Monthly Archives: January 2021

013021 Forecast

Reference Mid-Winter 2021_High Knob Massif for a recap of recent conditions, as well as a 2020 precipitation update.

Monday Evening Update: 11:00 PM (1 February 2021)

Roadways at all elevations are either snow covered or are becoming snow covered across all upslope locations within Dickenson & Wise counties.

Please use extreme caution into Tuesday.

Wind Blown Snow (15 degrees) on Eagle Knob_10:44 PM on 1 February 2021

Event snowfall totals as of 10:44 PM varied from 2.5″ in Clintwood to 11.0″ on Eagle Knob of High Knob Massif, where wind blown snow was becoming more of a factor (snow depths increased between 1″ and 4″ in the above scene during the past 4 hours).

Thanks to my friend Cody Blankenbecler, as always, for these Eagle Knob reports.

Updated at 10:00 PM on 31 January 2021

ALERT For A Prolonged NW Flow Snow Event From Monday Morning Through Wednesday AM (1-3 February 2021)

Snowfall Forecast
(Total For 1-3 February)

4″ to 8″ below 3000 feet

8″ to 12″+ above 3000 feet

4″ or less in downslope areas

Target Snowfall 8″ at 3000 feet: (+/-) 2″ Error Potential,
implying a potential for 6″ to 10″ of snow at 3000 feet in
the 3-day period during 1-3 February 2021.

Significant rime formation is also expected at upper elevations, potentially enough to droop or even break tree limbs and small trees.

Total ground depth is expected to generally be less than total snowfall due to low density snow and significant settlement over time, in combination with some melting and sublimation. The exception will be at upper elevations where areas of blowing snow and drifting are likely to cause greatly varied depths and much deeper snow in drift zones.

Residents and those traveling at high elevations should plan for the possibility of impassible roads, especially in windward facing basins and mountain ridges from Big Cherry Lake to High Knob Lake, and locally in other places within the high country above 3000-3500 feet.

Deep moisture and seasonally cold air aloft will combine to generate widespread snow during Monday into Tuesday morning. Snowfall from Tuesday AM through Wednesday AM will become more showery, and due to more shallow moisture, more restricted to windward slopes of the major orographic zones.

While forecast models and forecasters say that this event will last until Tuesday morning, the model streamline flow field trajectories predict it will persist into Wednesday morning for the orographic upslope locations along-northwest of the major mountain barriers, especially the Cumberland-Allegheny Front where shallow moisture being lifted will be most productive as actual, documented past observations illustrate.

Relationship Between NW Flow Snowfall And Topography

It would be a better forecast world if forecasters would seriously look at research already done by Baker Perry, Charles Konrad, and even myself (locally in southwestern Virginia) with respect to snowfall and topography and stop following this model bias toward the Blue Ridge given elevation is only a single factor within a complex array of factors that determine snowfall.

Forecasters Need To Follow Field Research

Although models have gotten better at showing general terrain distribution (now showing a “horseshoe” configuration around the TRI), they still often over-estimate snowfall in locations that are colored dark-grey in the above graphic from Baker Perry & Charles Konrad.

Past climatology of these flow events shows that highest total snowfall amounts tend to occur from the High Knob Massif to Snowshoe Mountain and Canaan Mountain along the Cumberland-Allegheny Front, with a secondary maximum (often less, but not always) along the Blue Ridge (which are the primary, or initial, lifters on SE flow trajectories).

This is opposed to forecast models and forecasters who persistently focus upon the Eastern Continental Divide, which is the secondary lifting zone in NW flow settings (the Great Smokies, being farthest southwest, function more as the primary lifting zone at their latitude given the lower terrain to their northwest. The main hinderance on NW Flow for the Smokies being Great Lake moisture advection is often not as abundant at their latitude versus farther northeast along the Appalachians, with abundance increasing from southwest to northeast along the mountain chain with respect to Great Lake moisture in the mean).

Every snowfall event is different, and in this case streamline predictions are for Great Lake moisture transport far to the south. I have no problem with heavy snowfall amounts being predicted for the Great Smokies. The problem, is that Winter Storm Warning snow within this type of setting is a no-brainer from the High Knob Massif to Canaan Mountain.

