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?

Mountain Area Forecast ( Dec 5-8 )

A period of accumulating snow will be possible late Saturday into Sunday AM ( December 9-10 ), especially in locations along & north-northwest of the High Knob Massif and Tennessee Valley Divide, with a new surge of bitterly cold air.

Overnight Into Tuesday Morning

Becoming cloudy.  Windy, especially along mid-upper elevation mountain ridges.  Large vertical temp spread through early overnight between sheltered valleys and exposed ridges.  SSE-SSW winds 10-20 mph, with higher gusts, below 2700 feet.  S to SW winds 15-30 mph, with  gusts over 40 mph, on mid-upper elevation ridges.  Temps varying from 30s in colder valleys to the mid 40s to mid 50s along mountain ridges & exposed plateaus.  Wind chills in the 30s along upper elevation mountain ridges.

Tuesday Morning Through The Afternoon

Cloudy & windy with rain developing.  Local downpours. Winds SSW-WSW at 10-25 mph, with higher gusts.  Turning cooler by late.  Temperatures varying from low-mid 40s to the low-mid 50s.  Low cloud bases with dense fog at upper elevations.  Wind chills in the 30s along upper elevation mountain ridges.

Tuesday Night Into Wednesday Morning

Partly-mostly cloudy.  A chance of flurries.  Turning colder. Winds WNW to NW at 5-15 mph, with higher gusts.  Temps from low-mid 20s to lower 30s.  Wind chills in the 10s and 20s, except single digits in gusts at highest elevations.

Wednesday Afternoon

High clouds.  Cold.  Winds SW-W at 5-10 mph, with some higher gusts.  Temperatures varying from upper 20s to lower 30s in upper elevations to upper 30s and lower 40s.  Wind chills in the 20s to lower 30s on mountain ridges, except 10s in stronger gusts at highest elevations.

Wednesday Night Into Thursday Morning

Mostly cloudy ( high clouds ) and cold.  Winds WSW-WNW at 5-15 mph, with higher gusts.  Temperatures widespread in the 20s to around 30 degrees.  Wind chills in the 10s & 20s, coldest at highest elevations.

Thursday Afternoon

Partly to mostly cloudy.  Cold.  Winds WSW-WNW at 5-10 mph, with some higher gusts.  Temperatures varying from upper 20s to lower 30s in upper elevations to the upper 30s to lower 40s.

Thursday Night Into Friday Morning

Mostly cloudy.  A chance of flurries.  Cold.  Winds WNW-NNW at 10 mph or less.  Temperatures varying from the lower-middle 10s to the low-middle 20s.

A very cold pattern is taking shape for the eastern USA, with this initial push of cold air being only seasonably cold.  Increasingly cold air, with potential for extreme cold, is being monitored for this weekend into the next 1-2 weeks in separated surges.

Weather Discussion ( Harsh Potential )

Late Tuesday Evening Update

Only a few changes to this update, including the addition of a word of caution for everyone to be watchful of icy patches on any above ground or outdoor surfaces that remain wet as temperatures continue to drop overnight.

As of Midnight temps had fallen into the middle 20s at highest elevations, in clouds, with wind chills dropping to around or below 10 degrees in gusts ( temps at the summit of High Knob tend to run a couple degrees colder than this live data from the Black Mountain mesonet ).

Rainfall with Tuesday’s cold frontal boundary averaged 0.75″ to 1.25″ over the High Knob Massif, and along higher portions of the Tennessee Valley Divide, with lesser amounts elsewhere.

The main change to Wednesday is to increase cloudiness, as it looks like it may be difficult to shake the high clouds as tonight’s frontal system stalls far to the south.  This will make it a chore for many places to get out of the 30s in upslope locations along and west to southwest of the Tennessee Valley Divide and High Knob Massif.

Previous Discussion

Although only seasonable cold is expected to arrive this week, the upper air flow pattern taking shape across North America during the next 1-2+ weeks has serious potential to turn harsh, with December 1989 being a top analog for this point in time ( differences may; however, result in a varied outcome by January 2018 versus January 1990 ).

Reference Early Winter 2017 In The High Knob Massif Area as I recap November 2017 statistics ( adding more as I get time ).

A majestic sunset graced December 4, with strong S-SW winds at mid-upper elevations being the only negative factor to signal changes upcoming.

These strong winds were putting a chill into the air at high elevations, in the High Knob high country and atop adjacent Black Mountain, where temperatures were in the 40s.

Strong winds will continue overnight into Tuesday ahead of a powerful cold front with a band of rain.  Winds will tend to mix downward through middle into the lower elevations over time as the front gets closer, with rises in temps being possible in sheltered valleys that decoupled late Monday.

A band of rain, with local downpours, will arrive Tuesday with orographic enhancement of rain being possible from the High Knob Massif and Tennessee Valley Divide south and southwest ( downslope reduction in leeside zones ).

I see a progressively colder and more wintry pattern taking shape during the next week to 10 days, with any snow that may eventually fall and accumulate helping to enhance the potential for harsh conditions.

The upper air pattern taking shape during the next week to ten days is simply classic for increasing cold, with a series of progressively colder air masses likely to impact the region and eastern USA during the next 1-2+ weeks.

The upcoming pattern is analogous to that observed during December 1989, which featured a 60 degree MAX temp in Clintwood on December 6 prior to the bottom dropping out.

No two seasons are exactly alike, but certainly some do make better analogs than others and December 1989 is a  top analog for this current point in time.

The mean of the European ensemble group has been strongly suggesting that this pattern locks in with a progressively colder nature during the next 1-2 weeks.

Although lovers of snow may be disappointed initially, the pattern and ensemble MEAN are also suggesting that snow chances will increase through next week.  If snow cover is established then there is NO DOUBT that a pattern like this will turn harsh.  Stay tuned for updates.