Weather Headlines

ALERT For Strong Winds Developing Thursday Night Into Friday Morning At Upper Elevations And Locally In Lower Elevations With Mountain Waves

An increasing pressure gradient will generate strong SE to SSE winds across the mountain area late Thursday into Friday morning as rain develops. Winds will be strongest along high mountain ridges and within locations leeward of them where mountain waves will become active.

An inversion within the 875-850 MB layer will be conducive to breaking mountain waves, with reflection of strong winds downward into favored locations from Powell Valley and Pine Mountain in Wise County, and the Clinch Valley of Russell & Tazewell counties, into the Camp Creek and Cove Mountain areas of eastern Tennessee. Wind gusts of 40-60+ mph will be likely in the impacted locations.

*Bitter air through tonight into Wednesday morning will feature the coldest temperatures of the season to date in mountain valleys.

Snowfall at highest elevations in the lifting zone of the High Knob Massif ended up being more significant than expected, with large dendritic snowflakes adding to a two-day snowfall total of around 4″ (up to 6″+ in drifts).

While this pushes the seasonal snowfall tally to nearly 30″ at highest elevations in the massif, it has mostly been a “nickel-dime” type of scenario with no storm since December 2018 producing more than a foot of depth in the high country.**

**When not including drifting. The current season to date tally is much below the longer-term average.

At middle to lower elevations, snow accumulated and sublimated-melted during the 2-day event with less total depth than observed at upper elevations. Snowfall was widespread and roads became slick to result in schools closing in Buchanan, Dickenson and Wise counties into morning hours of 21 January.

The official 2-day snowfall tally reached 1″ in Clintwood, at 1560 feet elevation, to exemplify how light the event was for much of the area as the snow drought officially continues onward given one must go all the way back to the 8-10th period of December 2018 to find a snowfall with more than 4″ of snow depth in Clintwood***.

***A 1-3 December 2019 storm featured the last snow with more than 4″ of depth in the High Knob Massif. The big snow of December 2018 was the last major snowstorm event for the region in general, with 18″-24″ of snow in upper elevations of the High Knob Massif.

Most of Virginia did not have any snowfall, at least none to accumulate, and few to no clouds during the past 48-hours (20-21 January 2020) with both clouds and snow restricted to lifting zones with respect to NW-NE air flow trajectories. Most of Virginia rests leeward of the eastern West Virginia highlands, under downslope flow, on air flow trajectories possessing WNW-N trajectories, with the exception being far southwestern Virginia.

Short-Term Forecast

Tuesday Night Into Wednesday Morning

Mostly clear. Large vertical temperature spread between bitter cold valleys and rising readings on upper elevation mountain ridges. Light N-NE winds, except 5 to 10 mph with some higher gusts on mid-upper elevation ridges. Temperatures in the single digits and 10s, with extremes varying from near 0 degrees (F) or locally below in upper elevation valleys (from the High Knob Massif to Burkes Garden) to readings rising through the 20s along upper elevation mountain ridges.

A 20 to 30+ degree vertical temperature difference is expected to develop into Wednesday morning between colder mountain valleys and higher mountain ridges where warm air advection will begin (initially enhancing low-level drying). Coldest temperatures will develop in upper elevation basins from the High Knob Massif to Burkes Garden where colder sites could drop below 0 degrees (F). The potential for classic Appalachian frost pockets sites, Big Cherry Lake Basin and Burkes Garden, to drop well below zero exists given temperatures at 7:30 PM (21 January) have already fallen into single digits in these colder locations.

Shady Valley is a classic frost pocket location in northeastern Tennessee, but it tends to run warmer (on average) than the Big Cherry Basin and Burkes Garden.

Wednesday Afternoon

Increasing high clouds. Milder. Winds E-SSE at generally less than 10 mph. Temps varying from 30s to lower 40s to the mid-upper 40s (warmest in valleys of the Clinch, Powell and Holston).

Wednesday Night Into Thursday Morning

High clouds. Winds SSE-SSW at 5-15 mph, with higher gusts, on middle elevation mountain ridges and exposed plateaus below 2700 feet. Winds S-SW 10-25 mph with higher gusts on mountain ridges above 2700 feet. Temps varying from 10s to low 20s in colder mountain valleys sheltered from wind to 30s along breezy-gusty mountain ridges. Wind chills in the 10s and 20s on ridges above 2500-3000 feet.

Thursday Afternoon

Mid-high clouds. Winds SSE-SSW at 5-20 mph with higher gusts, especially along middle-upper elevation mountain ridges. Temperatures varying from lower 40s at upper elevations to the upper 40s to lower 50s. Wind chills in the 30s to lower 40s, except 20s possible within stronger gusts on highest peaks.

Thursday Night Into Friday Morning

Increasing and lowering clouds with rain developing. Winds SE-SSE 10-20 mph, with higher gusts, on mountain ridges & plateaus below 2700 feet. Winds SSE-S at 15-30 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures varying from 30s to lower 40s (coldest at highest elevations). Wind chills in the 20s and 30s (coldest upper elevation mountain ridges).

Precipitation may begin as snow, frozen or mixed precipitation along the eastern slopes of the Blue Ridge. Any snow on highest peaks will tend to change to rain as potential frozen precipitation continues at lower elevations on easterly flow before eventually being overwhelmed by warm air advection.

Friday Morning Through The Afternoon

Rain and rain showers, wind driven at mid-upper elevations. A chance of thunder. Local downpours, especially within upslope locations along and south-southeast of the High Knob Massif and Black Mountain corridor. Becoming showery and more scattered. Windy. SE-SSE winds 10-25 mph, with higher gusts, shifting SW by late afternoon. Temps in the 30s to lower-middle 40s (coldest at high elevations). Cloud bases lowering to obscure upper elevations. Wind chills in 20s and 30s (coldest at highest elevations).

Following a break in activity by late afternoon-early evening, an influx of low-level moisture on SW-WSW flow will lower cloud bases in lifting zones along the High Knob Landform and Black Mountains. Locations along and southwest of the High Knob Massif & Tennessee Valley Divide will need to monitor for dropping cloud bases that could impact locations from Wise southwest through Little Stone Mountain Gap (Powell Valley Overlook), along the U.S. 23 corridor, during Fright night into the overnight hours of Saturday (January 24-25 period).

Friday Night Into Saturday Morning

Lowering clouds with rain showers redeveloping and becoming mixed with or changing to snow at middle-lower elevations. Changing to snow upper elevations. Turning colder. Winds SW-WSW at 5-15 mph with higher gusts. Temperatures dropping into the mid-upper 20s at upper elevations and the 30s at middle-lower elevations. Wind chills falling into the 10s and 20s, except single digits in gusts toward morning on highest ridges. Accumulations up to 1″ above 3000 feet. Riming developing at elevations above 3000-3300 feet.

Moisture wrapping around a upper-level low, which includes some Great Lake moisture transport, will cause light snow and flurries to develop Friday night into Saturday. Light snow and flurries, along with possibly a few heavier snow showers, will be possible at times through much of the weekend into early Monday. Accumulations are expected to be light, continuing the current trend, with a dusting up to 3″ (greatest at high elevations).

