Caution for the redevelopment of slick roads tonight into early Saturday. Otherwise, snow covered secondary roads continue to be an issue for travel at highest elevations and in some local middle-lower elevation sites.

Light snow, flurries, and heavier snow showers will continue into tonight and Saturday along the upslope side of the mountains with respect to northerly (NW-NE) air flow trajectories amid lingering low-level moisture.

Cold air advection will be strongest below 850 MB, helping to establish a low-level temperature inversion into tonight and Saturday. Rime forming low clouds at upper elevations may drop into the middle elevation zone (below 3000 feet) in windward locations upstream of the High Knob Massif-Tennessee Valley Divide (Cumberland Front).

Please be cautious of enhanced slickness if fog forms in your location tonight (with air temperatures well below freezing).

Raw, cold conditions will continue through much of Saturday with hopes for eventual weakening of the inversion to allow for some sunshine. This will be a struggle, with temperatures remaining below freezing throughout most (all if no sunshine develops) of Saturday in Norton-Wise and the 10s to around 20 degrees at highest elevations in the High Knob Massif.

Additional accumulations will vary from less than 1″ to locally 2″ in favored upslope locations of the High Knob Massif, where current snow depths vary from 3″ to 6″ at elevations below 3300 feet to 6″ to 12″+ in the highest elevations (above 3300 feet). Lingering “old” snow of recent days added to depth at highest elevations.

A general 3″ to 5″ of snow fell across central-southern Wise County into portions of Lee and Scott counties by mid-day Friday, with lesser 1″ to 2″ amounts across northern Wise and Dickenson-Buchanan counties.

Huge snowflakes were a characteristic of this event, especially overnight into early Friday, but even into the afternoon hours in some locations (above).

Previous Forecast & Discussion

ALERT For Snow And The Development of Hazardous Conditions Into Friday

There is higher than average uncertainty associated with this event. Although a general 1″ to 8″+ is likely, there is potential for large variability for any given location and therefore a larger potential range.

The map below shows the favored zones based upon climatology and the current mean of forecast models. Appalachian topography is, of course, the base map.

In reality, these predicted accumulation zones may very well shift on the map below. Time will soon tell. An idea of model variability can be obtained by watching the slide show of all model runs from today (7 January).

I included all model runs but those from the European Model group (50 ensembles + the operational run + the control run), given I am not allowed to show them without a license.

I think one or more mesoscale snow bands will be possible, but where they form can not really be determined with confidence in advance. This map is, therefore, generalized with a heavy terrain focus.

This map implies, as an example, that those traveling north along U.S. 23 (between Big Stone Gap and Norton) will encounter more snow as they pass from Powell Valley in Wise County through Little Stone Gap (at Powell Valley Overlook) to the northern side of the massif.

The (+) allows for both model and terrain variability that exists depending upon which model solution (or blend) verifies. Typically, no single model is ever exact.

Greatest uncertainty exists within the Great Valley where downsloping air flow trajectories will be opposed to favorable upper air dynamics, such that ultimate depths will depend upon boundary layer temperatures, precipitation type, and rates of fall.

Although rare, the Tri-Cities can occasionally receive more snow than Norton-Wise and even the summit of the High Knob Massif (very rare, but documented). When that has rarely occurred, it has been due to a southern tracking system whose precipitation shield did not fully reach into the northern mountains of the Mountain Empire.

Western North Carolina and the Tennessee-North Carolina border area (northeast to Mount Rogers) has the highest probability of reaching higher end totals based upon typical snow forecasting schemes related to the relationships between snowfall amounts and surface, 850, 700, 500 MB low tracks.

Higher end totals will also be possible in the High Knob Massif-Black Mountain corridor of far southwest Virginia given favorable air flow trajectories. Higher uncertainty here exists due to storm track, with northern portions of the map area above expected to be at the northern extent of the main precipitation shield.

Any south or north jog in storm track could change totals over northern portions of southwestern Virginia more than in other sectors of this storm system (with air temperatures cold enough for all snow, the amount of available moisture will be a critical factor here).

It should be kept in mind, as well documented during past similar events, that the evaporative cooling potential will be somewhat greater over locations along and northwest to north of the Cumberland Front (High Knob Massif-Tennessee Valley Divide), given advection of lower dewpoints on NE-N trajectories.

