Mountain Area Forecast ( Dec 31-Jan 3 )

ALERT For Bitterly Cold Air To Continue Through New Year’s Day Into Tuesday

Air temperatures will remain below 20 degrees at middle-lower elevations, and below 10 degrees at upper elevations, along and north of the High Knob Massif-Tennessee Valley Divide, into Tuesday.  Wind chills will make conditions feel much colder at times, especially at middle-upper elevations.

While New Year’s morning ( Monday ) will tend to be coldest at highest elevations, on peaks, both Tuesday & Wednesday mornings will tend to be coldest in mountain valleys.

Extreme Caution Is Advised To Protect Against Frostbite & Hypothermia For All Warm-Blooded Creatures Which Have To Balance A Heat Budget

New Year Eve Into New Year Morning

Partly to mostly cloudy.  A chance of flurries and snow showers overnight into morning.  Bitter.  NNW-NNE winds 5-10 mph with higher gusts along middle-upper elevation mountain ridges-exposed plateaus.  Temperatures varying from -5 below zero to 8 degrees.  Wind chills 5 above to -10 below zero at elevations below 2700 feet, with chill factors of -5 to -15 below zero at elevations above 2700 feet ( as cold as -20 to -25 degrees below zero on highest peaks ).  Rime formation possible again at highest elevations.

Afternoon Of New Year’s Day

Mostly cloudy with flurries and snow showers continuing.  Bitter.  NW winds 5 to 10 mph with higher gusts.  Temps varying from single digits in upper elevations to 10s at middle-lower elevations in locations along-north of the High Knob Massif and Tennessee Valley Divide ( a little “warmer” south into river valleys of the Clinch, Powell, Holston ).  Wind chills in single digits above & below zero, except -10+ below zero in gusts highest elevations.

Monday Night Into Tuesday Morning

Becoming mostly clear.  Chance of evening flurries.  Bitter.  NW-NNW winds 5-10 mph, with higher gusts, mid-upper elevation mountain ridges.  Light valley winds.  Temps varying from  5 above zero -5 below zero, except locally as cold as -10 F below in upper elevation mountain valleys.  Wind chills between 0 degrees and -25 below zero along exposed mountain ridges ( coldest at upper elevations ).

Tuesday Afternoon

Mostly sunny.  Bitter.  Light NW winds.  Temperatures varying from the 10s to lower 20s ( mid 20s possible in exposed middle elevation locations with a low-level inversion being possible to keep some valleys colder ).

Tuesday Night Into Wednesday Morning

Clear through the evening.  Increasing high clouds overnight into morning.  Light winds becoming SW along mid-upper elevation mountain ridges.  Rapid evening temp drop in mountain valleys.  Temperatures varying from 10s along mountain ridges to single digits in valleys, except below zero in colder valleys at upper elevations.

The chance for more significant snowfall is being monitored with development of NW upslope flow behind major cyclogenesis in the western Atlantic by January 4-5 in combination with a reinforcing surge of bitterly cold air.  Stay tuned for updates.

Weather Discussion ( Bitter Cold )

New Year Day Update

My update is to continue mostly cloudy skies with flurries and snow showers this afternoon as low-level moisture has been greater than models resolved amid this bitter air.

Flurries and snow showers redeveloped in the overnight and morning hours of New Year’s Day, as I had forecast, and are continuing at upper elevations in the lifting zone of the High Knob Massif and across upslope locales this afternoon.

The air temperature was just 2 degrees, with well below zero wind chills, on Eagle Knob at the time of the above view when a peep of sunshine helped to illuminate the flakes.

Temperatures had warmed to a relatively “balmy”, by comparison, 15 degrees in Clintwood at 3:30 PM, with readings having climbed to about 10 degrees at Nora 4 SSE ( below ).

An interesting local feature that I picked out was a plume generated by cold air flowing down South Holston Lake on NNE flow during the morning.

This NASA pre-sunrise image, which is essentially infrared, was able to detect ( as it often does ) the warmer surfaces of the largest TVA Lakes in northeastern Tennessee which show up as a darker hue amid more light colors.  Upslope clouds, the edge of which I denoted by a red line, could also be seen distinctly.

In this case the air flow trajectory was just right to align with the long-fetch of South Holston from the stateline south to south-southwest.

The image below is without any labels and shows the plume well as of 9:00 AM on New Year’s Day, with upslope clouds banked against the High Knob Massif-Tennessee Valley Divide & Clinch Mountain toward the north.

Many interesting features could be seen on the daily Modis Terra Satellite pass, but the South Holston Lake cloud plume was not distinct or had dissipated with a change in the wind trajectory that helped form it this morning.

One reason this has been the coldest New Year’s Day on record ( 19 degrees in 1977 was the former record in Wise; although, to be accurate that was likely due to a carry-over from the 5:00 PM observation time on December 31 and will need to be checked given the former 5 PM daily obs time ) is that snow cover is now widespread between the Ohio River and Canada to allow bitter air to flood south unmodified.

Previous Discussion

A light coating of snow, thin glaze of ice, and riming on trees at upper elevations, greeted the final day of 2017.

A general 0.2″ to 0.8″ of accumulation occurred across the area with the freezing drizzle-frozen cloud droplets changing over to all snowflakes overnight into Sunday morning.  The messy mix being regenerated far to the south with a minor shortwave into Sunday afternoon, between the Tri-Cities & Asheville, which have been south of the most bitter air ( note the very tight temperature gradient observed at 7 AM Sunday morning below ).

Sunday afternoon temperatures reflected this pattern, with variations from single digits in the High Knob Massif to the 20s in the Great Valley ( Abingdon through the Tri-Cities ).

With a southern Appalachian snow drought again running this winter, bitter COLD was the dominant feature despite some roads being slick.  Once NW flow cloud bases finally lifted a winter wonderland of beauty was displayed for miles and miles across the high country of the massif.

The main problem being it was just about too cold to enjoy it with air temperatures in the single digits and wind chills below zero throughout the day.  A simple break-down or problem could be extremely dangerous in such conditions, as residents living at elevations above 3000 feet know very well.

Another increase in low-level moisture with arrival of the 850 MB thermal min will help regenerate snow showers and flurries into New Year’s morning, especially along the upslope side of the mountains on northerly air flow.

Although orographic forcing has been weak, and moisture very limited, if nothing else is learned about true arctic air it is that little is required to generate snowflakes-precipitation.  Any low level cloud crossing the High Knob Massif in such bitter air can generate flakes of snow, especially if there is a connection to the Great Lakes.  Upper elevations in the massif have not averaged 75″ to 100″+ of snow per winter season, during recent decades, without this being part of the snowfall regime.

Locations south of 38 degrees North latitude have been in a snow drought along the Appalachian chain due in part to a notable lack of Great Lake moisture transport, especially in favored lifting zones along the western side of the range.

Formation of deep low pressure in the western Atlantic will therefore be important to monitor, since it offers a chance to draw Great Lake moisture south with enough gradient present to produce a mountain torque = upslope snow.

*A much more efficient result would be if the storm were farther west than shown above, to generate better forcing on a cyclonic flow field; however, for snow lovers in a drought any hope for snowfall is better than none. 