Highest snowfall amounts will occur along the windward mountain barriers, along and west to northwest of the Cumberland-Allegheny Front as well as along and adjacent to the Eastern Continental Divide.

Part 1: Miller B Winter Storm

With the above duly noted, no Winter Weather Advisory or Winter Storm Warning was issued for Wise County for Part 1 of this event (despite 1.5-2.5″ or locally more in Norton-Wise-Sandy Ridge, as well as Black Mountain, and 6-7″ above 3000 feet in the High Knob Massif).

If there is nausea about including the Powell River Valley, then begin breaking out northern Scott and highest elevations of Lee to go with mid-upper elevations in Wise County as a separate forecast zone from the Powell & Clinch river valleys that could form a separate (lower elevation) forecast zone.

Nothing. Nada, to follow a trend that is reverting back to pre-2008 when the MRX NWSFO would persistently group Wise County with Great Valley counties.

Heavy Snow_Eagle Knob of High Knob Massif_1:21 AM_31 January 2021

Nearly all precipitation fell as snow at upper elevations of the High Knob Massif into morning hours of 31 January, with 6″ to 7″ of snow accumulating from the Little Mountain community adjacent to Big Cherry Lake to the High Chaparral, Robinson Knob, and Moore Knob communities.

Locally greater amounts may have occurred at highest elevations, but due to severe winds and significant blowing snow-drifting it was nearly impossible to determine.

Snow Depth In High Chaparral_8:29 AM_31 January 2021

Extreme Winter Potential

The potential for extreme winter conditions is being monitored for late this weekend into next week.

GFS Model_500 MB Height Anomaly_4 PM on 7 February 2021

While model timing and intensity vary, both the European and GFS are currently predicting that bitterly cold air will move across the North Pole and plunge southward through Canada into the USA by next week.

GFS Model_850 MB Temperature Anomaly_4 PM on 7 February 2021

The coldest mass of air in the Northern Hemisphere, relative to climatological means, is being predicted to plunge into the central-eastern United States.

This is an end result of a Major Sudden Stratospheric Warming event observed during January, as have been (which can be debated if wished) the recent, current and future snowstorms impacting the region.

Review the Sudden Stratospheric Warming video by the MET Office in this section to aid understanding of how a major SSW event can trigger an arctic outbreak.

GFS Model_850 MB Temperature Forecast_1 AM on 8 February 2021

Although it remains too early to know if this will verify, there is increasing confidence in an arctic outbreak impacting portions of the United States by next week.

Stay tuned for later updates.

Previous Discussion

ALERT For A Period Of Accumulating Snow And/or Sleet-Rain Around And Following Sunset Saturday Evening (30 Jan 2021)

While virga (snow aloft) was developing above the area early Saturday afternoon, nothing more than flurries or sleet pellets will reach the surface until later this afternoon-early evening due to dry, low-level air.

A more organized band of precipitation, mainly snow or snow-sleet, will develop by around and after sunset this evening along a warm front.

Snow-Frozen Type Forecast
Part I of A Three Act Storm

Saturday Night to Sunday Morning

Accumulations are expected to vary from a dusting toward the Virginia-Tennessee border, to the southwest of the High Knob Massif, up to 3″ at highest elevations and toward the northeast of the High Knob Massif-Tennessee Valley Divide.

Locally greater amounts, more than 3″, could occur at highest elevations in the High Knob Massif if part of the next wave coming in during early hours of Sunday is snow or snow-sleet prior to changing to freezing rain-rain on strong upslope flow across cloud-engulfed upper elevations.

Although temperatures above the summit-level of the High Knob Massif will rise above freezing into Sunday, adiabatic cooling on strong upslope flow over snow cover will maintain a much colder temperature profile at ground level. This will cause the bulk of precipitation to fall in frozen form at highest elevations in the High Knob Massif, with initial snow changing to sleet and freezing rain (and just rain eventually, as upslope weakens and the flow direction shifts).

Dusting Up To 3″

A complex Miller B Winter Storm will impact the mountain region this weekend through early next week, with three distinct phases (parts).