Saturday Morning Through The Afternoon

Cloudy and cold. Intervals of light snow, flurries and heavier local snow showers. Winds SW to W at 5-15 mph, with higher gusts. Temperatures holding nearly steady, in the 20s at upper elevations and 30s to near 40 degrees at middle-lower elevations. Low cloud bases with riming at highest elevations. Wind chills varying from 10s at the upper elevations to the 20s to lower 30s.

Saturday Night Into Sunday Morning

Cloudy and seasonally cold. Intervals of light snow and flurries. Heavier local snow showers possible. Winds SW to W at 5-15 mph, with higher gusts. Temps varying from upper 10s to upper 20s to around 30 degrees. Low cloud bases with riming at upper elevations. Wind chills from single digits at highest elevations to the 10s & 20s.

Extended Forecast Period

Will the southern Appalachian snow drought ever end? Yes, of course it will. But, when?

When I say snow drought I am not referring to the observed trend in downslope locations where a single snow event, such as in December 2018, can skew an entire season. A regression on the past 16 seasons for the Tri-Cities, as an example, reveals an increasing snowfall trend during this short-term period.

Regressing the same period for Mount LeConte, Wise, Clintwood, Burkes Garden and the High Knob Massif all reveal a decreasing short-term trend, especially strong, of course, since the 2015-16 winter season, for the same period that downslope sites like TRI show increases.

**Burkes Garden contains the longest climate record for any station in southwestern Virginia and was selected to illustrate the longer-term trend.

Regressing the past 121 years, using Burkes Garden, reveals an increasing snowfall trend during the long-term but not since 2003-04 (the TRI period illustrated).

With the above noted, a better looking pattern (on paper) should raise hope for snow lovers in the late January to early February period.

A review of 90 ensembles during the 1200 UTC model runs of January 23, for example, found 38 predicting 6″ or more of snow in the Wise area between now and the end of the first week of February (42%). While that is still less than 50%, it is a higher percentage than observed for a long time and at least offers a stronger potential for one or more significant snowfall events.

GFS Ensembles are most bullish, and show the highest percentage, at least, on the morning run of January 23.

Until a major winter storm develops and drops deep snow, of course, always doubt while in snow drought.

Reference Mid-Winter 2020_High Knob Massif

Although moisture in upslope locations has been abundant since the beginning of Meteorological Winter, the mean storm track has kept the Mountain Empire and much of the eastern USA on the warm side of synoptic-scale storm systems which is unfavorable for significant falls of snow, especially given wrap-around flow into the upslope locations have more often than not lacked any significant Great Lake moisture transport.

Time will tell if the upcoming pattern can finally change this, with a wave during late January-early February offering the first potential. Stay tuned for updates.

Weather Headlines

*Cloudy and cold conditions, with light snow-flurries, will continue through Monday night into early Tuesday before much drier low-level air arrives. Sub-zero wind chills will continue at highest elevations, with single digits and 10s at lower-middle elevations. Caution is advised.

Update_11:30 PM Monday…Despite anticyclonic flow a plume of low-level moisture transport from the Great Lakes will continue widespread light snow, flurries, and locally heavier snow showers through the overnight into Tuesday morning (most widespread in locations along and west of the Cumberland-Allegheny Front which includes Buchanan, Dickenson & Wise counties in Virginia). Accumulations from a dusting to 1″ of low density snow will be common.

Expect slick road conditions at upper elevations, with increasing slick areas into middle to lower elevations.

Monday Afternoon Update

Roads are snow covered at highest elevations in the High Knob Massif, with slick spots possible or becoming possible on other roads at lower elevations through Monday night in locations along & north-northwest of the Cumberland-Allegheny Front.

A general 1″ to 2″ of low density snow fell at upper elevations in the High Knob Massif, above 3300 feet, with slick morning road conditions above 2500-3000 feet. Rime formation was also observed to mark 30 days with riming since the start of this winter season (rime deposition acts as an important secondary input of moisture to the annual water budget within upper elevations).

The Monday morning drive to work along State Route 706, courtesy of RN Darlene Fields. Wind blown, low density snow easily blew across roadways, despite sublimation which was a much bigger factor than melting amid single digit air temps.

Air temperatures Monday have struggled to break 10 degrees on High Knob, and 20 degrees in Wise, with colder wind chills.

*Cold and gusty NW-N winds will generate bitter wind chills, with single digits and 10s being widespread into Monday. Sub-zero wind chill factors will occur in the upper elevations. Caution is advised.

*Flurries and light snow, with a few snow showers, will be observed through Sunday night into early Monday, especially along and northwest of the High Knob Massif-Tennessee Valley Divide (Cumberland-Allegheny Front). A chance of flurries-light snow will continue to Tuesday.

A little moisture transport from the Great Lakes will support flurries and light snow, but any accumulations are expected to be light in the southern Appalachians with a dusting up to 1″ being possible.

*Cold temperatures will continue through the middle of this week, with prime cooling conditions in mountain valleys during Tuesday night into Wednesday AM. The only missing ingredient (for this time of year) being significant snow depth.

Appalachian frost pockets will be coldest into Wednesday morning, with classic locations from the High Knob Massif to Burkes Garden having the potential to reach 0 degrees (F) or below. Coldest temperatures observed to date in these locations have been in the 0 to 5 above range, so Wednesday AM has a good opportunity to produce the coldest MINS so far this season in these places.

Short-Term Forecast

Overnight Into Monday Morning

Cloudy with flurries and light snow. Bitter. Gusty NW-N winds 5 to 15 mph, with higher gusts on middle to upper elevation mountain ridges and exposed plateaus. Temps dropping into the 10s, with single digits across the upper elevations. Wind chills varying from single digits and 10s at mid-lower elevations to sub-zero at upper elevations, locally colder than -10 degrees (F) upon highest peaks. Riming on highest peaks Snow accumulations from a dusting up to 1″ .

Widespread light snow and flurries will occur with upsloping NW-N low-level flow into the western front range of the Appalachians, along and NW-N of the High Knob Massif and Tennessee Valley Divide (Cumberland Front) in southwestern Virginia and the Allegheny Front in West Virginia. Accumulations of a dusting to 1″ will be widespread, with higher amounts along the eastern-northern West Virginia highlands and locally at highest elevations of the High Knob Massif.

Monday Afternoon

Partly to mostly cloudy. Chance of flurries and light snow showers. Cold. Northerly winds 5 to 15 mph with some higher gusts. Temperatures varying from low-mid 10s to the mid-upper 20s (coldest at highest elevations). Wind chills in single digits and 10s, except sub-zero at highest elevations.

Monday Night Into Tuesday Morning

Mostly cloudy. Flurries, light snow and snow showers. Winds N-NE at 5 to 10 mph with higher gusts. Continued cold with temps in the single digits and 10s (coldest in upper elevations). Wind chills varying from sub-zero upper elevations to the single digits & low 10s. Accumulations of a dusting to 1″ .

Despite anticyclonic flow, a plume of Great Lake moisture will produce widespread light snow and flurries along the upslope side of the mountains with respect to N-NE flow. Due to cold temperatures, slick road conditions will be a factor. Much drier low-level air is then expected to advect into the area during Tuesday on anticyclonic flow.