Mountain Area Forecast ( Dec 29-Jan 1 )

ALERT For Slick-Icy Conditions Saturday Evening Into The Overnight In Locations Along And North Of The High Knob Massif-Tennessee Valley Divide In Wise, Dickenson & Buchanan Counties

A sleety mix of drizzle, frozen water droplets, and snow is coating secondary roads, cars, sidewalks etc..in Dickenson County, with showers of mostly snow appearing to be more common at highest elevations where temps are in the 10s.

*As of 6:30 PM it is now difficult to even stand up on sidewalks or exposed decks in Clintwood.  CAUTION IS Advised to prevent falls!

As temps continue to drop more dendrites will likely develop at lower elevations, with a burst or two of heavier snow being possible as the Arctic Front crosses the western front range of the mountains Saturday night ( Dec 30 ).

*The orographic clouds producing this precipitation is being overshot by Doppler radar beams, so little is showing up.

The Coldest Air Mass Of The Season Is Expected To Arrive During New Year’s Weekend

A large mass of bitterly cold air is expected to pour south into the mountains during New Year’s Weekend.  While some snow will be likely with northerly upslope flow, amounts continue to look light with a dusting up to 1″ generally being possible ( up to 2″ at upper elevations in the High Knob Massif ).

This will be the beginning of a prolonged period of bitterly cold conditions that may eventually allow for a more important winter storm to impact the Appalachians in the first week of January.

Friday Night Into Saturday Morning

Mostly cloudy.  A chance of snow flurries.  Winds SSW-W at 5-15 mph, with higher gusts ( especially overnight into early morning when gusts over 30 mph will become possible at highest elevations ).  Temps varying from the upper 10s to upper 20s.  Wind chills in the 10s to lower 20s, with single digits at highest elevations toward morning.

Saturday Morning Through The Afternoon

Mostly cloudy.  A chance of snow showers & flurries.  Cold.  Winds W-WNW at 5-15 mph with higher gusts.  Temps near steady or slowly falling in the 20s middle-lower elevations and the 10s at highest elevations.  Wind chills in the 10s to lower 20s, with single digits to near 0 degrees at highest elevations ( especially in frequent gusts ).  Milder south of the High Knob Massif-Tennessee Valley Divide into river valleys of the Clinch, Powell, Holston.

Saturday Night Into Sunday Morning

Turning colder.  Chance of snow showers and flurries.  A burst of evening snow possible, especially along and north of the High Knob Massif & Tennessee Valley Divide.  Winds shifting NNW-NNE at 5-15 mph, with higher gusts.  Temps dropping into the single digits to low-mid 10s.  Wind chills dropping into single digits above and below zero, except to around -10 below zero in gusts at highest elevations.

Sunday Morning Through Sunday Afternoon

Mostly cloudy.  Chance of flurries.  Bitterly cold.  N-NNE winds 5-10 mph with some higher gusts.  Temperatures near steady in the single digits at upper elevations to the mid-upper 10s at lower-middle elevations along-north of the Tennessee Valley Divide and High Knob Massif.  Wind chills in the single digits above and below zero.

New Year Eve Into New Year Morning

Partly to mostly clear.  Bitter.  N-NE winds 5-10 mph with some higher gusts along mid-upper elevation mountain ridges-exposed plateaus.  Temperatures 0 to 10 degrees.  Wind chills 5 above to -5 below zero below 2700 feet, with chill factors of -5 to -15 below zero at elevations above 2700 feet ( as cold as -20 degrees below zero on highest peaks ).

Reference my 122217 Forecast & 122617 Forecast for recent information and a look back at a white Christmas Holiday.

Weather Discussion ( Bitter Cold )

Late Saturday Afternoon Update

Due to shallow low-level moisture that is being lifted along the upslope side of the mountains, conditions have become quite icy with a nasty mix of drizzle-sleet-snow freezing on contact in the Clintwood area ( to note only one place ).

Some vertical cloud development was showing up along the 850 MB arctic front late Saturday, with this nasty mix over the mountains falling south of this boundary.

The 850 MB arctic front and thermal min are important features, especially in the mountains when interacting with complex terrain.  It is hoped that more snow and less drizzle will develop as the vertical temp profile turns bitter upon passage of this boundary ( which will be denoted by a shift to more northerly winds and onset of a temp plunge ).

Previous Discussion

A little snow remains on the ground around Norton-Wise, with extensive snow cover; albeit light versus normal, in the high country of the High Knob Massif.

Friday temperatures peaked at 33.8 degrees in Clintwood and around freezing or below at the elevations of Norton-Wise and Sandy Ridge ( LNP possessing a 1 degree Celsius warm bias ).

It is hoped that you enjoyed this Friday’s “warmth” as temperatures are going to turn much colder during the weekend as bitter arctic air tightens its grip.

The source region for the incoming bitter blast could be seen this morning on the European Model analysis of 850 MB temperature anomalies across North America ( above ).

While COLD will be the main story, there should be just enough moisture and lift to generate some snow showers and flurries along the upslope side of the mountains with Great Lake moisture trying to make it south following a wind shift to the north behind a passing clipper system.

With such bitter air it takes very little moisture to generate snowflakes, as observed most recently on December 27, when combined with low-level rising air.  Snow densities will not be even close to 10:1, as models use.

Bitter cold is the main aspect of concern, with MAX temps likely to remain under 20 degrees for much of the mountain area during Sunday-Monday.  Please be careful and take care of yourself, elderly and pets.

Residents who live in the high country, or those who may be planning to hunt, hike, or do other outdoor activities, should realize that temperatures during December 31-January 1 will generally remain in the single digits by day at elevations above 3000 to 3500 feet, with well below zero wind chills.

Depending upon sky cover, winds, etc…some downward adjustment of low temperatures may be necessary during the weekend-early week period.

Mountain Area Forecast ( Dec 26-29 )

The Coldest Air Mass Of The Season Is Expected To Arrive During New Year’s Weekend

A large mass of bitterly cold air is expected to pour south into the mountains during New Year’s Weekend.  While some snow will be likely with northerly upslope flow, amounts continue to look light.

This will be the beginning of a prolonged period of bitterly cold conditions that may eventually allow for a more important winter storm to impact the Appalachians in the first week of January.

Former ALERTS

Air Will Turn Increasingly Bitter & Much Drier ( Arctic Dewpoints ) Later Wednesday Into Thursday Morning With Northerly Flow Behind A Passing Disturbance

The coldest temperatures of this winter season to date are expected Wednesday Night Into Thursday Morning as bone dry arctic air combines with light winds and mainly clear skies to allow temperatures to tank.

Morning lows into December 28 varied from below zero in colder valleys of the High Knob Massif to 5 degrees on Long Ridge of Sandy Ridge and 6 degrees in Clintwood.

Detailed Forecast

Tuesday Night Into Wednesday Morning

Mostly cloudy.  Cold.  Small chance of snow flurries.  Light northerly winds during the evening increasing to 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges overnight into morning.  Temperatures dropping into the low-mid 10s to the low-mid 20s ( coldest within upper elevations ).  Wind chills dropping into the single digits and 10s, locally below zero on peaks by morning.

