storm, and that is likely as good of name as any for what has been a royal pain to deal with both underfoot and forecasting.

As of 2:00 AM, trends continued toward a change to wet snow but with the most significant accumulations more likely along and west to northwest of Pine Mountain, so that is where I have placed the highest risk for up to 4″ or more of snow.  It will be interesting to see how it plays out.

This has been a border-line freezing rain event throughout the mountain hollows of Dickenson County, and colder hollows in Wise County, with official temperatures in Clintwood holding steady at 32 degrees ( around 33 degrees in Birchleaf ).

Go up more than 1,000 vertical feet higher in elevation and temperatures have been in the 40s, even with the 2 degree or so warm bias at Lonesome Pine Airport, readings have been around 10 degrees or more warmer than adjacent mountain hollows.

Continue upward 1347 vertical feet above Wise and temperatures on Black Mountain have now dropped below freezing again after holding steady in the upper 30s for a good while.

Up on the High Knob Massif an initial transition from rain to freezing rain had turned to snow around 3:00 AM with a temperature of 29 degrees ( moderate to heavy snow was falling by 3:30 AM ).

Well over 2.00″ of total precipitation had fallen, as of 2:15 AM on Tuesday, at Big Cherry Lake Dam but had not yet ( at least ) generated a strong rise on adjacent Big Stony Creek.  This indicated that the deep snowpack has been absorbing and holding much of the rainfall ( with major shrinkage of the snow depth within orographic clouds and rainfall ).

Another round of snow develops tonight into early Wednesday with a clipper-like system.

Have a great Tuesday.

My Forecast For Today ( February 15 )

A Major Winter Storm Will Impact The Mountain Area With Multiple Threats Through Today Into Tuesday.  A Second Disturbance Will Then Renew The Chance For Significant Snow Late Tuesday Into Tuesday Night.

Let’s Try To Lay Out What Is Upcoming In Headlines:

Bands of moderate to heavy snow will give way to mixed precipitation into Monday AM to mid-day.

*Timing on the change from snow to mix-rain varies from the predawn to between sunrise and early afternoon.  This will be important to snow amounts, as a new wave of moisture over western-middle Tennessee & Kentucky moves into the area.

A change to all rain will become possible, with the potential for moderate-heavy rainfall  by later today.

*The potential for freezing rain will exist in any locations that remain below freezing ( of course ), and could even occur on surfaces which are very cold from 5+ days of sub-freezing conditions where air temperatures go above freezing.

*Other concerns that will need to be monitored include rainfall amounts and absorption by snow on roof-tops where significant weight could be added into tonight and Tuesday.  In addition, if rainfall becomes heavy, run-off issues could arise and this will need to be closely followed later today into tonight for poor drainage locations, roadways, and for rises on streams. 

A change back to snow, especially at middle to upper elevations above 2000 feet, will become possible by Tuesday Morning.  A period of heavy, wet snow will be possible during the morning, with greatest amounts expected at the highest elevations ( more than 3″ ).

*A surface low pressure will be intensifying along the eastern side of the Appalachians late tonight into Tuesday morning.  Models are not yet together on exactly how this plays out, but potential for a change to heavy, wet snow must be respected…especially from the Cumberland Mountains westward and northeastward.

It should be noted that the NAM Model is showing the type of development that is climatologically favorable for heavy snow in the Cumberland Mountains.  This has to be updated and followed very closely on new runs in coming hours.

A second system dropping into the mountain region will renew a threat for significant snow late Tuesday into Wednesday.

*If the above were not already enough, a second clipper system is forecast by models to race southeast into the base of this eastern USA upper air trough to renew the threat for a period of moderate to heavy snow late Tuesday into Tuesday night-Wednesday.

Overnight Into This Morning

Snow & blowing snow.  Heavy at times.  Possibly becoming mixed with sleet or freezing rain. SSE winds 5-15 mph, with higher gusts, on mid elevation mountain ridges-plateaus.  SSW-SW winds 15-25 mph, with higher gusts, along upper elevation mountain ridges.  Temps rising and becoming widespread in the 20s.  Wind chills in the 10s & 20s on exposed mid-upper elevation ridges & plateaus ( single digits in gusts along mid-upper elevation ridges ).