Tuesday Afternoon

Becoming sunny. Seasonally cold. N-NE winds 5-10 mph with higher gusts. Temperatures varying from the lower 20s to the lower 30s (coldest highest elevations). Wind chills in the 10s and 20s, except single digits in gusts on highest peaks.

Tuesday Night Into Wednesday Morning

Mostly clear. Large vertical temperature spread between bitter cold valleys and rising readings on upper elevation mountain ridges. Light N-NE winds, except 5 to 10 mph with some higher gusts on mid-upper elevation ridges. Temperatures in the single digits and 10s, with extremes varying from near 0 degrees (F) or locally below in upper elevation valleys to readings rising through the 20s along upper elevation mountain ridges.

A 20 to 30+ degree vertical temperature difference is expected to develop into Wednesday morning between colder mountain valleys and higher mountain ridges where warm air advection will begin (initially enhancing low-level drying). Coldest temperatures will develop in upper elevation basins from the High Knob Massif to Burkes Garden where colder sites could drop to near or below 0 degrees (F).

*The potential for a couple of winter storm events is being monitored for next weekend (January 25-26), and toward the end of January-early February.

Weather Headlines

ALERT For Strong S-SW Winds Developing Overnight Through Saturday Afternoon

Strong SW winds blowing now at upper elevations in the High Knob Massif will increase overnight into Saturday and mix downward across middle into the lower elevations. Wind gusts of 30-50 mph will become widespread, with higher gusts to hurricane force at highest elevations in the High Knob Massif. Local tree damage and power outages will be possible.

*Seasonally cold conditions will be felt tonight through Friday night

*An alert for High Winds will be likely for Saturday (January 18)

*A colder pattern next week features arctic air from Sunday through early week

*The Snow Drought (from 2019) looks to continue with light amounts expected at this time. A few ensemble members are predicting significant snow, but the majority are not. Stay tuned.

Short-Term Forecast

Thursday Night Into Friday Morning

High clouds. NW-NE winds 5-15 mph, with some higher gusts, on mid-upper elevation mountain ridges-plateaus. Temps falling into the 20s, except 10s within the colder mountain valleys and on coldest mountain ridges. Wind chills falling into the 20s, except single digits and 10s on mid-upper elevation mountain ridges (locally sub-zero on highest peaks, such as at the High Knob Lookout).

Cold air transport will continue near the surface into early hours of Friday (the coldest transport centered around 925 MB) as warm air advection begins aloft (high clouds), and on highest mountain ridges into sunrise. Turbulent mixing will oppose decoupling, but frictional terrain drag below an increasing inversion within the 875-775 MB layer should allow many valleys to decouple with developing drainage flows into the overnight.

Increasing high clouds aloft will hinder OLR into the predawn-sunrise period, such that cooling conditions will not be ideal despite the advected presence of very dry (very low dewpoint) air within cold air drainage source locations of the higher mountain terrain during Thursday night into Friday morning.

Friday Afternoon

High & mid-level clouds. Seasonally cold. Easterly winds becoming SE to S at 5-10 mph, with higher gusts. Temps varying from the 30s to low-mid 40s. Wind chills in the 20s and 30s on higher mountain ridges.

Friday Night Into Saturday Morning

Cloudy. A chance of freezing rain or sleet by morning. Becoming windy (beginning on highest ridges and mixing downward into middle-lower elevations into morning). Large vertical temperature spread developing initially between decoupled mountain valleys (light to calm winds) and increasingly windy mountain ridges.

Strong evaporative cooling in a dry low-level air mass will have the potential of causing enough cooling for freezing rain and/or sleet-snow at the onset of precipitation. This will be especially true if precip onset is early Saturday. A more widespread array of frozen precipitation is expected initially along the eastern slopes of the Blue Ridge (reference any SPS or advisories).

SSE-S winds increasing to 10-25 mph, with higher gusts, on mountain ridges & exposed plateaus below 2700 feet. S-SW winds 20-35 mph, with higher gusts, on mountain ridges above 2700 feet. Temps mainly in the 30s, locally colder in sheltered valleys and highest windward facing mountain ridges. Wind chills in the 20s and 30s, except 10s at highest elevations.

Saturday Morning Through The Afternoon

Windy. Rain showers developing. Local downpours, especially in upslope locations. S-SW winds 15-35 mph, with higher gusts (gusts over 50 mph will be possible). Temperatures varying from the upper 30s to upper 40s. Wind chills in the 20s and 30s (coldest high elevations). Areas of fog developing, becoming widespread at high elevations during afternoon-early evening).

Rain will be wind driven in strong upslope flow at mid-upper elevations. This will enhance rain amounts within orographic forcing zones of the High Knob Massif-Black Mountain corridor.

Saturday Night Into Sunday Morning

Windy and turning colder. Evening showers, then a chance of flurries and light snow showers overnight into morning. SW winds shifting WNW at 10-25 mph, with higher gusts. Temps dropping into the middle 10s to mid-upper 20s (coldest at highest elevations). Wind chills single digits and 10s (sub-zero in gusts along highest peaks).

Wind chills will become dangerous to those unprepared at mid-upper elevations during Sunday into Monday. Caution is advised. Riming is expected at highest elevations during much of this period.

Extended Forecast Period

A push of bitter arctic air will arrive this weekend into early next week, with cold air advection beginning Saturday Night into Sunday (January 18-19).

Although some snow showers and flurries will be possible, a Great Lake connection may be too short-lived for significant snow in upslope locations of the southern Appalachians. This will be a trend to follow, given that the Great Lakes are essentially ice free and could be very productive snow squall-plume producers with the right, prolonged flow pattern (which has been limited for the southern Appalachians from last winter up to now).

The coldest air mass will be in place Monday into early Tuesday (January 20-21), with single digits on upper elevation mountain ridges (not including wind chills). Snow cover would make this much more potent, while the lack of snow will help moderate the air mass.

The European Model predicts a rebound to above average temperatures by the middle to end of next week. This is due to a progressive air flow pattern across the Northern Hemisphere, with no high latitude blocking in the right location to lock the colder pattern in place.

The GFS Ensemble Mean maintains colder air along the Appalachians to the Atlantic Coast (above) with more upper troughing versus more ridging (below) on the European Model Ensemble Mean.

The GFS Ensemble Mean says the 10-15+ day period will also trend colder again. Stay tuned for later updates.

Weather Headlines

*Cold and blustery, wintry air will be felt Thursday as skies become mostly sunny during the afternoon with a surge of increasingly dry low-level air.

A notable northwest to southeast temperature gradient will be present, with much colder conditions along and west to northwest of the Cumberland-Allegheny Front.

Widespread Dense Fog At Upper Elevations Into Early Thursday

Former ALERT

ALERT For Areas of Dense Fog

Due to the amount of fog developing at lower elevations I have changed the alert to be more general through tonight into Wednesday. Persistent low clouds in orographic upslope flow will continue to produce dense fog at high elevations into early hours of Thursday.

*Rain with a chance of thunderstorms spreads back across the mountain area Tuesday into Wednesday-Thursday (January 14-16).