Wednesday Afternoon

Becoming mostly clear into evening.  Colder.  Light snow or flurries possible prior to clearing.  NNW to NNE winds 5-10 mph with higher gusts.  Temps near steady or falling in the 10s upper elevations and 20s middle to lower elevations.  Wind chills in single digits and 10s, except below zero in gusts higher peaks.  Riming highest ridges.

Wednesday Night Into Thursday Morning

 Mostly clear & bitterly cold.  Light winds.  Temperatures dropping into the single digits to 10 degrees, except around 0 degrees or below zero in upper elevation valleys.

Thursday Afternoon

Increasing mid-high clouds.  Light winds becoming S-SW at 5 to 10 mph, with higher gusts on upper elevation mountain ridges.  Temperatures rising into the low-mid 20s to lower 30s ( coldest upper elevations ).  Wind chill factors in the 10s and 20s ( single digits to around 10 in gusts along high mountain crest lines ).

Thursday Night Into Friday Morning

Partly to mostly cloudy.  Light valley winds.  SW-W winds increasing to 10-20 mph, with higher gusts, along middle-upper elevation mountain ridges ( especially at elevations above 2700-3000 feet ).  Temperatures in the 10s to middle 20s.  Wind chills in single digits & 10s on higher ridges.

Friday Afternoon

Partly to mostly cloudy.  Cold.  Variable winds generally less than 10 mph.  Temperatures varying from 20s to lower 30s, coldest upper elevations.  Wind chills in the 10s & 20s.

Reference my 122217 Forecast page for a review of the Christmas Holiday period and The High Knob Landorm for more information.

Weather Discussion ( Arctic Air )

Thursday Afternoon ( Dec 28 ) Update

For a 4th consecutive day temps have remained below freezing in locations along-north of the High Knob Massif and Tennessee Valley Divide ( MAX 28 degrees Clintwood ).

For the 2nd consecutive winter a snow drought is ongoing, with totals so far this season ( October-December 2017 ) of around 12″ atop the High Knob Massif and 16″ on Snowshoe Mountain in West Virginia.  How often can it be said, at this point in a winter season, that places in Georgia have had more snow than these 4,000+ foot peaks which are among the most favored for heavy winter snowfall totals?

Although snow continues to cover the ground in the high country of the High Knob Massif, it is nothing like it often would be during this time of year with season-to-date snowfall being much less than it typically is just during December.

If it were not for the freak southern snow band of early December there would not have been hardly any snow this season atop the highest southern Appalachian peaks, where the summit of Mount Mitchell is currently snow-rime free with no white Christmas in 2017.

While Snowshoe Mountain will pick up some snow from clippers tracking through the northern stream flow into New Year’s weekend, the southern Appalachians will be mostly in between northern and southern jet waves.

A significant north-to-south temp gradient has and will continue to bias places at higher latitudes along the Appalachian chain for colder temperatures.  For example, morning MINS on December 28 reached 12 degrees on Mount Mitchell versus 1 degree Fahrenheit on High Knob and -7 below on Snowshoe Mountain.  Despite being significantly higher in elevation, the 6684 foot summit of Mitchell was standing amid much milder ( relative speaking ) 850-800 MB air compared to these lower summits at higher latitudes.  Far to the north, the 6288 foot peak of Mount Washington, NH recorded -34 degrees below zero ( -89 F below wind chill ) on December 28.

If a big east coat storm bombs next week then a blob of this truly bitter air could get pulled farther south to impact the southern Appalachians.  Stay tuned for updates.

As bitterly cold air settles south on northerly flow there will be the chance for some snow accumulation, especially along and north of the High Knob Massif-Tennessee Valley Divide where air will be orographically forced to rise.  It takes very little to generate snow in such cold air with vertical lifting, so this will bear watching – the only ingredient needed will be a little moisture!

Although timing has varied and run-to-run differences have been common, models continue to suggest a major storm will develop in this pattern with current timing  being after New Year’s by the middle of next week.

Regardless of snow, the next week to ten days are going to be bitterly cold with a MEAN 850 MB temp of -11 to -12 C being predicted by the ensemble mean of the European Model group above the High Knob Massif area.

This is likely to generate temperatures well below zero as time passes, with -20 below being a target number for the continued extirpation of Hemlock Wooly Adelgids.

*Hemlock Wooly Adelgids ( Adelges tsugae ) were killed out of the high country of the High Knob Massif during the 2014-15 winter season when air temperatures plunged into the -20 to -30 degrees below zero ( Fahrenheit ) range; however, because conditions did not get that cold to the south and southeast of the massif area the adelgids survived and subsequently migrated back into the massif area during the past couple of years.

While many Canadian Hemlock ( Tsugae canadensis ) trees have been killed since adelgids were able to breech the mountain range since the late 1990s, many are also looking good currently thanks in part to the bitter cold of February 2015.  Adelgids were found in eastern Virginia as long ago as the 1950s, but were never able to cross the Appalachians into this area due to periodic bitter cold spells during winter ( -20 F being their kill threshold ). 

Wednesday Afternoon Update

My update this afternoon includes slowing down the clearing a little, until late afternoon-early evening, and introduces light, fine snow-flurries in upslope locations.

Low clouds are banked up against western slopes of the mountains & adjacent foothills of the Appalachians with lingering moisture in advance of bone dry continental Polar air.  A little light snow and flurries are falling out in upslope locations.

Temperatures at 1:00 PM varied from 15 degrees ( wind chill 3 F ) on Eagle Knob of the High Knob Massif to 36 degrees down in the Tri-Cities of the Great Valley and 41 degrees in Wilkesboro, NC.

Temperatures at 3:00 PM varied from 13 degrees ( wind chill 0 F ) on Eagle Knob of the High Knob Massif to 38 degrees down in the Tri-Cities of the Great Valley and 43 degrees in Wilkesboro, NC.

Previous Discussion

Arctic air is the main weather feature to rule the mountain landscape through coming days, with a reinforcing short-turn push featuring a dewpoint front that will introduce continental Polar Air during Wednesday into Thursday.

Although temperatures remained below freezing throughout December 26, a good amount of snow “disappeared.”  How can snow vanish like this?  While some insolation penetrates clouds, especially thinner sections, the main factor with a dry air mass is sublimination, a process by which a solid changes into a vapor without going through the melting phase.  Even at the highest elevations this process can cause snow cover to decrease.

Sublimation is an endothermic process, which means it absorbs heat and thereby aids cooling of the air.  This is one reason that afternoon temperatures in locations that had Christmas snow only managed to reach the lower 20s ( high elevations in the High Knob Massif ) to lower 30s during Tuesday ( December 26 ).

The vertical air column will be drying significantly behind a passing disturbance-dewpoint front into Wednesday, which sets the stage for bitterly cold conditions to develop into the evening hours of Wednesday and Thursday morning.