Snow density will tend to be lower in this sector of the storm than farther south. Somewhat lower snow density can help compensate for less moisture (greater fluff factor), and if moisture is greater than expected will generate a snowfall maximum in this sector of the storm due to the combination of lower density and favorable orographics with significant rise on NE-N trajectories felt by communities such as Clintwood, Norton, and Wise (to name a few).

Additionally, any change in intensity (strength) of this system will be important given it is not expected to intensify until entering the western Atlantic.

Heavy Snowfall Potential for Friday

Snow will develop overnight into Friday morning with hazardous conditions expected from around Breaks Interstate Park south and southeast.

Updated Model Predictions from 7 January 2021 Runs:

Previous Discussion

Caution for slick conditions on roads at highest elevations within the High Knob Massif into Thursday (7 January 2021)

A general 2″ to 5″ of snow accumulated at highest elevations in the High Knob Massif. Extreme caution should be used for snow covered roads.

The solution to this dilemma may not be known until the system develops over the Mountain Empire late Thursday into early Friday.

The difference between a “big” snow and a “little” snow for Wise County, on the latest European Model run at 18z Wednesday, is less than 50 air miles (around 35-40 miles). This is literally nothing for a global-scale model.

The operational GEM (Canadian) Model has been most consistent with this system, while the GFS has been the weakest and farthest south. Wednesday trends feature increasing heavy snow potential being predicted by the Short Range Ensembles, NAM group, and the German Model (ICON). The GEM has predicted heavy snow across southwestern Virginia for days now.

While the operational European Model has been wobbling, and recently edged just a bit south, at least 14 ensembles of its group continue to predict heavy snow over southwestern Virginia. The European Ensemble Control has been consistent in keeping heavy snow over far southwestern Virginia.

To illustrate how models are struggling, the 00z NAM group coming in tonight is to the south and appears to be suffering from some feedback issues.

A problem being that this system is being taken across the highest mountain chain in the eastern USA, such that models are all trying to figure out how to handle this process across both space and time.

Much like an individual thunderstorm, a storm system in the atmosphere does not move from Point A to Point B, but instead it redevelopments at each point across space and time. In this case, a major problem is the redevelopment to the lee of the mountain chain.

Bitter Cold By Mid-Late January

There are signs that a major (big-time) eastern USA winter storm could develop toward the middle of January (one of numerous upper air waves within the flow field).

Getting a major winter storm requires specific conditions, such that only time will tell if these can align in such a way to support a big-time winter storm.

This would occur as cross-polar flow develops across the Northern Hemisphere.

Ensemble Model Means are beginning to reveal impacts of the major Sudden Stratospheric Warming (SSW) that is ongoing, with development of cross-polar flow expected by mid-late January.

This cross-polar flow pattern will open the door for bitterly cold, arctic air to invade the USA.

The full potential of this would be best realized, of course, above snow cover.

Reference My 27 December 2020 Discussion for more information about the ongoing major warming in the stratosphere that will continue to help change North American weather during January 2021.

Weather Headlines

1). A chance for light rain and mixed precipitation Sunday will become light snow by late Sunday into Monday. Any snow accumulations are expected to be light, mainly at upper elevations above 3000 feet (during 3-4 January).

Air is expected to turn colder Sunday into early Monday on W-NW flow (with minimal Great Lake connection).

Mixed rain and snow showers at lower elevations have been sticking at upper elevations, with some slick areas developing on northern slopes and crests. More widespread sticking will be possible around and after sunset across upper elevations (above 3000 feet). Limited sticking is expected at elevations below 3000 feet.

Caution is advised for those visiting High Knob Lookout and driving at high elevations.

2). Great Lake connected NW Flow snow will be likely Tuesday into early Wednesday (5-6 January 2021).

Snow accumulations of 1″ to 4″, with locally higher amounts, are expected in upslope flow along and NW of the Cumberland Front and along the windward side of the TN-NC border. Generally less than 1″ is expected in downslope areas.

A secondary surge of cold air will move southeast, with developing Great Lake connected NW flow, during Tuesday into Wednesday.

3). A snowstorm potential is being monitored for late this week (8-10 January period). More than one wave of significant snow will be possible.

Upper level waves (energy) moving through the jet stream flow are being monitored for amplification (intensification) as blocking strengthens across Greenland and southeastern Canada.