Complex Winter Storm Impacts Mountain Region

Part 1 = Initial snow-sleet-freezing rain along a warm front (Saturday evening)

Part 2 = Transition to rain Sunday (potential for freezing rain at highest elevations in the High Knob Massif)

Part 3 = Prolonged period of NW-N Upslope Flow Snow from late Sunday Night into Tuesday afternoon or night

Significant snow accumulations along the upslope side of the mountains are expected with Part 3. My preliminary estimate, which will likely change, is 4″ to 8″+ for locations along and northwest-north-northeast of the High Knob Massif and Cumberland Front.

Appalachian Structural Front

Secondary zones with enhanced snowfall will occur along the Brumley Mountain to Burkes Garden section of Clinch Mountain, and from the Mount Rogers-Pine Mountain area southwest along the Tennessee-North Carolina border to include Mount Mitchell.

012621 Forecast

Reference Mid-Winter 2021_High Knob Massif for a recap of recent conditions, as well as a 2020 precipitation update.

ALERT For A High Impact Snow Event During Wednesday Night Into Thursday Morning (27-28 January 2021)

A High Impact event is expected due to rapid temperature drops and moderate to high snowfall rates following sunset.

NOTE this has to be considered a HIGH impact event. Travel along I-81, the busiest road, through the Great Valley will feature no snow accumulation in the Knoxville area to 6″ or more centered upon the Tennessee Valley Divide (around Mountain Empire Airport) where travel may become impossible for a period of time.

Snowfall Forecast

2″ to 4″ below 2500 feet

4″ to 8″ above 2500 feet

(+/-) 1″ error potential to imply a target snowfall of 3″ to 5″ at 2500 feet elevation (above mean sea level)

Snow accumulations will mainly occur between 6:00 PM Wednesday and 10 AM Thursday, with the bulk happening between 7 PM and 7 AM.

At the latitude of Wise, the solar angle at Noon is approximately 34.7 degrees for 27 January. This means that 1 unit of solar radiation striking the surface at a 34.7 degree solar angle above the horizon will spread out to cover 1.75 area units. This will diminish the intensity of insolation to just 57.1% of the value of a vertical beam.

In complex, three-dimensional terrain many slopes and valleys receive limited insolation (locally little to none) with such low sun angles due to shading by adjacent mountain ridges.

The Bottom Line, recent above average temperatures will not be a major factor given such a strong influx of cold air and limited insolation at this time of year in complex terrain.

Model Initialization Sounding For Wise At 7 AM_27 January 2021

While low clouds and a morning inversion mixed out, the mixing downward of drier air aloft is a key feature that will support a rapid deterioration of conditions by around and after 7 PM on Wednesday evening.

Model Forecast Sounding At 7 PM_27 January 2021

The 0 Celsius (32 F) wet-bulb temperature goes below freezing prior to the onset of precipitation, indicating that initial mix or rain will rapidly change into snow.

Model Forecast Sounding At 10 PM_27 January 2021

This will support a rapid development of widespread hazardous conditions, with thin icing beneath, during the evening in locations along and north to east-northeastward of the Cumberland Front (along the Tennessee Valley Divide).

High Knob Massif Forms Large Bulge On Appalachian Structural Front

Heavy snow is expected to develop and stretch from the High Knob Massif and Black Mountain corridor eastward along the Tennessee Valley Divide, with models centering the core of heaviest snow on the Mountain Empire Airport region of the Tennessee Valley Divide.

My caution for significant run-off will continue into Wednesday, with streams still above Red Alert levels.

Caution For High Water Levels On Streams Draining The Wise-Scott-Lee Border Area Into Wednesday

ROARing Water Levels – Big Stony Creek of High Knob Massif

Snowstorm Potential Next Week

A Miller B Winter Storm will develop to impact the mountain region beginning late this weekend into early-middle portions of next week.

Generalized Features Of A Miller B Winter Storm

This typically means initial frozen precipitation (snow, sleet, freezing rain) that changes into a cold rain at lower-middle elevations (below 3000 feet), with cold rain or freezing rain in upper elevations.

Initial snow-sleet tends to change to sleet or freezing rain along the eastern slopes of the Appalachians, with only rain occasionally falling on high summits (standing in above freezing air aloft) following initial frozen. Farther northeast, into the central Appalachians, deeper cold air can support mostly snow or snow-sleet.

A transition back to snow occurs as the secondary low becomes dominant. The track-intensity of this low then dictates how much snow falls on NW-N upslope flow.