Dewpoints to around -40 Celsius ( -40 F below zero ) are being predicted within the 900-850 MB level by Wednesday Night, such that the only aspect to hinder temperature drops will be any areas of middle-high altitude cloudiness.  This will help prevent the full cooling potential from being reached, but still produce bitterly cold temperatures.  High valleys, especially with lingering snow within the High Knob Massif, could easily drop to 0 degrees or below in a setting like this ( as even over bare ground many mountain valleys will drop into single digits unless extensive cloudiness develops into Thursday morning ).

The last time 0 degrees was recorded in high valleys of the High Knob Massif featured a similarly bone dry lower atmosphere into morning hours of March 16, 2017 ( above ).

Although a huge blast of bitterly cold air is looking likely by New Year’s weekend, details with respect to how that plays out are yet to be determined with models currently in a state of disarray handling shortwaves traveling through the longwave flow field.  So stay tuned. 

Mountain Area Forecast ( Dec 22-25 )

My Forecast & Alerts With Later Verification Images Added

Upcoming And Current Alerts

 A Sharp Temperature Drop Is Expected Christmas Eve Night Into Christmas Day With Widespread Flurries & Snow Showers Tonight Into Christmas Morning As Air Temperatures & Wind Chills Turn Bitterly Cold.  

Light Accumulations Will Be Likely, With Most Significant Amounts At Upper Elevations.

The odds of having enough snow for an “official” white Christmas will be greatest at upper elevations in the High Knob Massif, and generally higher in locations along and upstream of the massif and Tennessee Valley Divide ( including communities such as Clintwood, Wise, Norton, Big Laurel, Banner Mountain, Herald, Carrie, Maple Grove, Big Ridge, Caney Ridge, Hill Ridge and Long Ridge as only a few examples of many ) versus locations lying downstream in river valleys of the Clinch, Powell, and Holston.

Snowfall Forecast ( Christmas Eve-Morning )

1″ or less below 2000 feet

1-2″ from 2000 to 3000 feet

2-3″ above 3000 feet

*Little to no snow accumulation is expected in downslope locations of the Clinch, Powell, and Holston river valleys.  Greatest amounts are expected above 3000 feet in the High Knob Massif.

Superintendent Andrew Greear, of the City of Norton Water Plant, reported 1.5″ of morning snowfall ( 1-2″ on the ground ) at the base of the High Knob Massif ( elevation 2342 feet ).

Darlene & Joe Fields reported 2″ of Christmas Morning snow depth in the High Chaparral community of the High Knob Massif.

Reference my 54-Year Christmas History below for a review of many past Christmases that possessed a similar distribution, with northern slopes within the high country of the High Knob Massif possessing one of the greatest probabilities ( 64% ) of having at least 0.5″-1″ of snow on the ground on Christmas Morning along the entire expanse of the central-southern Appalachians. 

Reference History Of Christmases Past

Former Alerts

ALERT For Strong SSW-SW Winds From Midnight To Noon Saturday For Middle To Upper Elevations And Lower Elevations In The Pound-Clintwood Corridor

A couple waves of moderate-heavy rain will begin to impact the mountain region Friday afternoon.  A low-level jet, with strong winds will develop between the heaviest periods of rain by late Friday Night into Saturday Morning.  Wind gusts of 30-50+ mph will become possible across middle-upper elevations.  The lower terrain has been added due to downward momentum transfer.

This verified well with a low-level jet developing along the western slopes of the Appalachians.

Peak Reported Wind Gusts

49 MPH
*Lonesome Pine Airport

53 MPH
Black Mountain Mesonet

53 MPH
Flatwoods Mountain Mesonet

*Reported in between recorded AWOS observations.  Localized power outages were reported across the area.  No official NWS advisories were posted prior to this event.  This despite predicted formation of a SW flow jet ( not SE mountain wave jet ) along the western slopes of the southern Appalachians.  Emphasis on the strongest winds was placed on the wrong side of the mountain chain by forecasters, with a wind advisory being issued only following development of this high wind event ( speeds at the upper elevations would have justified a High Wind Warning ).  Numerous tree limbs, and some trees, were downed.

Miles and miles of roads looked like the above following the high wind event of December 23.  Residents had to cut a few larger trees which completely blocked several roadways.

*Any forecaster who reads statements like above are wrong if they assume these are criticisms.  One of the biggest obstacles to forward progress and learning is such erroneous assumptions, as only with a mutual respect can forecasting in complex terrain be advanced ( respect between researchers and forecasters ).  For myself, personally, forecasting is only a by-product of my core interest which is the climate system and its components.  This website and the High Knob Landform were started as a means to document conditions in complex terrain that had previously been undocumented.  If advancement of forecasting through learning is a byproduct then it will be only one of many that arises from the undergraduate research program at the University Of Virginia’s College At Wise.

Strong Rises On Creeks And Ponding Of Water In Low-Lying, Poor-Drainage Locations Will Become Possible Into Saturday

A second wave of moderate-heavy rain, with possible thunder, will impact the mountain region Saturday.  Accumulative amounts on already wet ground will set the stage for strong rises on streams, especially those draining the High Knob Massif-Black Mountain corridor where rainfall amounts will be enhanced by orographic forcing on moderate-strong upslope flow during Saturday.

A general 1.50″ to 2.50″ of rain fell in Virginia-Kentucky border counties ( 2.15″ in Clintwood to 4 PM December 23 ), with locally higher amounts within the High Knob Massif-Black Mountain corridor.

Dropping Cloud Bases With Dense Fog Formation Will Be A Concern For Mid-Upper Elevations Along & North Of The High Knob Massif-Tennessee Valley Divide By Saturday Night Into Sunday Morning On Development Of Northerly Upslope Flow.  Freezing Fog Will Become Likely In Upper Elevations.

High elevations in the High Knob high country, into Christmas Eve morning, were rime coated but clouds remained so dense that it was impossible to get photographs to show the extent beyond close-ups.

In the above view Hawthorn ( Crataegus spp. ) trees, which here are Pleistocene relicts, are coated by an icy, glassy-type of rime which underwent deposition at temperatures in the 28-32 degree range.

A wet low-level atmosphere will combine with cold air transport on developing northerly upslope flow to drop cloud bases across middle elevations between 7 PM Saturday and 10 AM Sunday, in locations along and north of the High Knob high country and the Tennessee Valley Divide.  Very low visibilities will impact the busy U.S. 23 corridor between Powell Valley and Pound Gap within Wise County, as well as all mid-upper elevation roads and communities from extreme northern Scott County across Wise County into Dickenson County and southern portions of Buchanan County.

Saturday evening ( December 23 ) cloud bases have been variable between 2500-3000 feet, and solid above 3000 feet, with sudden changes in visibility in the variable layer.  Temperatures are below freezing at highest elevations with freezing fog.  Drizzle has been falling at lower-middle elevations.

Caution is advised for travelers along the U.S. 23 corridor and on all higher elevation roadways into Christmas Eve morning.

Detailed Forecast Dec 22-25

Overnight Into Friday Morning

Mostly cloudy.  S-SW winds 10-20 mph, with higher gusts, on middle-upper elevation mountain ridges-plateaus.  Low clouds ( dense fog ) at highest elevations High Knob Massif and Black Mountain.  Temperatures varying from 30s in the colder, sheltered valleys to the mid-upper 40s.  Wind chills in the 30s & 40s ( coldest in upper elevations ).