History Of Christmases Past
(1964-2019)

Reference White Christmas 2020 for a recap of the Christmas Holiday storm.

Winter Returns In January 2021

Important changes related to what appears to be a split in the stratospheric Polar Vortex upcoming during early January is now expected to alter the flow pattern across the Northern Hemisphere. Initially, these changes will favor warming across eastern North America and cooling across western North America.

The split on the European begins in the upper Stratosphere and works downward over time.

This update is being written on 30 December 2020.

A major Sudden Stratospheric Warming (SSW) event is now timed for the 6-7 January 2021 period.

Although produced from a UK (United Kingdom in western Europe) perspective, this video is excellent in its description of the Polar Vortex, its formation and break-down, and occasional major events known as Sudden Stratospheric Warmings.

Technically, a SSW requires reversal of winds at 60 degrees North latitude and 10 MB from westerly to easterly in direction (note this 10 day forecast).

A mild opening to January 2021 will begin to change during the 7-14 January period, with significant changes likely by mid-late month.

Strong warming will occur above high latitudes, and the North Pole, during the first week of January 2021 to result in a major SSW event.

This has also been highlighted by Dr. Judah Cohen in his weekly AO/PV Blog.

The current best analog pattern to what is being predicted is found during Winter 2009-10 (above).

While no two events, or seasons, are exactly the same it would be foolish not to recognize these correlations moving forward.

Major stratospheric warming events represent some of the most dramatic short-period (sudden) changes in the climate system, and occur within a typically stable setting (the stratosphere).

Impacts tend to propagate downward over time (after having been forced by wave activity propagating up from the troposphere) as coupling occurs.

It is also interesting to note, the SSW Event of January 1985 occurred during a weak La Nina winter with a E-W QBO (Quasi-biennial Oscillation) pattern.

While changes may begin to be seen toward the 5-10 January period, it will likely be mid-late January before full impacts are felt.

Given the difficulty in forecasting tropospheric weather conditions 24-48 hours away during winter, you may wonder why I would show a 16-day forecast chart? It just so happens, that once changes begin the enhanced stability (typically) of the stratosphere makes forecasts at least a little more dependable.

Getting to this point of a Major SSW can, indeed, be difficult for models to handle, but the confidence in this future stratospheric setting is now much greater than are details of how this event will actually impact local weather conditions within the troposphere (e.g., in the Mountain Empire).

What those impacts will be, in terms of details and intensity, remain to be resolved, but a major SSW climatologically tends to enhance the potential for severe winter conditions across middle latitudes.

Bitterly cold air and expansion of a deep snowpack has generated what may be a New Global Record for high barometric pressure, in Mongolia, related to persistent blocking in the region of the Ural Mountains and upward wave activity flux (WAF).

The Bottom Line…Despite a mild start, January 2021 is likely to generate dramatic weather changes as the hemispheric flow pattern across North America is changed by major stratospheric warming.

ALERT For Hazardous Conditions Developing Monday Night Through Mid-Morning Tuesday

Developing NW flow in combination with a pocket of very cold air aloft will generate snow, snow showers and locally intense snow squalls during Monday night into Tuesday.

Snowfall Forecast

(30 November-1 December 2020)

2″ to 4″ below 3000 feet

4″ to 8″ above 3000 feet

2″ or less in downslope locations

Locally higher amounts will be possible, especially at highest elevations within the High Knob Massif.

Target Snowfall: 3″-4″ in Norton-Wise (+/- 1″ error potential), which implies a 2″ to 5″ spread is possible for elevations below 3000 feet in the upslope zone north and northwest of the High Knob Massif.

Early Winter 2020_High Knob Massif

Introduction To The High Knob Massif

(Select 1080p HD for best viewing on YouTube)

High Knob Massif_Video And Introduction Details

Very cold air aloft and steep lapse rates (strong vertical drop in temperature with height) will support bursts of heavy snow (squalls).

Temperatures are predicted to drop to between -25 to -30 degrees Fahrenheit below zero at 17,000 to 18,000 feet during Monday Night into Tuesday Morning.

While most prevalent in upslope locations, some of these may also impact downslope locations into the Clinch, Powell, Holston and Great valleys with rapid sticking during periods of low visibility.