Heaviest rain totals are expected to extend from the Cumberland Mountains south across the Tennessee Valley and southern Appalachians. Those living and driving along streams and in low-lying, flood prone locations will need to be alert for ponding and water level rises given saturated ground and recent rains.

*Colder air pushes into the mountains Thursday into Friday morning. The coldest air will be in lower levels of the atmosphere with an inversion aloft. The coldest low level air will be felt in locations along and north of the Tennessee Valley Divide and High Knob Massif.

Short-Term Forecast

Overnight Into Monday Morning

High clouds. Large vertical temperature spread between sheltered mountain valleys and gusty middle to upper elevation mountain ridges. Winds WSW-WNW 5-20 mph, with higher gusts, on mid-upper elevation ridges. MIN temperatures varying from 28 to 34 degrees in colder valleys to the mid 40s to low 50s. Wind chills in the 30s along upper elevation mountain ridges.

Mountain valleys decoupled from boundary layer winds, especially at lower-middle elevations, will be much colder than exposed mid-upper elevation ridges which will hold in the middle 40s to lower 50s.

Monday Afternoon

High clouds. Unseasonably mild with temperatures varying from upper 40s to the middle-upper 50s. Winds SE to S at generally less than 10 mph below 2700 feet. Winds S-SW at 5-15 mph, with higher gusts, at upper elevations.

Monday Night Into Tuesday Morning

Increasing and lowering clouds with rain developing toward morning. A chance of thunderstorms. Windy across mountain ridges and exposed plateaus. Winds SSE-SSW at 5-15 mph and gusty below 2500 feet. SSW-SW winds 15-25 mph, with higher gusts, on mountain ridges above 2700-3000 feet. Unseasonably mild with temps in the upper 40s to middle 50s, except colder in sheltered valleys into the evening prior to rises. Cloud bases lowering to obscure high mountain ridges into Tuesday morning.

Isentropic upglide with increasing warm air advection will increase the coverage of rain, with the chance of elevated convection, across the southern Appalachians and Tennessee Valley into Tuesday morning. Temperatures in sheltered mountain valleys will be able to decouple initially from PBL flow, with drops into Monday evening prior to rising temperatures into the overnight with enhanced mixing and development of showers and possible elevated thunderstorms with downward momentum transfer.

Interactive Doppler Radar

Update_Tuesday Afternoon

Periods of light rain and drizzle. SW-W winds 5-15 mph, with higher gusts along mid-upper elevation mountain ridges, becoming NW-N. Dense fog (lowering cloud bases) widespread at mid-upper elevations along and north of the High Knob Massif-Tennessee Valley Divide (areas of fog at low-middle elevations elsewhere). Temperatures mainly in the upper 40s to upper 50s.

Tuesday Night Into Wednesday Morning

Low clouds. Dense fog at upper elevations, with cloud bases on middle elevations along and northward of the High Knob Massif-Tennessee Valley Divide. A chance of showers, with thunder possible into morning. Variable winds at 5-15 mph with higher gusts on mountain ridges. Temps in the 40s to lower 50s (coolest high elevations).

Wednesday Afternoon

A chance of showers and thunderstorms. SW winds 10-20 mph, with higher gusts, especially along middle to upper elevation mountain ridges-plateaus. Temps varying from the lower 50s (upper elevations) to the lower 60s, except locally warmer with downsloping into northern portions of Wise, Dickenson and Buchanan counties. Dense fog continuing at upper elevations in the High Knob Massif with orographic upslope flow (temps around 50 degrees along highest ridges with wind chills in the lower 40s).

The chance for showers, with possible local thunder, will increase into Wednesday evening and the early overnight hours of Thursday along and ahead of a cold frontal boundary that marks the beginning of cold air advection.

Wednesday Night Into Thursday Morning

Showers likely with a chance of thunderstorms, then turning colder with a chance of scattered light showers-drizzle. Dense fog at upper elevations becoming freezing fog along highest ridges by morning. Wind shifting NW at 8-18 mph with higher gusts. Sunrise temps dropping into the 30s (20s at upper elevations above 3500 feet) by mid-morning to mid-day (milder within downslope locations in the Clinch, Powell, Holston valleys).

Cold air advection will be ongoing into Thursday morning and MIN temperatures are currently expected to occur through mid-morning, with readings holding near steady (rising slightly or falling slightly) during Thursday afternoon (20s at upper elevations and 30s to around 40 degrees at lower-middle elevations along and northward of the High Knob Massif-Tennessee Valley Divide). Gusty NW winds will make conditions feel significantly colder (wintry air), especially on mountain ridges & exposed plateaus.

Low clouds may linger in NW flow upslope locations through mid-morning prior to being overwhelmed (evaporated) by increasing dry air advection, thus I have now worded my updated Thursday afternoon forecast (made Wednesday afternoon) as “becoming” mostly sunny as a wintry cold air mass is felt.

Thursday Afternoon

Becoming mostly sunny & colder. Temperatures near steady (rising slightly then falling) in the upper 30s to lower 40s in locations along and north of the High Knob Massif and Tennessee Valley Divide (20s to lower 30s at highest elevations). Milder in valleys with downsloping into the Clinch, Powell, Holston river basins. NW winds 8-18 mph with higher gusts. Wind chills in the upper 20s and 30s, except 10s to mid 20s at upper elevations.

Cold air transport will continue near the surface into early hours of Friday as warm air advection begins aloft (increasing high clouds), and on highest mountain ridges into sunrise. Turbulent mixing will oppose decoupling, but frictional terrain drag below an increasing inversion within the 850-775 MB layer should allow many valleys to decouple with developing drainage flows.

Increasing high clouds aloft will hinder OLR into the predawn-sunrise period, such that cooling conditions will not be ideal despite the advected presence of very dry (very low dewpoint) air within cold air drainage source locations of the higher mountain terrain during Thursday night into Friday AM.

Thursday Night Into Friday Morning

Mostly clear early with increasing high clouds. NW-NE winds 5-15 mph, with some higher gusts, on mid-upper elevation mountain ridges. Temperatures widespread in the 20s, except 10s possible in colder mountain valleys and on coldest mountain ridges. Wind chills in the 10s to lower 20s on mountain ridges and exposed plateaus, except single digits in gusts on coldest ridges.

**An alert for High Winds will be likely for Saturday (January 18)

Weather Headlines

Update at 10 PM Saturday (January 11)

ALERT For Strong SW-W Winds Continues Into The Overnight With Diminishing Winds By Sunday Morning

Widespread 40-50 mph wind gusts will continue into the overnight. Locally higher gusts will occur. Wind speeds are expected to decrease by the predawn-sunrise period.

Interactive AEP Power Outage Map

Strong rises are occurring on steep creeks draining the High Knob Massif and these rises will continue overnight before beginning to drop Sunday.

A general 1.50″ to 2.00″ of rainfall have caused strong rises on creeks draining the high country surrounding High Knob. Caution is advised. Another period of downpours will occur along a cold front.