Friday Morning Through The Afternoon

Mostly cloudy.  A chance of drizzle or scattered light rain showers into early afternoon, then rain becoming likely.  Low clouds, dense fog at high elevations in the High Knob Massif early, then areas of fog developing with rain across the area.  Winds SSE-SW at 10-20 mph, with higher gusts, along mountain ridges-plateaus.  Temperatures varying from 40s in upper elevations to the low-mid 50s.  Wind chill factors in the 30s at highest elevations.

Friday Night Into Saturday Morning

Rain or Periods of Rain.  Heavy at times. Windy at upper elevations, then becoming windy at middle elevations by morning.  Winds S-SSW at 5-15 mph increasing to 15-35 mph, with higher gusts, at elevations below 3000 feet.  Winds SSW-SW 15-25 mph and increasing to 25-35 mph, with higher gusts, on mountain ridges above 3000 feet.  Temps steady or slowing rising in the upper 40s to middle 50s.  Wind chills in the 30s at highest elevations.

Saturday Afternoon

Showers. Thunder possible.  Rain may be heavy at times.  Windy.  SSW-WSW winds 10-25 mph, with higher gusts. Temperatures in the 50s to near 60 degrees, dropping during mid-late afternoon.

Saturday Night Into Sunday Morning

A chance of showers to drizzle.  Turning colder.  Dropping cloud bases with dense fog development possible at mid to upper elevations along and north of the High Knob Massif and Tennessee Valley Divide.  Winds shifting NNW-NNE and diminishing to generally 10 mph or less.  Temps dropping into the 30s, varying from upper 20s to around 30 degrees at highest elevations to mid-upper 30s.

Sunday Afternoon

Cloudy.  Colder.  A chance of snow showers & flurries, especially at upper elevations ( mix possible mid-lower elevations ).  W-WNW winds 5-15 mph, with higher gusts.  Temperatures in the 30s to lower 40s ( coldest at highest elevations ).  Wind chills dropping into 10s & 20s at high elevations.

Christmas Eve Into Christmas Morning

Snow & snow showers during the evening, then a chance of snow showers and flurries.  A snow burst possible during the predawn.  Turning bitterly cold.  Windy.  WNW to NW winds 10-20 mph, with higher gusts.  Temps dropping into the 10s to around 20 degrees, except single digits at highest elevations.  Winds chills falling into the single digits to low 10s, except 0 to -15 below zero across upper elevations above 3000 feet.  Rime formation in upper elevations.

Snowfall Forecast ( Christmas Eve-Morning )

1″ or less below 2000 feet

1-2″ from 2000 to 3000 feet

2-3″ above 3000 feet

*Little to no snow accumulation is expected in downslope locations of the Clinch, Powell, and Holston river valleys.  Greatest amounts are expected above 3000 feet in the High Knob Massif.

Christmas Afternoon

High clouds & cold.  WNW winds 5-15 mph, with some higher gusts.  Temperatures varying from 10s to lower 20s in upper elevations to the upper 20s to lower 30s.  Wind chills in the 10s and 20s, except single digits at highest elevations.

The potential for a significant winter storm is being monitored for late in Christmas Week toward New Year’s Weekend.  Stay tuned for later updates.

Weather Discussion ( Stormy Holiday )

Saturday Afternoon Update

Sometimes this UVA-Wise webcam amazes even me, with sun rays showing lingering orographic clouds capping the massif along the horizon saying to all, Welcome To The Christmas Holiday!

To coin a phrase from a Rambo movie, of all things, the High Knob Massif will “draw First Blood” in terms of wonderland transformation into winter tonight into Sunday morning as riming and freezing fog engulf the high country.

The past 28 years shows that is actually more common than not there, but the problem for many lies in the drop of cloud bases to below the elevation of Wise to impact many folks traveling locally and along U.S. 23 ( a major north-south route ) between southern and northern states.  I posted this a couple days in advance, so hopefully it will benefit a few.

The good news, cloud bases will lift off middle elevation terrain by mid-morning Christmas Eve day as air flow trajectories change in advance of a upper air wave and arctic front that will bring snow showers and light accumulations Christmas Eve into Christmas Morn.

Early Friday Afternoon Update

An orographic enhancement precipitation event is about ready to get underway, with long-lived, persistent clouds engulfing upper elevations of the High Knob Massif on a moderate SSW inflow.

*During my past 3 decades of research one of the most important signals of an orographic enhancement event has been the feeder cloud development in advance of a system ( as seen above ).

There are many important ingredients, with another being a moderate-strong inflow.  In this case a positive mountain torque will be generated as the atmosphere pushes against the terrain.

*With orographic enhancement events why does Doppler radar under-estimate precipitation amounts?  One reason is that the radar beam overshoots the orographic cap cloud environment which enriches the amount of precipitation ( rain and/or snow ) reaching the ground as it often falls out of higher altitude seeder clouds which the beam detects.  Precipitation at the surface is often heavier than the radar indicates as elements ( hydrometeors ) pass through the moisture rich cap clouds.

Why do rain gauges typically under report amounts?  A bulk of precip falling during orographic forcing events is wind driven, horizontally, generating often large rain gauge undercatches.  These strong winds likewise cause the rain, like snow, to “drift” such that surface amounts vary greatly over short distances ( as can be seen with snow ).  Rainfall drifts and is impacted by surface drag just like snow in the high country. 

As I have always stated, since I came to understand this aspect, the ultimate challenge is accurately recording and representing the true amount of precipitation which falls in a place like the High Knob Massif. 

There are a ton of weather changes upcoming between Friday and Christmas Morning, and I have tried to outline the major ones with headlines above the forecast.  Chances of a white Christmas remain low, with this being another example where just barely enough snow may fall for some places to officially have a white one ( but for most folks, it does not matter if it is “official” or not as long as some snowflakes are falling and sticking ).

I wish everyone a Happy Holiday & Many Blessings!

Previous Discussion

A stormy period of weather conditions is taking shape for later Friday through Christmas Eve, with a major transition from mild to bitterly cold air.

A large variation in weather conditions was on display Thursday, with a notable upslope-downslope couplet across the High Knob Massif and Black Mountain area on S-SW winds.  Afternoon temps varied from around 40 degrees at summit levels of the High Knob Massif to lower 60s in the adjacent foothills of eastern Kentucky.

The high country of the High Knob Massif was engulfed in clouds throughout the day, with wind chills making conditions feel like 30s ( enhancing above noted differences with adjacent lowlands ).

An orographic forcing setting is taking shape for later Friday through Saturday, with strong winds and wind driven rainfall ( especially at mid-upper elevations ).

Both the NAM and GFS are reasonably close in the position of the main rain band, and IF this positioning verifies then amounts within upper elevations of the High Knob Massif will be significantly higher than models are predicting due to moderate-strong orographic forcing and a pre-existing feeder cloud ( orographic pilatus ).

The potential for strong rises on creeks, as well as for ponding of water in low-lying locations, will have to be respected if this setting verifies as predicted by current forecast model runs.