Heavy Snowfall Potential

A major change in the weather pattern across the continental USA is coming as December begins next week.

This also marks the start of Meteorological Winter, the three month period from December through February used for climate purposes to characterize the winter season.

This is a pattern that models have long been showing to various degrees, as evident by my weekly weather column written and submitted back on 23 November 2020:

It is now clear that a pattern supporting bursts of heavy snow embedded within a general field of light snow and snow showers will develop across the southern-central Appalachians later Monday into Tuesday of 30 November-1 December 2020.

Cold air aloft in combination with upsloping NW flow will generate widespread snow, snow showers and more intense snow squalls. As would be expected, heaviest snowfall amounts will be along the western side of the Appalachians.

Locations along and northwest of the Eastern Continental Divide, Tennessee Valley Divide and High Knob Massif, will feature the heaviest snowfall amounts versus downslope decreases in between and leeward of these major mountain barriers.

Note that this system is just coming within view of short-range, high-resolution models. At the present time (27 November), the upper air forecast would suggest that temperatures in the mid-10s to mid-20s will be common from the High Knob Massif north and northwest across Norton-Wise, Pound, Clintwood and nearby communities by the predawn-sunrise hours of Tuesday (1 December). Much lower wind chills will be felt across exposed mountain ridges and plateaus.

It is likely that Tuesday will feature little temperature rise, and may even have falls depending upon the exact timing of coldest air.

While too early to actually predict snowfall amounts with high confidence, preliminary analysis using past systems already documented in climatology suggests that upslope locations can expect 3″ to 6″ below 3000 feet, with 6″ to 12″+ above 3000 feet (with drifting on ridges and riming at upper elevations).

Tuesday is currently looking to be a mid-winter type of day, albeit with an early shot of “fresh” arctic air.

Extended Wintry Pattern

The Pacific Ocean will be looked at a great deal this winter season as La Nina acts as one of the major forcing factors for the 2020-21 Winter.

A positive (+) PNA pattern favors western USA ridging and eastern USA troughing in the upper air, with colder than average conditions across the Mountain Empire.

It currently appears that a wintry pattern will dominate the first half of December across the eastern USA. What happens during the always important second half of the month remains unclear from this distance.

Independence Day Holiday Period

*Mid-Summer conditions will feature warmer than average temperatures and many dry hours during the Independence Day Holiday period.

Any thunderstorm that develops during the Holiday period could become briefly and locally strong to severe, with dangerous lightning, gusty winds, and downpours of rain. Coverage is expected to generally remain low.

Chances for hit-miss showers and thunderstorms will remain low through Saturday, with somewhat better chances for afternoon and evening activity during Sunday and Monday of the Holiday period.

July Opens Amid Warmer-Drier Trend

A warmer than average temperature trend is being predicted by forecast models during the first half of July across much of the continental USA.

A trend toward somewhat cooler temperatures toward mid-July is currently being indicated, driven by a possible increase in showers & thunderstorms.

A drier than normal rainfall trend, in general, is being forecast by models during the first couple weeks of July.

Actual rainfall amounts, however, will undoubtedly vary significantly across the region (reference June).

Recap Of June 2020

It should be noted that following maps use model interpolation in between actual data collection sites, such that local conditions may be different than represented (especially in complex terrain).

June 2020 featured near to slightly below average temperatures and rainfall amounts that varied from much below average to much above average.

The coolest temperatures, relative to longer-term averages, were experienced during the day.

June Precipitation Totals

High Country (Upper Elevations)

Snowshoe Mountain (WV): 8.46″
(+3.62″)

Mount LeConte (TN): 8.28″
(+0.98″)

Big Cherry Lake Dam (VA): 7.48″
(+1.35″)

Canaan Mountain (WV): 5.91″
(+0.67″)

Beech Mountain (NC): 5.72″
(+0.70″)

Eagle Knob (VA): 5.65″

Grandfather Mountain (NC): 5.36″
(-0.95″)

Newfound Gap (TN): 5.34″

Mount Mitchell (NC): 4.95″
(-0.40″)

Black Mountain (KY): 4.76″

Boone 1 SE (NC): 4.21″
(-0.85″)

Burkes Garden (VA): 3.97″
(-0.25″)

Middle-Lower Elevations

Wytheville (VA): 7.15″
(+3.58″)