This Morning Through This Afternoon

Snow changing to rain ( possibly freezing in some places and upon very cold surfaces ).  SSE winds 5-15 mph, with higher gusts, on mid elevation mountain ridges-plateaus.  SSW-SW winds 15-25 mph, with higher gusts, along upper elevation mountain ridges.  Temperatures struggling to rise above freezing, especially over snow in valleys & along the highest windward ridges in the High Knob Massif ( mildest along exposed middle elevation ridges & plateaus ).

The forecast for tonight has been updated to include the increase in wind speeds shown by models.  Stay tuned for possible additional updates later tonight regarding snow potential for the predawn-sunrise period on Tuesday.

Tonight Into Tuesday Morning

Rain.  Heavy at times.  Rain may change to heavy, wet snow by morning ( especially mid-upper elevations ).  SSE winds increasing to 10-20 mph, with higher gusts, below 2700 ft.  SSE-SSW winds increasing to 20-35 mph, with gusts 40-50+ mph along upper elevation mountain ridges this evening.  Wind shifting WNW-NW in the predawn at 10-20 mph, with higher gusts.  Temperatures rising in the evening with 30s to lower 40s, then dropping during the predawn-morning back into the 20s to lower 30s.  New snow accumulations of 1″ to 3″ below 3000 feet, with 3″ or more above 3000 feet, along and north to northwest of Cumberland Mountains.

Many valleys outside of the mountain wave breaking zone will have much lighter winds.  Some could, in fact, remain under the current inversion which has dense fog and chilly temperatures over the snowpack.

At 7:45 PM the current official NWS temperature is 32.0 degrees in Clintwood.  Cold air has settled below an inversion layer through mountain valleys of this area, with fog and very light winds.

Weather Discussion ( February 14-15 )

My Afternoon Update

A break in the action this afternoon lets me see where we are at up to this point in the winter storm.  Yes, this point, there is much more to come ( especially for some ).

Observe the nice orographic wave clouds above the High Knob Massif this afternoon, with the summit level ( and back side in general in northern Scott County ) engulfed in the clouds.

At 2:00 PM a report from Joe & Darlene Fields finds 10″ of snow on the ground, with 6.0″ of new snow, at their home  in the High Chaparral community ( 3300 feet elevation ).

Around 7.5″ of new snow has fallen up at the summit level, with well over a foot of snow depth ( 12-18″ looks common ).  It has been a struggle to break above freezing.

Down below, in the City of Norton, snowfall was atypically less than often reported ( but well fits past climatology ), with Scott Craft & Caleb Ramsey measuring 3.7″ of new snow to 9:00 AM this morning ( 8″ of total snow depth ).

City of Norton Water Plant: 3.7″ new snow ( 0.43″ water content ) with 8″ of mean snow depth at 9:00 AM on February 15, 2016.

Up to 3:30 PM the PM MAX temperature had been 35.6 degrees at the City of Norton Water Plant.

In this case the 925-850 MB wind field was SSE-SSW across the High Knob Massif, with enhanced sinking air downward into the City of Norton.  Locations on the Scott County side of the massif have reported more, at lower elevations, than higher valleys on the Wise County side since low-level air was rising upward toward the massif from the SSE.  This helped enhance snowfall from Nickelsville to The Pines & Fort Blackmore of the Clinch River Valley.

Anna Hess reports 4.2″ of snow in The Pines area of the Clinch River Valley.

*The above setting being directly opposite to what occurs during NW Flow settings when enhanced snowfall is common in Norton with very little ( typically ) in the Clinch River Valley corridor.

Up to 10:00 AM today, my friend Chris Allgyer measured a total of 4.3″ of snowfall in Big Stone Gap.  While this was a “good” amount of snow for Big Stone Gap verses many NW and especially easterly ( when they truly get robbed ) flow settings, it was still significantly less than measured farther southwest along the Powell River Valley.

*Southwest of a Big Stone Gap to Pennington Gap corridor a SSE low-level flow undergoes much less sinking into the Powell River Valley as the southwestern flank of the High Knob Landform gets narrow and much lower in elevation ( i.e., Powell Mountain and Newman Ridge, with the interior Wallen Ridge also possessing a break southeast of The Cedars in Lee County ).

My friend Rodney Parsons measured 3.0″ of snow depth during Sunday up to the evening break.  He swept that off and by 10:00 AM Monday had 5″ new to bring the storm event tally to 8.0″ at his location near St. Charles.