While antecedent conditions have been much drier than average since November 1, totals have been significantly greater than in the Tennessee Valley with 3.32″ at the City of Norton Water Plant and around 4.50″ on Eagle Knob of the High Knob Massif during the November 1-December 16 period.

After the threat of significant rainfall wanes the first main concern will be a drop in cloud bases with cold air advection and development of northerly upslope flow by late Saturday Night into Sunday Morning.

This could impact travel along the U.S. 23 corridor across Wise County between the Powell Valley Overlook and Pound Gap.

The first chance for any snowflake action will begin early Sunday at highest elevations, with best chances for middle into lower elevations by late Christmas Eve day into the evening hours ( the period when sticking could occur ).  Amounts continue to look light.

Mountain Area Forecast ( Dec 19-21 )

Cloud bases will be dropping and temperatures turning chilly during Wednesday, with latest model trends being suppressed toward the south with rain.  Locations along and to the south of the High Knob Massif-Tennessee Valley Divide will have better rain coverage than locations to the north.  Temperatures should remain above freezing; although, some places in the high country of the High Knob Massif may get close to freezing the coverage of any freezing rain should be localized.

A more significant precipitation producer will develop by Friday into this weekend in advance of much colder air.  A transition to snow will be possible by the Christmas Holiday, but it remains too early to forecast amounts.

Overnight Into Tuesday Morning

Partly-mostly cloudy.  Windy at higher elevations.  Areas of fog.  SW winds 5-15 mph, with higher gusts, along mountain ridges-plateaus below 2700 ft.  SW-WSW winds 10-25 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures in the 30s to low-mid 40s.  Wind chills in the 20s & 30s at upper elevations.

Tuesday Afternoon

Partly-mostly cloudy.  Gusty.  SW-WSW winds 10-20 mph, with higher gusts.  Temperatures varying from the 40s in upper elevations to the mid-upper 50s ( around 60 degrees possible in downslope locations from Pound to Grundy ).

Tuesday Night Into Wednesday Morning

Cloudy with rain developing toward morning.  SW winds shifting N-NNE at 5-15 mph, with higher gusts, overnight into morning.  Temperatures dropping into low-mid 40s.

Wednesday Morning Into The Afternoon

Rain & showers, especially along and south of the High Knob Massif & Tennessee Valley Divide.  Low cloud bases.  NE-ENE winds at 5-10 mph, with higher gusts.  Temps dropping or nearly steady in the 30s to lower 40s ( coldest within upper elevations ).

Wednesday Night Into Thursday Morning

Partly-mostly cloudy.  Chance of evening showers-drizzle.  Light winds.  Temperatures mainly in the 30s, except locally colder in high valleys at upper elevations.

The summation of multiple waves may lead to a major precipitation event developing across portions of the southern Appalachians and Tennessee Valley into this weekend.

Reference History Of Christmases Past

Weather Discussion ( Stormy Pattern )

Tuesday Night Update

An update tonight has removed the threat of freezing rain from upper elevations on Wednesday with most temps now expected to remain above freezing.  The heaviest and most widespread rain is expected to remain south of the area, with locations along and south of the High Knob Massif-Tennessee Valley Divide expected to have best coverage.

Model runs Tuesday night have come into better agreement with the rain shield associated with this initial wave.

A much stronger and more important wave will begin to impact the mountain region Friday into this weekend in advance of cold air.  Stay tuned for updates on what is looking like a heavy rainfall event with orographic enhancement of amounts.

Previous Discussion

A very stormy pattern is taking shape through the rest of December as a major surge of arctic air sinks southward into the United States, setting up a strong temperature gradient and baroclinic zone ( storm track ).

Reference Early Winter 2017 In The High Knob Massif for a look at recent conditions in the high country.

A persistent layer of capping pilatus ( orographic clouds ) were observed Monday across upper elevations in the High Knob Massif.

The first in a series of important upper air waves will begin impacting the mountain region today into Wednesday, with gusty SW winds giving way to developing rain and chilly air with a wind shift to the N-NE.

Cooling with both advection and upslope flow in low-levels will have to be closely monitored Wednesday for the chance that rain will become freezing rain at elevations above 3000 feet, with possible lowering of the freezing level by the late afternoon-evening.  This would be most likely in locations along and north-northeast of the High Knob Massif and Tennessee Valley Divide where air will be forced to rise.

The European and NAM models are showing a potential for some snow to develop where the air may become vertically deep enough to support snow toward the Greenbrier & Roanoke valleys.  In this area a layer of above freezing air looks to hold aloft as the lower levels chills on NW-ENE upslope flow.

By later this week into Christmas week a highly amplified upper air flow pattern will be developing as another surge of positive WAF ( wave activity flux ) perturbs the polar vortex and helps to develop cross-polar flow into the continental USA ( above ).

A huge north-south temperature gradient will develop as brutally cold air drops southward through southern Canada into the northern Plains and upper Midwest, setting up a battle zone to the south.  This spells trouble for many folks planning on traveling for the Christmas Holiday period.

The summation of multiple waves has the potential to generate a major precipitation event over time.  While  some of this will eventually be in frozen precipitation, the positioning of the rain-snow line is yet to be determined.

Stay tuned for updates.

Mountain Area Forecast ( Dec 17-19 )

ALERT For Icy Conditions For Those Traveling Across The High Country of The High Knob Massif During Sunday Afternoon ( December 17 )

Although sections of State Route 619 remained snow covered and locally icy on Saturday, light precipitation ( some snow-mix-rain ) has combined with temperatures falling to around or below 32 F at highest elevations Sunday afternoon.  Caution is Advised.

Conditions were cold and gusty Saturday, but nothing like Sunday with low wind chills being generated by ROARING SSW-SW winds.

Mountain Area Forecast ( Dec 13-14 )

ROARING SSW To SW Winds And Low Wind Chills Will Continue Into The Overnight And Predawn Hours Of Thursday Morning – Caution Is Advised

A fast moving clipper system passing north of the Mountain Empire will continue to generate ROARING winds across the mountain area through tonight into the overnight.

 Wednesday Night Into Thursday Morning

Partly cloudy during the evening, then becoming cloudy with a chance of flurries & snow showers by morning. Windy and cold.  Winds S to SW 15-25 mph, with higher gusts, below 2700 feet.  SSW-SW winds 25-35 mph, with higher gusts, along mountain ridges above 2700 feet.  Winds diminishing after sunrise.  Temperatures varying from upper 10s to lower 20s in upper elevations by morning to the mid-upper 20s to around 30 degrees.  Wind chills in the 10s to low 20s, with single digits high mountain ridges.

Thursday Afternoon

 Partly-mostly cloudy.  Cold.  NW winds generally less than 10 mph.  Temperatures varying from lower 20s in upper elevations to the lower-mid 30s.

Thursday Night Into Friday Morning

Partly-mostly cloudy.  Cold.  Light winds.  Temperatures varying from low-mid 10s in upper elevations to the low-middle 20s.

Weather Discussion ( Windy )

It does not take a meteorologist to tell winds are roaring across the mountains, especially in the High Knob Massif area where an array of beautiful lenticular ( mountain wave ) clouds are being highlighted by sunset.