Roan Mountain 3 SW (TN): 4.10″

Grundy (VA): 3.86″
(-0.64″)

Richlands (VA): 3.52″
(-0.43″)

Wise 1 SE (VA): 3.30″
(-1.16″)

Saltville 1 N (VA): 3.08″
(-1.07″)

Clintwood 1 W (VA): 2.91″
(-1.88″)

Tri-Cities (TN): 2.75″
(-1.15″)

Lebanon (VA): 2.57″
(-2.01″)

Abingdon 3 S (VA): 2.33
(-1.73″)

Rogersville 1 NE (TN): 2.06″
(-1.75″)

ALERT For The Potential Of Heavy To Locally Excessive Rainfall Amounts

Interactive Lightning And Storm Tracking Doppler

Folks living and driving (and hiking) near streams and in low-lying, flood-prone locations will need to remain alert and closely monitor changing weather conditions through coming days.

Some Thunderstorms Could Be Strong To Locally Severe Into Sunday-Monday

Interactive 850 MB Flow Field

Observe flow field streamlines from the Atlantic Ocean across the Gulf of Mexico into the southern Appalachians in a clockwise flow around High pressure centered near Florida. In addition, there is some concern that Saharan Dust could contribute some CCI (cloud condensation nuclei) to further enhance rainfall making capability as air is lifted by a combination of dynamics and orographics through a deep vertical column.

Roles Of Mineral Dust As Cloud Condensation Nuclei

Efficiency of Dust Storm Particles As CCI

Measurement Of CCI And Droplet Activation Kinetics

The role of dust as CCI is complex, with varied results depending upon many factors, not the least of which is location and particle sizes. CCI as a linkage between different climate system components, however, is clear and more research is needed to better understand these connections and the role dust plays from weather to ecosystem biodiversity (e.g., Saharan dusting acting to fertilize the Amazonian Rainforest).

Influx of tropical moisture around High pressure toward the south will combine with a upper air setting favorable for upward vertical motion to support a heavy to excessive rainfall potential.

Interactive 500 MB Flow Field

A very moist atmosphere will combine with disturbances passing through a developing W-NW flow field to trigger clusters of showers and thunderstorms into early next week.

Some thunderstorms could be strong to severe on Sunday into Monday, with two main modes being watched for the severe potential:

1). Mesoscale Convective Systems that may develop in W-NW flow will have the potential to support strong-severe convection

2). Localized convection could turn severe, especially if breaks develop in the rainfall pattern to enhance instability associated with daytime heating.

Mesoscale, higher resolution models, are showing wide variations in rainfall with potential for locally excessive amounts and flash flooding.

The placement of heaviest rainfall amounts continue to vary among forecast models, and from run-to-run on the same model, but a clear signal for significant rain amounts is being displayed on all models.

Synoptic-Scale Weather Setting

A somewhat unusual pattern featuring heat ridge formation over the Great Lakes and southeastern Canada will cause temperatures, relative to long-term average, to skew hot in the north country to contrast with near average conditions over the SE USA and southern Appalachians.

A boundary separating seasonally hot air to the north from seasonal air toward the south will generate clusters of showers-thunderstorms.

The position and movement of the boundary over time will help to dictate where heaviest rains fall. Models are currently in disagreement.

Soil moisture has decreased significantly from the end of March in many places (especially amid high June sun angles).

Due to excessive amounts of precipitation for this point in a year, soil moisture remains on the surplus side, especially in wettest places.

High Knob Massif Precipitation Update (23 June 2020)

Black Lives Matter Statement

ALERT For Local Downpours Beneath Slow Moving (Hit-Miss) Showers And Thunderstorms

Slow moving showers and local thunderstorms will continue to produce downpours into this weekend.

Interactive Real-Time Lightning And Storm Tracker

The potential for excessive localized rainfall will continue as a upper-level low slowly dissipates.

Interactive 500 MB Flow Field Streamlines

A new upper-level low will drop into the Great Lakes and eastern USA into next week, following weekend warming with lower rain chances on Sunday.

This will continue and enhance rainfall chances next week as air temperatures trend from near to above average in early week to near and below average during mid-late next week.

An enhanced surge of deep, tropical moisture is being monitored for later in this forecast period that could support widespread heavy rainfall & storms.

Stay tuned for later updates.