Previous ALERTS

ALERT For Strong SSE-SSW Winds Late Thursday Into Friday And Late Friday Through Saturday (January 9-11)

Although recent days have already been windy, with 40-50 mph gusts common at high elevations into morning hours of January 8 (local gusts to 92 mph in the Swinging Bridge Gap on Grandfather Mountain), a more widespread and prolonged period of wind is upcoming for the mountain region.

850 MB Wind Streamlines_North America

*WIND will be a big weather factor in coming days as the pressure gradient tightens up across the eastern USA with amplification of a ridge-trough-ridge pattern.

Showers and thunderstorms, with the potential for high winds and downpours of heavy rain, will impact the mountain area Saturday evening. Remain alert to NOAA Weather Radio and your favorite media sources for possible watches or warnings.

Interactive Doppler Radar

500 MB Wind Streamlines_North America

The movement of air, commonly called wind, is a very interesting atmospheric phenomenon. You can feel and smell it (due to natural and artificial chemicals) but can not see it unless something moves or rising motion causes moisture in the air to undergo condensation.

*A potentially major outbreak of severe thunderstorms and tornadoes will impact the Deep South during Friday into Saturday (January 10-11). A squall line of strong to severe thunderstorms will approach the Appalachians from the west-southwest by later Saturday.

An increasing temperature gradient across the North America continent, between the northern Rockies and eastern USA, will drive not only wind but anomalous temperatures and warmth for deep convection.

While snow has been melting, some slick areas on roads remain at highest elevations in the High Knob Massif.

Snow will become a memory into this weekend as anomalous warmth spreads across the Appalachians.

Detailed Mountain Area Forecast

Tonight Into Thursday Morning

Mostly clear and seasonally cold. Some increasing high clouds toward morning. Increasingly large vertical temp spread between frosty valleys and milder ridges. Calm valley winds with breezy-gusty W-NW winds 5-15 mph, with higher gusts on mountain ridges-exposed plateaus, decreasing overnight. Minimum temperatures varying from 10s in colder valleys at upper elevations to the 20s, except rising through the 30s on exposed middle-upper elevation mountain ridges (following initial drops).

A change from neutral to warm advection (as visually indicated aloft by increasing high altitude clouds) will allow temperatures on exposed mountain ridges to rise toward the morning hours of Thursday despite a temporary weakening of the pressure gradient.

Thursday Afternoon

Thickening high clouds. Becoming windy. SSE-S winds increasing to 10-25 mph, with higher gusts, below 2700 feet. S-SW winds increasing to 15-30 mph, with higher gusts, above 2700 feet. Max temperatures varying from 40s at upper elevations to the low-middle 50s. Wind chill factors in the 30s to lower 40s, except locally colder in gusts on highest peaks.

Warm advection increases aloft Thursday and the thickening of high clouds at this low sun angle time of year will be a factor to monitor regarding afternoon air temperatures. Ideally, they would be cooler than given above but I have allowed for downslope compression and warming leeward of the windward slopes and mountain barriers to offset the cooling due to decreased insolation through thickening clouds. High, thin clouds contribute more to the natural Greenhouse Effect and tend not to hinder warming until their optical thickness increases as forecast by high resolution models for Thursday afternoon within the 475-225 MB layer of the troposphere. Upslope locations, by contrast, in the High Knob Massif will remain chilly with increasing wind chills combining with decreasing insolation.

Thursday Night Into Friday Morning

High clouds. Windy. SSE-S winds 15-30 mph, with higher gusts, on mountain ridges and exposed plateaus below 2700 feet. S-SSW winds 25-40 mph, with higher gusts, on mountain ridges above 2700-3000 feet. Temperatures in the 30s and 40s, except locally colder in the most highly sheltered valleys (where air temps may fall toward freezing or below then quickly rise with mixing).

If the gradient increases enough by early evening it will hinder PBL decoupling of valleys, with the ones I am allowing for possible, not certain, initial drops being those embedded within the Russell Fork-Levisa Fork basins where lower elevations beneath the Tennessee Valley Divide tend to be more sheltered than valleys embedded within dissected terrain at upper elevations (where the gradient will be stronger and decoupling less likely to nearly impossible due to strong turbulent mixing). This scenario can be applied to other complex terrain locations across the Mountain Empire, but tends to be more widespread in terrain along and just northwest of the Cumberland-Allegheny Front due to its geomorphology.

Friday Morning-Early Hours Of Sunday

While showers will become possible by later Friday and Friday night (likely along eastern slopes of Blue Ridge by earlier Friday), rain with a chance of thunderstorms will become most likely by later Saturday into early hours of Sunday along the western slopes of the Appalachians. A squall line of strong-severe thunderstorms will approach from the west-southwest and will need to be monitored.

Strong pressure gradient winds will be complicated by local mountain wave winds in favored breaking zones along the northwest-north sides of the major mountain barriers (e.g., Powell Valley and Pine Mountain of Wise County to the Clinch River Valley of Russell-Tazewell counties into the leeward zones of eastern Tennessee.

Second Storm Brings Heavy Rainfall Potential

A second storm system will spread rain back across the mountains by later Monday into Tuesday, with a heavy rainfall potential.

Much Colder Pattern In Extended Range

A much colder pattern returns during the week of January 19-25, with potential for conditions to turn extreme in opposition to current anomalous warmth.

Weather Headlines

ALERT For A Messy System Tuesday Morning With Varied Impacts From South To North Across the Mountain Area.

4:30 AM Update: Freezing rain and sleet at Clintwood 1 W changed to heavy snow with 30 degrees as of 4:30 AM.

Very large, silver-dollar size flakes indicate a isothermal profile is developing and a heavy snow band is trying to form, but some sleet is mixing in as well in Clintwood.

A combination of heavy snow and sleet is falling on High Knob, with 30 degrees at the summit levels of Eagle Knob and adjacent Black Mountain. In between 4000 and 1600 feet air temperatures are 34 degrees in Wise at 4:30 AM.

Accumulating snow will be most likely along and north of a Hazard, KY to Hurley, VA line with 2″ to 4″ within the main snow band (locally higher amounts possible).

A dusting to 2″ will be likely south of this line to the High Knob Massif & Tennessee Valley Divide. Heavier amounts, up to 3″ or more, will be possible in upper elevations of the High Knob Massif.

The above is the best forecast currently possible given a high amount of uncertainty in an evolving system.

Updated Discussion

A problematic forecast period is upcoming into Tuesday morning as a fast developing and moving system will be crossing the Appalachians.

For locations along a Pikeville, KY to Elkins, WV line the forecast is relatively easy: Snow. For locations southeast of a Pikeville to Hazard line in eastern KY the forecast has become problematic with warmer air trying to nose into the system around 5,000 feet. Yet, current temperatures are colder than models predict.

Models have trended downward for locations around Norton-Wise, with amounts varying from 0.2″ to 1.4″ in the latest runs as the bulk of precipitation is now being forecast to fall as a cold rain or rain-snow mixture.

The general model trend has been for a northward shift (NW to NE) in the axis of heaviest snowfall.

A notable problem is that current temperatures are colder than models predict and low-level air remains dry with substantial evaporative cooling potential.

This increases concern that models are not fully resolving the cooling potential, such that snowfall amounts could end up higher than indicated now, especially at upper elevations above 3000 feet.