These strong winds are also continuing the low wind chills.

Although we do not have the mesonet coverage as needed, there is enough data such that there is no excuse for leaving out the Cumberland Mountains in current Wind Advisories.

Note sustained speeds are over 30 miles per hour at high elevations.

These mesonets span the 2774 to 4031 foot elevation zone, in which thousands of people live across Wise, northern Scott, and southern Dickenson counties.

Drop through middle elevations, even into lower elevations below 2000 feet in parts of Wise & Dickenson counties, and these winds are still ROARING since SSW-SW flow is climatologically the windiest in this area.

Snow depths of 2″ to 3″+ occurred with the most recent clipper within upper elevations of the High Knob Massif to Burkes Garden area, with Joe & Darlene Fields measuring 2″ of ground depth ( 1.8″ ) Wednesday in the High Chaparral community ( with 3″ or locally more at highest elevations ).

A morning snow depth of 3″ was also reported in Burkes Garden.  These totals were ironically more than counties within the Winter Weather Advisory ( officially posted by the NWS ); although, Wise County and adjacent high elevation areas were not included!

Roads were slick and snow covered in the high country, with the road on Eagle Knob ( above ) being solidly covered despite much blowing ( horizontal ) snow that generated large depth variations along the high ridges.

Mountain Area Forecast ( Dec 11-13 )

ALERT For Strong SW Winds Into The Overnight In Advance Of Much Colder Air & Snow Squalls

Strong SW winds will continue to ROAR along the Cumberland Mountains into the overnight in advance of a strong cold front.  Caution is advised.

ALERT For Accumulating Snow Tuesday With A Sharp Temperature Plunge Through The Afternoon Into The Evening – Low Wind Chills And Hazardous Conditions Are Expected – Especially Along & North to Northwest Of The High Knob Massif and Tennessee Valley Divide

An Arctic Cold Front will push across the mountains Tuesday and will be accompanied by snow showers, flurries, snow squalls and sharply dropping temperatures and wind chill factors.  Moderate to strong orographic forcing and increasing instability aloft will create whiteout conditions at times.  Widespread snow is expected along and north to northwest of the High Knob Massif-Tennessee Valley Divide, with more scattered activity in downslope locations to the southwest and southeast.

Monday Night Into Tuesday Morning

Partly to mostly clear through the evening, then increasing overnight clouds with a chance of flurries & snow showers developing around sunrise.  Windy.  Winds SW-W at 15-25 mph, with higher gusts, along mountain ridges & exposed plateaus below 2700 feet.  Winds SW to WNW at 20-30 mph, with higher gusts, along mountain ridges above 2700 feet.  Rapid evening temperature drop in sheltered valleys, then temps rising overnight with mixing.  Turning colder at mid to upper elevations by sunrise.  Temperatures dropping into the lower 20s to lower 30s.  Wind chills falling into the 10s and 20s, except single digits toward morning on highest mountain ridges.

Tuesday Morning Through The Afternoon

Snow showers, flurries, and snow squalls.  A whiteout snow burst possible along the Arctic Front, then hit-miss bursts of heavy snow possible through the afternoon.  Windy and turning bitterly cold.  WNW-NW winds 10-25 mph, with higher gusts.  Temperatures falling through the 20s at middle-lower elevations, and through the 10s at upper elevations above 3000 feet.  Wind chills dropping into single digits and 10s in middle-lower elevations and to below zero across upper elevations ( as low as -10 degrees below zero possible on highest peaks by late ).

Tuesday Night Into Wednesday Morning

A chance of snow showers, flurries, and localized squalls through the evening, then partial clearing possible by the predawn to sunrise period.  Windy & bitter cold.  WNW-NW winds 10-20 mph, with higher gusts.  Temperatures in the 10s, with single digits at upper elevations.  Wind chills in the 0 to 10 above range at middle elevations and in the 0 to -10 degree below zero range at upper elevations ( except locally -10 to -20 below on highest peaks in gusts ).

Widespread snow accumulations of 1-2″ are expected along and to north-northwest of the High Knob Massif-Tennessee Valley Divide, with locally higher amounts of up to 3″+ in locales experiencing numerous squalls or snowstreaks.

More scattered snow amounts are expected in downslope locations from Big Stone Gap through central-western Lee County, southward into the Great Valley of northeastern Tennessee and southwestern Virginia.

Weather Discussion ( Arctic Front )

A simply gorgeous sunset was observed Sunday following a round of mostly light snow that dropped a dusting to 1″ on the mountain area into early Sunday.

Strong winds and low wind chills over the high country on Sunday were generating an array of nice orographic wave clouds.  A few being observed from UVA-Wise near sunset.

High resolution visible imagery Monday revealed lingering snow from the southern snowstorm that dropped rare and impressive amounts of snow far to the south.

I have just updated my forecast for an ALERT to cover the Strong SW winds which are roaring across the mountains.

While strong winds were already in my forecast for tonight, wind speeds at mid-upper elevations have increased above what were predicted earlier, with 40-50+ mph gusts, so an ALERT is needed for locations where many people live.

As often occurs, with mountain wave formation, strong gusts are penetrating down to valley floors in the Pound-Clintwood corridor ( this is not recognized beyond myself so it must not really occur ). 

The main focus beyond these roaring winds tonight will be bitterly cold air pouring into the mountains Tuesday, along with moderate-strong orographic forcing and increasing vertical instability as very cold air aloft steepens the lapse rates through Tuesday afternoon.

A WINDEX event is developing into Tuesday and conditions along and west-northwest of the lifting zones of the High Knob Massif and Tennessee Valley Divide, which includes most all of Wise-Dickenson counties, are going to get bad with whiteout conditions at times in addition to plunging temperatures and wind chill factors ( this despite the lack of recognition officially ).

Due to very cold air aloft, some intense squalls may also spill over into the Great Valley.

*Tuesday will be nothing like the Saturday Night into early Sunday period and any forecaster who thinks it will needs to return to school for more training!

Mountain Area Forecast ( Dec 9-11 )

The Coldest Air Of This Early Winter Season Will Arrive Tuesday Into Wednesday Morning.  An Alert For Bitterly Cold Air And Accumulating Snow Will Likely Be Needed.  Snow Squalls With Whiteout Conditions Will Be Likely Tuesday – A New Forecast Will Be Issued Monday PM ( Stay Tuned For Updates ).

Previous Alert

Accumulating Snow From A Clipper System Will Be Likely Saturday Night Into Sunday Morning In Upslope Locations On W-NW Air Flow

A clipper system will cause snow showers and flurries to develop by Saturday evening, with a burst or two of snow possible.  Windy and bitter conditions will accompany a drop in temperatures.

Snowfall accumulations from 0.5″ up to 1-2″ are expected, with greatest amounts in upslope locations with respect to W-NW air flow.  Little to no snow accumulation is expected in downslope locations.  While locally higher amounts could occur in the High Knob high country, the moisture tap from the Great Lakes will be limited, the system fast moving, and the time for accumulations of relatively short duration to help limit amounts.  This will be a dry ( low density ) fluff in contrast to the wet snow that fell over the Tennessee Valley and Blue Ridge during December 8-9 AM.

