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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.