Up to the north, in Clintwood, a total of 4.7″ of new snow has been measured so far during this event ( 6″ of depth ).  As of 4:50 PM the temperature in Clintwood is 34 degrees, down from a PM MAX of 36 degrees.  It is very foggy.

Wayne & Genevie Riner measured 5.8″ of snow up through their morning observation on Long Ridge of Sandy Ridge

Focus now shifts to what is next, with moderate-heavy rain expected tonight.  This will raise numerous concerns as the headlines at the top note.

Mainly adding weight to many roof-tops now having 4-8″ or more of depth, and the aspect of run-off into snow clogged drains, ditches, and roads where there could be enhanced ponding.  A flood watch is in effect through tonight.

In addition, models have increased wind speeds with very strong winds expected in upper elevations of the High Knob Massif and in mountain wave breaking zone amid localized places from Powell Valley in Wise County to Clinch Valley in Russell & Tazewell counties.  Wind gusts could top 50 mph in these places tonight.

There will be a transition to heavy, wet snow on the backside of the storm rain shield tonight into Tuesday morning.  This will begin in central Kentucky and wrap back into the Cumberland Mountains by morning.

The NAM Model has the snow band farther west, the GFS Model farther east, with the main idea being that rain will change to heavy, wet snow for a period of time along back of the rain shield into Tuesday morning.  This will need to be closely followed and updated again later tonight.

The best chance for significant snow on Tuesday Morning will be along and northwest to northeast of the Cumberland Mountains.

My Overnight Discussion

Reference my 021416 Forecast discussion for more details.

The most complex weather system of the 2015-16 winter season is making it hard on forecasters and models alike with large-scale rising motion over retreating arctic air.

Instead of coming together as one consolidated storm, this system is in open wave form with embedded disturbances that may finally congeal enough by late today to develop a more distinct area of low pressure ( as another upstream piece of energy dives southeast to continue the mayhem ).

The track of a developing surface low on the NAM Model, as well as the new European 16 KM Model, is one favoring the development of significant snow in the local mountains.

Should this occur, the window for purely rain will close rapidly as rain changes back to snow ( of course, assuming snow falling now makes the predicted transition to mix-rain into today, which all models currently agree upon ).  Whether all temperatures at the surface can rise above freezing is another story, that only time will determine.

Surface temperatures over snow are always problematic, with tendency toward inversion formation.  Only if strong winds aloft, and along the high mountain crest lines, can mix downward with vigor can most all surface temperatures rise above freezing.

The NAM Model predicts the entire area to be well above freezing by 1:00 PM today, with a CAD ( cold air damming ) wedge of low-level cold air hanging along eastern slopes of the mountains chain ( with warmer air aloft above that ).  Typically, with extensive snow cover, it is often not that clear cut and simple in this complex terrain.  Time will tell.

Temperatures over snow, with strong upsloping, into highest elevations of the High Knob Massif have also always been very problematic in these settings ( i.e., a struggle to get above 32 ).

The wave diving into the backside of this system looks rather impressive on the NAM Model, with strong upper diffluence ( divergence aloft ) and vorticity advection by late Tuesday into Tuesday night.  The European Model is a little slower than the NAM in digging this into the area.

The GFS Model has beat the NAM Model up to this point in the storm with respect to total snowfall.  It predicts that snowfall at the Wise gridpoint will increase by 4.9″ from this morning into early Thursday ( bulk coming during the Monday Night-Tuesday Morning transition back to snow ).  This is, of course, just a single model’s prediction.

One thing seems certain, an axis of heavy precipitation will develop by late today into tonight such that either way ( be it heavy rain or heavy rain to more heavy snow ) it will not be pleasant.  Stay tuned for updates later today.

It should be noted that the snowfall pattern during this event has been dominated by meso-scale snow bands, with indications of gravity waves ( linear features inside them ) as very strong winds aloft interact with the mountains and jet streams ( jet streaks ) aloft.

While I did not take time to draw a new snowfall map, my previous map holds as most places will be coming in amid upper portions of the ranges ( especially if more snow falls late tonight-Tuesday ).

Please try not to travel overnight into this morning if possible, giving VDOT time to work and temperatures time to rise from current levels well below freezing.