Previous Discussion

*Accumulating snow will be possible Tuesday with a passing upper air disturbance and cold air aloft. The greatest amounts are likely at middle-upper elevations as well as beneath the axis of heaviest snowfall.

While most of the snow accumulation occurred at upper elevations into January 5, a more widespread coverage is expected Tuesday with a combination of early morning onset, more moisture & moderate-heavy snowfall rates.

Extended Forecast Period

*A persistent SW upper air flow is forecast to develop during the January 9-15 period with a heavy to excessive rainfall potential across the lower Ohio Valley, Tennessee Valley and southern-central Appalachians.

An atmospheric river type of setting, anchored by high pressure centers over the eastern Pacific and western Atlantic oceans, is expected to transport Pacific Ocean and Gulf of Mexico moisture across the region with a heavy to excessive rainfall potential.

This heavy rainfall setting will be supported by anomalous January warmth and humidity, with embedded convective rainfall acting to complicate the setting to enhance the flood and flash flood potential.

ALERT For Convective Snow Bursts With Accumulating Snow Through The Evening (January 4) Along With Snow Showers And Flurries

Local bursts of heavy snow, with snow squalls, will continue into the evening. Rapid drops in visibility will occur in wind driven snow to create hazardous conditions for travelers.

Slick conditions will develop on roadways in areas impacted through this evening into the overnight hours of Sunday (January 5). The greatest general coverage will be in W-NW-N flow upslope locations.

New Year And Decade_Weather Headlines

*The first significant storm of 2020 will begin impacting the mountain region Thursday into Friday (January 2-3).

A deep trough developing over the eastern USA will transport Gulf of Mexico moisture across the region with a heavy rain potential along and just west of the Appalachians.

*Heavy rainfall amounts with the potential for strong rises on streams is being monitored for late Friday into early Saturday (January 3-4).

The 51-member European Ensemble group is predicting amounts varying between 1.00″ and 3.00″ at the Wise gridpoint, such that the axis of heaviest rainfall is yet to be determined. It is most likely to be located over the Tennessee Valley and western slopes-foothills of the Appalachians given a westerly component to flow streamlines.

*Much colder air with rain showers changing to snow showers is expected Saturday afternoon into Saturday evening. Initial cold air transport on SW flow will shift NW with snow showers and possible squalls Saturday night into early Sunday (January 4-5).

Stay tuned for better resolved snowfall amounts and positioning as the event comes into view of high-resolution terrain models.

*A cross-barrier jet is expected to generate high winds along the Blue Ridge during Saturday night into Sunday (January 4-5).

*Milder conditions are expected January 6-7 as flow shifts southerly in advance of a second system.

*A second disturbance in NW flow aloft is being watched for more rain and snow during the January 7-8 period.

*A milder than average pattern is currently being indicated for the January 9-14 period.

Hemispheric Flow Pattern_No Winter Lock-down Seen Yet For Eastern USA

A review of the 2019 upper air flow regime finds persistent troughing across the western-central portion of the USA, keeping the Mountain Empire and Appalachians within a relatively mild, wet pattern (with above average total precipitation but below to much below average snowfall).

The year of 2019 will end having produced the least snowfall of the past 26 years at upper elevations in the High Knob Massif, with amounts only around 37% of the longer-term average.

A southerly to easterly anomaly to the flow pattern within the surface to 500 MB sector contributed to anomalous wetness during 2019 (and previously during 2018).

It is not surprising that this pattern wants to repeat, and that is what models are showing as the general flow pattern into mid-January.

The Winter Season Of 2019-20

Despite many factors favorable for persistent winter, that has not yet materialized as the polar vortex has become strong and hemispheric flow has featured limited blocking since the beginning of Meteorological Winter and a stronger zonal than meridional component to the flow field (below).

In other words, the polar jet stream has not been highly amplified and southward dips have been transitory, progressive and short-lived.

Although not at record strength, the zonal mean zonal wind flow has been stronger than average (in the 70-90% percentile) following a notable weakening in early December (above).

Temperatures have fallen to record cold levels within the stratospheric polar vortex (above), in the 50-90 degree North zone, indicating that the vortex has been stronger than average.

Although seemingly not intuitive, a strong polar vortex favors warmer than average conditions across middle-latitude continents as it promotes more zonal (west to east) than meridional (north to south) flow across the hemisphere.

A recent upward trend in temperatures above the North Pole, toward the long-term average (gray line above), appears to be associated with a reflective disturbance that will allow for some amplification of the polar jet stream into the eastern USA in the coming week, however, this will be progressive in nature and a setting which is favorable for cross-polar flow will not develop to help lock winter into the region.

The MJO is also working against USA winter, with a forecast movement into phases 4-6 which are mild phases for the USA during winter.

This certainly does not mean that no snow and cold air will occur, but for those looking for the development of a prolonged, persistent wintry pattern it is not favorable in the short-term.

These are reasons for a revision of the Climate Prediction Center forecast for January 2020, which predicts wetter & milder than average conditions across much of the southeast USA.

There are some signs of changes beyond mid-January, but those are merely trends to be followed (like analogs of past patterns).

Why may the use of analogs be less effective today? Could this be due to the forcing response of a atmosphere that is different from recent decades in terms of its chemistry and water vapor (sensible-latent heat) content?

Weather Headlines

Reference History Of Christmases Past

*A nasty pre-Christmas storm system will pass mainly south of the Cumberland Mountains

*Unseasonably mild weather conditions will dominate the Christmas Holiday period

*A transition back to a colder, wintry pattern will occur as the new year arrives by January 2020

NASTY Pre-Christmas Storm

Although this storm has been very well predicted in the modeling, the northern extent of the precipitation shield has been highly variable in the modeling.

With that noted, a review of more than 100 models of the most recent runs (includes ensemble members) places the northern extent somewhere between the Kentucky-Virginia and Tennessee-North Carolina statelines. Rain amounts within the southern Appalachians will be greatest in southwestern North Carolina.

Interactive Doppler Radar

While a few wet snowflakes can not be ruled out for crestlines of the Smokies, Great Balsams and Black mountains, it will mostly be a cold rain as the main pocket of cold air passes farther south. Wind driven rainfall and low clouds engulfing the high country of these southern mountain ranges will be the greatest impacts for those traveling, hiking, and hunting from Sunday through Monday (22-23 December 2019).

The greatest flood threat will be across the low country of the Deep South, especially the Georgia and Carolinas. Strong rises along streams draining the eastern slopes of the southern Appalachians will be possible.

National Weather Service Watches-Warnings-Advisories

The European Model, which has consistently been farther north, brings light rain as far north as Breaks Interstate Park on the Virginia-Kentucky stateline.

Clearly, heaviest rainfall (as always anticipated) will impact a large corridor from parts of Mississippi east across Alabama, Georgia, the Carolinas and Florida.

Unseasonably Mild Christmas Pattern

A broad region of upper-level ridging will generate unseasonably warm conditions during the period between Christmas and New Year’s.

Most of the continental USA will have unseasonably mild-warm conditions during this upcoming forecast period.

Pattern Change By Early January 2020

A change back into a colder, wintry pattern is currently expected as the new year begins. This also has support from past analog years featuring an analogous pattern to that of Christmas Day 2019.