Saturday Afternoon

Partly to mostly sunny then becoming cloudy with a chance of snow showers or flurries by late. Cold.  SSW-WSW winds 5-15 mph, with higher gusts.  Temperatures varying from the mid-upper 20s in upper elevations to mid-upper 30s.  Wind chills in the 10s & 20s ( coldest highest elevations ).

Saturday Night Into Sunday Morning

Windy & colder with snow showers & flurries.  Winds W-WNW at 10-20 mph, with higher gusts ( especially along mountain ridges ).  Temperatures dropping into the low-mid 10s to lower 20s ( coldest highest elevations ).  Wind chills in the single digits and 10s, except below zero in gusts along high mountain ridges.  Rime formation highest peaks.

Sunday Afternoon

Partly cloudy.  Gusty & cold.  SSW-WSW winds 10-20 mph, with higher gusts.  Temperatures varying from the mid-upper 20s in upper elevations to the mid-upper 30s.  Wind chills in the 10s and 20s, especially along mountain ridges and exposed plateaus.

Sunday Night Into Monday Morning

Partly cloudy to clear.  Windy.  SW winds 5-15 mph, with higher gusts, along mountain ridges-plateaus below 2700 feet.  WSW-WNW winds 15-25 mph, with higher gusts, on mountain ridges above 2700 feet.  Temperatures mainly in the 20s to lower 30s.  Wind chills in 10s to low 20s, except single digits  in gusts along high mountain ridges.

Weather Discussion ( Rare Event )

Bare ground from the High Knob Massif to Snowshoe and Canaan Mountain early Saturday marked a rare event for these 100″+ a year snowfall summits, as snow covered the landscape only miles to the east and southeast.

The summit of the High Knob Massif had rime but only a trace of snowfall during Friday into Saturday Morning ( December 8-9 ).

The first official 1″ of snow was recorded in the Tri-Cities, with more in places like Johnson City, versus a barren land within the Norton-Wise and High Knob Massif area.

Although this gradient ( difference ) in snowfall was expected, it is still rare for the High Knob Massif and Snowshoe-Canaan to be shut-out during such a system.

Some of the greatest reports in GIS Format

As much as 15-18″ of snow was reported in southwestern portions of North Carolina, with locally 10-12″ in parts of Georgia and Alabama.  Snow even fell on Pensacola in the Florida panhandle, as well as in Brownsville, Texas.

Although less snow fell in Grayson Highlands State Park than in locations farther southwest along the Blue Ridge, the scene is still plenty wintry at the 4,000 foot level.

Mountain Area Forecast ( Dec 8-10 )

ALERT For Accumulating Snow Friday Into Friday Night – Especially Along & South of the High Knob Massif and Tennessee Valley Divide

An increasing gradient of snowfall is likely from northwest to southeast across the area, with limited snow along and north to northwest of a Pennington Gap to Clintwood line where little snow is expected to accumulate through Friday Night ( less than 1″ ).

A zone along the Tennessee Valley Divide, including Norton-Wise, Banner Mountain, Sandy Ridge, and adjacent communities could see 1″ or more of snow, with heavier snow more likely from the High Knob Massif south & southeast across the Tennessee Valley toward the Blue Ridge ( general 1″ to 4″ ).  A rare setting where more snow may fall in the Tri-Cities than in Norton-Wise. 

The heaviest snow, with 4-8″+, will be likely along and east of the Blue Ridge and Tennessee-North Carolina border.

Only a slight shift in the track of this system could change the placement of these amounts, but the general increase in snowfall from northwest to southeast will hold.

Friday Morning Through This Afternoon

Cloudy with morning flurries giving way to developing snow, especially along and south of the High Knob Massif and Tennessee Valley Divide.  Light winds.  Temperatures varying from upper 10s to lower 20s highest elevations to the upper 20s to lower 30s.

Friday Night Into Saturday Morning

Cold with periods of snow, especially along and southeast to east of the Virginia-Kentucky stateline into the overnight before tapering to flurries.  Light winds becoming W-NW.  Temperatures varying from low-mid 10s to low-mid 20s, coldest at highest elevations.  Wind chills in single digits within highest elevations.

My Mesoscale Discussion

Moisture From A Southern System And Front Over The Southeastern USA Will Transport Moisture Into Cold Air In Place Over The Southern Appalachians During Friday Into Early Saturday AM With Widespread Snow Accumulations.  A Sharp Cut-off Will Be Likely Along The Western & Northwestern Side Of This System.

This is an evolving situation with only a small shift in the track of the main moisture band having large implications on the snowfall potential across the Mountain Empire.  As of late Thursday Night a small but notable westward shift was occurring in models, and I expect this could continue due to the formation of the Right Rear Quadrant Entrance Region Of A 250-300 MB Jet Streak.  Upper air divergence beneath this region could allow snowfall to build west to the High Knob Massif & Tennessee Valley Divide and will need to be closely monitored during the next 12-24 hours.

The GFS Model is farther west than the 00z European with the core of this developing Jet Streak, and the NAM 12 KM Model is also a little farther west than the European despite having a moisture field farther east.  Thus, given this is a developing Jet Streak, there is significant potential for a continued westward shift in accumulating snowfall across the Tennessee Valley toward the Virginia-Kentucky stateline during Friday into Friday Night.

**Cross-isobaric ageostrophic circulation developing within the right-rear entrance region of the jet streak will be the synoptic mechanism capable of forcing a westward shift; albeit small, in the snowband extent.  This often has some natural interaction with the three-dimensional terrain.  Past climatology of similar systems dictates that locations along and southeast of the VA-KY border are typically at highest risk for expansion beyond what most models tend to indicate.

In this case, only time will tell exactly where the western edge of 1-3″+ of sticking snow sets up Friday into Friday Night.  New runs of models overnight into Friday will be important to monitor.

The coldest air is along the west side of the Appalachians such that any moisture reaching this area will have a lower snow density ( higher snow to water ratio ) than locations farther east and southeast.  Drier air is also over this area, thus the battle will be on between lift and drier air.  If the synoptic-scale lift becomes strong enough it will allow the snowband to build west more than models currently show, while if the synoptic-scale lift is weaker then the snowband will remain farther east.

Odds for 3-6″ of snow are high for locations along and east of the Tennessee-North Carolina border, with 1-3″ toward the west.  At this time the westward extent remains in play and could cover the Tri-Cities, and could reach as far west-northwest as the Virginia-Kentucky line.

A second system will drop into the developing upper air trough and phase with southern energy to form a large storm for the East Coast.  Note how close it is to phasing over the southern Appalachians.

A tap of some Great Lake moisture will combine with this to generate snow showers, flurries, and possibly a burst or two of snow Saturday Night into Sunday AM, with best accumulations expected along the front range of the Cumberland-Allegheny mountains.

A general 1″ to 2″ of dry snow will be possible along and north to northwest of the High Knob Massif & Tennessee Valley Divide during Saturday Night into Sunday AM.  The main unknown, will this be on top of any prior snow from the southern system?