Although the hemisphere pattern this year is very similar to the analogs, local conditions with respect to snow cover was certainly not identical with variations highlighted in the History Of Christmases Past section.

One would certainly be hard pressed to find a more similar upper air match across the Northern Hemisphere to that featured between analog years (above) and the forecast for this year (below) on Christmas Day.

Although every pattern and year is different, this does spark interest in seeing what came next in the analog years for their winter seasons.

Winter seasons with a Christmas Day pattern most similar to 2019 featured high-latitude blocking as a dominate circulation mode, associated with negative phases of the Arctic and North Atlantic Oscillations.

The repetitive appearance of high-latitude blocks near Greenland and in the Gulf of Alaska have already been observed this season, driven by warm sea surface temperature anomalies and other factors.

To have these blocks reappear in similar locations during coming weeks would not be surprising and has been an expected trend already highlighted in the major features to watch for Winter 2019-20.

Previous Discussion

The potential for a nasty storm system to impact the Mountain Empire is increasing for late this weekend into early next week, with more and more models beginning to follow the early trend of the GEM (Canadian) Model and JMA (Japanese) Model, and some ensembles, that have displayed a more northward track.

The Canadian and Japanese models, and many of their ensemble members, have been consistent in bringing the precipitation shield with this southern stream storm far enough north to impact much of the Mountain Empire.

While the GFS Model and its ensembles have consistently kept the precipitation shield well to the south, the NAM Model and European have recently come into better agreement with the Canadian and Japanese models.

While impacts are likely to be greatest toward the south, versus the north, with a sharp gradient and cut-off on precipitation amounts to the west and north, exact impacts remain to be worked out for given locations.

It is important to realize that 100-200 air miles is large from the perspective of a given point, but for global-scale models such as the European, GFS, Japanese (as examples) this is only a small difference.

Past climatology of similar systems suggests that the precipitation shield will likely reach northward to the mountains of southwestern Virginia and far southeast Kentucky where orographic gravity waves (mountain waves) become prolific and weather systems “feel” the underlying topography (as exemplified by the famous Mountain Empire of the southern Appalachians).

While a cold rain will be the primary mode for most, the potential for wet snow can not be ruled out for highest elevations in the southern Appalachians (e.g., Mount Mitchell and backbone of the Great Smokies).

Stay tuned for later updates.

Previous Statements

Caution For Low Temperatures And Wind Chills Into Thursday Morning

Temperatures in the 10s and low 20s will combine with breezy to gusty NW-N winds to generate bitter conditions into Thursday morning across exposed mountain ridges and plateaus. Cooling in valleys will accelerate toward morning as drainage of cold air increases.

Mountain valleys are “milder” than exposed ridges and plateaus this evening, with less wind to generate chill factors, but cold air drainage will increase overnight into morning as winds decrease and clouds diminish.

Wind chills in the 10s on exposed middle elevation ridges and plateaus, with single digits at upper elevations (sub-zero chills in gusts on highest peaks), will continue into the overnight before winds diminish in the predawn.

Rain will change to light snow and snow showers into Tuesday afternoon and evening. Accumulations from a dusting up to 1″ will be possible below 2500-3000 feet, with 1″ to 2″ in upper elevations above 3000 feet (*).

*A burst of snow will be possible in upslope locations along-north of the High Knob Massif and Tennessee Valley Divide between sunset and midnight with the approach of a upper wave and the initial low-level 850 MB thermal minimum on NW-N upslope flow.

Slick conditions will develop on roads at upper elevations with persistent snow and snow showers.

The development of slick conditions will also be possible on middle-lower elevation roadways (especially secondary routes) after sunset within locations receiving more persistent snow showers (upslope locations) and a possible burst of heavier snow between sunset and midnight Tuesday.

Rime formation is expected at elevations above 3000 to 3300 feet, depending upon the exposure, during Tuesday afternoon into Tuesday night with orographic clouds obscuring the high country in sub-freezing air.

Temperatures Will Continue To Drop Into Wednesday Morning.

Air temperatures will drop into the 20s Tuesday night into Wednesday morning, with 10s at highest elevations. Wind chill factors will range in the 10s to near 20 degrees, except for single digits at upper elevations (locally below zero on highest peaks).

Caution Advised Around Whitewater Creeks Draining The High Knob Massif

High stream levels and swift water on creeks draining the High Knob Massif will continue through tonight into Wednesday, (18 December) following a general 1.50″ to 2.00″ of rainfall.

Former Alerts

ALERT For The Potential Of Flash Flooding And Flooding Late Monday Into Tuesday

A general 0.50″ to 1.00″ of rain fell overnight into Monday morning, from the High Knob Massif northward to Clintwood and Breaks Interstate Park, with embedded thunderstorms. Additional rain, with possible downpours, will become likely Monday night into the overnight-predawn hours of Tuesday.

Interactive Doppler Radar

*The latest HRRR (High Resolution Rapid Refresh) model is showing the potential for 1.00″ to 2.00″ rain amounts into Tuesday morning and is attempting to resolve the orographic component. Models struggle to handle both convection and orographics.

850 MB Streamline Flow Field

Atmospheric conditions over the mountains are more stable than locations to the west and southwest of the Appalachians, but there is a notable orographic component on moderate-strong SSW-WSW flow streaming from the Gulf of Mexico (sea level) upward into the Cumberland Overthrust Block and High Knob Landform.

Residents living or driving along streams or into low-lying, typically flood prone locations should remain alert for changing conditions through tonight into early Tuesday.

Water gushing out of the High Knob Massif in wake of recent rainfall and snow-rime melt is expected to continue through Tuesday, with potential for significant rises in water levels if additional downpours develop into Tuesday.

Strong SW Winds Monday Night Into Tuesday AM Will Shift NW With A Plunge In Temperatures And Wind Chills During Mid-Morning Into Tuesday PM

Update: 3:00 PM Monday_16 December 2019

Wind speeds will increase again Monday Night into Tuesday as a strong cold front approaches and pushes across the mountains. A wind shift from SW to NW is expected between 7-10 AM Tuesday, with a sharp temp drop through mid-morning into Tuesday afternoon.

Former Discussion & Updates

*ALERT For Strong S To SW Winds Developing Monday Into Tuesday AM

*Strong S-SW winds will develop late tonight into Monday morning as a low-level jet streak develops and surges up along the Appalachians with a strengthening pressure gradient in advance of a major storm system.

While wind gusts of 30-40 mph will become common, gusts of 50-60+ mph will be possible, especially at the highest elevations, during the predawn to post-sunrise period of Monday.

Sheltered valleys which decouple this evening from boundary layer flow will initially have calm conditions prior to recoupling with turbulence and mountain waves that will mix out the nocturnal inversion to generate rapid short-period rises in temperature (**).

Update: 3:00 PM Monday_16 December 2019

A 14 degree temperature rise occurred between 12:10 AM and 1:20 AM [19 degree (F) total change to 3:40 AM] as the nocturnal temperature inversion was dissipated by the onset of turbulent mixing and strong SW winds. Peak wind gusts reached 40 to 50 mph during the predawn in the Wise to Pound-Clintwood area.

**I have named this the Appalachian-chinook effect, where a large vertical temperature gradient develops between mountain valleys and exposed ridges and plateaus with development of strong nocturnal temperature inversions and decoupling of boundary layer flow. Turbulent flow then develops with rapid temperature rises over short-time periods as the inversion (typically nocturnal) is mixed out by turbulence.

Update: 3:00 PM Monday_16 December 2019

Stream levels are already elevated from recent rainfall and snow melt, with whitewater creeks draining the High Knob Massif gushing during Saturday (14 December).

A heavy to excessive rainfall potential will exist with the next major storm system, with southward trends in the placement of axes of heaviest rainfall on models during the past 24 to 48 hours.

Counties along the Virginia-Kentucky border are coming into a higher risk with this southward trend that will be complicated by orographically forced lift as well potential for convection to enhance rainfall amounts upon already wet surfaces.

Around 33% of the European Model ensemble group now includes VA-KY border counties in the band of heaviest rainfall amounts versus no members prior to 24-hours ago.

Stay tuned for updates.

Update: Christmas Bird Count 2019

Reference Early Winter_High Knob Massif for more scenes.

Around 50 bird species were identified during another year with bad weather conditions. A light mixture of sleet and snowflakes at the summit level of High Knob gave way to rime formation around mid-day (as the air temp dropped below freezing).

A burst of moderate-heavy, wind driven snow developed around 2:30 PM Saturday (14 December), and although accumulations were generally 0.5″ or less it added insult to already nasty conditions (orographic clouds and wind chills in the 10s).

Weather Headlines

ALERT For Zones Of Freezing Rain During The Predawn To Post-Sunrise Period Of Early Friday (13 December)

Update At 3:00 AM_Friday_13 December 2019

Freezing rain is falling at Clintwood 1 W with 32 degrees. The temperature has risen from a late Thursday evening minimum of 28 degrees. Please use extreme caution if walking on porches, sidewalks or traveling overnight into early Friday for freezing rain in valleys such as those along streams like Georges Fork Creek, Pound River, McClure River, Cranes Nest River, Russell Fork River and Fryingpan Creek (to note a few) within Dickenson County, and similar sections in dissected terrain of Wise County and Buchanan County.

*While widespread freezing rain is expected along and east of the Eastern Continental Divide, there will also be zones of freezing rain within the complex mountain terrain along the Cumberland-Allegheny Front, especially in valleys sheltered from SSE-SSW winds. These valleys are ones which still have snow cover along slopes this afternoon (12 December).

The potential exists for freezing rain, at least briefly, on adiabatic upslope cooling along the High Knob Massif early Friday (mainly above 3000-3300 feet).

Additional areas of freezing rain will also be possible for a period early Friday in other locations that will not be under an official Winter Weather Advisory.

Be certain to check your local conditions before traveling!

Mesoscale Discussion For Forecasters

Due to this being a predawn-early morning event, centered around the AM commute, it would be best if the entire area was placed under an Advisory For Freezing Rain (which I am unofficially doing with the above alert). Counties west of the Eastern Continental Divide could then be dropped from longer-lived advisories currently in effect for eastern zones.

Thursday evening temperatures will be able to drop to and below freezing in many mountain valleys with dry low-level air in place. This cooling will be enhanced by snow cover that continues along slopes within the locations of greatest concern. There is also concern that this evaporative cooling could have more widespread effects, with exposed middle elevation plateaus-ridges west of the Eastern Continental Divide being least likely to have freezing rain. (A low-level inversion is currently in place due to snow cover, with the Thursday PM max reaching 38.8 degrees at the official NWS Cooperative station in Clintwood to contrast with middle 40s at exposed middle elevation sites in Norton-Wise).

**Temperatures Thursday afternoon have been much cooler, for example, at the City of Norton Water Plant versus the Norton Elementary School Weatherbug site, exemplifying the nature of complex terrain variations that models simply can not handle but forecasters must understand and take into account.

Cloud bases will not lower until after midnight. As precip begins, with isentropic upglide driven by positive theta-e advection, evaporative cooling will develop an inversion layer at low-levels that could keep warming winds from mixing downward into the low-level freezing air.

While this will be most widespread along and east of the Eastern Continent Divide, of course, with more classic cold air damming, it will also develop locally within the complex terrain along the western Appalachians where a downslope component of air flow will develop and initially blow across the top of these local inversions until vertical mixing from orographic waves and general atmospheric turbulence can enhance mixing to valley floors. By then, however, most of this initial precipitation driven by isentropic upglide on theta-e advection may be over, helping aid mixing with downslope induced breaks for a time during Friday.

Two Significant Storm Systems In Five Days

The first of two storm systems brings the freezing rain threat early Friday, then a wave of rainfall into Saturday. Rainfall amounts will act to keep water levels elevated. Although flooding is not currently expected, some high water issues can not yet be ruled out given so much recent wetness.

Big Cherry Lake Dam is now overflowing its spillway so future water level rises along the South Fork of Powell River will be more significant for locations downstream in Crackers Neck, East Stone Gap into Big Stone Gap.

Whitewater creeks draining the High Knob Massif are already elevated. There is increasing concern for high water issues, especially into early next week when heavy precipitation amounts are likely, such that the entire mountain area will be at risk.

An influx of colder air Saturday will help to slow run-off and may cause a change to snow. Some accumulation will be possible at upper elevations. Stay tuned for later updates regarding snow levels.

A second storm system follows quickly, with a trough of low pressure already over the area by early Monday. Copious moisture transport from the Gulf of Mexico will threaten the mountain area with heavy to excessive rainfall amounts. A flood potential will exist and must be closely monitored.

While some frozen precipitation may also be a concern, initially the main focus at this point will be on the potential for high water issues early next week during Monday into early Tuesday.

The Bottom Line

*Freezing rain will be widespread along and east of the Eastern Continental Divide Friday with moderate to significant icing developing in a hybrid classic / in-situ cold air damming setting as the anchoring high pressure retreats over time (not anchored).

*Freezing rain will be possible during the predawn-early morning hours of Friday in locations along the western Appalachians, with most favored locations being mountain valleys (beneath a inversion enhanced by evaporative cooling) and upslope locations in the High Knob Massif (on adiabatic upslope cooling). Middle elevation ridges and plateaus, exposed to mixing on SSE to SSW winds, will be least likely to have freezing rain. Everyone must check their local conditions before walking or traveling outside!

The 6:15 PM air temperature is 31 degrees (12 December 2019) at the official National Weather Service Cooperative Station in Clintwood to indicate that mountain valleys in complex terrain will be colder than models predict.

Locations such as Clinchco, Haysi, McClure, Nora, Birchleaf, Coeburn, Darwin, and many others, will have temps drop below freezing prior to precipitation onset.

*Rain will elevate stream levels into Saturday and although flooding is not currently expected, some local high water issues can not be ruled out.

*A possible transition to snow is being monitored Saturday, with sticking at this time appearing to be most favored at upper elevations.

**A major storm system early next week is now expected to bring significant precipitation with the potential of flood and flash flood threats. Some wintry types will also be possible. Stay tuned for updates.