In the BIG Picture…

Signals for a major winter storm began showing up a couple weeks ago, and I initially highlighted this potential in my 011321 Forecast Discussion.

Models have struggled with this pattern, but seem to have finally found the wave that may generate a major winter storm whose impact will likely be greatest from northern Virginia into New England. This is not the only major storm potential showing up in the extended.

012321 Forecast

Reference Mid-Winter 2021_High Knob Massif for a recap of recent conditions, as well as a 2020 precipitation update.

Caution For High Water Levels On Streams Draining The Wise-Scott-Lee Border Area And Portions of Dickenson-Buchanan Counties Through Tuesday

A general 1.50″ to 2.00″+ of rain has combined with snow melt to cause elevated levels on creeks draining the High Knob Massif (which are ROARing).

Elevated stream levels may also be encountered locally within Dickenson and Buchanan counties (but with no snow melt contribution, levels are generally not as high as along the Wise-Scott border).

Big Stony Creek was only 12″ (1 foot) below flood stage (6.5 feet) at 4:00 AM on Tuesday (26 January 2021) and continuing to rise.

Big Stony Creek of High Knob Massif

Caution is advised for swift, dangerous water through Tuesday (26 January 2021).

An ALERT for accumulating snow will likely be needed for Wednesday Night into Thursday.

ALERT For The Potential Of Strong Water Level Rises On Creeks, And Ponding Of Water In Low-lying and Poor Drainage Areas, From Monday Into Tuesday (25-26 January 2021)

While highest probabilities of strong water level rises will be across central-southern Wise, northern Scott, and adjoining areas within Lee, Harlan & Bell counties, the likely development of convection (thunderstorms) will increase the chance in all locations.

Storm Prediction Center Outlook_7 AM Monday to 7 AM Tuesday

Terrain models are now trying to show the orographic couplets that I had anticipated.

NAM 12 KM Model Run_Total Precipitation Forecast

Note the orographic wave clouds that are already present above the High Knob Massif as wind fields increase in advance of this system.

Wave Clouds Above High Knob Massif_3:55 PM_24 January 2021

Convection could either enhance or diminish these terrain couplets depending upon how it develops.

Previous Discussion

Weather Headlines

The potential for heavy rainfall amounts are being monitored for Monday into Tuesday (25-26 January 2021), with local terrain enhancement becoming possible on strong S-SW low-level inflow.

NAM 12 KM Model Run_1 PM Saturday_23 January 2021

I like the latest NAM Model idea of generating a secondary zone of enhanced rainfall amounts. This fits documented, past climatology of events with strong SW 850 MB inflow that acts to generate enhanced low-level terrain convergence across the High Knob Massif and Tennessee Valley Divide of the Cumberland Front.

The Appalachian Structural Front (Cumberland Front)

It is not just orthogonal flow that must be recognized, with cross-contour ageostrophic flow developing locally due to terrain generated drag . With that noted, the backbone of the High Knob Massif also turns easterly from the Head of Powell Valley to generate a greater orthogonal component.

NAM 12 KM Model_850 MB Streamline Forecast_4 PM Monday (25 January)

Models like the GFS are farther north, with less than 1.00″ of rainfall predicted locally, but it does have a bias of missing terrain convergence along the Cumberlands.

The European Model, and numerous ensemble members, also supports the idea of a secondary maximum in rainfall that is generally aligned with the Cumberland Front (locally) and Cumberland Plateau (farther southwest in Tennessee).

Enhanced Run-Off Potential (26-27 January 2021)

GOES-16 Visible Image At 2:11 PM on 23 January 2021

Although snow cover is limited regionally across the southern Appalachians, there is a significant amount of water being held locally in a snowpack at highest elevations in the High Knob Massif.

Snowpack In Heads of Lake Basins

A good aspect, as I have noted many times in the past, is that watersheds such as those drained by Big Stony Creek, Little Stony Creek, Benges Branch, and South Fork of Powell River all contain lakes and wetlands that initially capture water from their snowiest basin heads. Although all lakes are currently overflowing, this will still slow run-off.

Rainfall will be absorbed by the snowpack, such that unless the worse case scenario develops (torrential rain amounts with rapid snow melt) run-off should be able to be handled.

It will likely push steep creeks to ROARING levels, and will thus need to be closely monitored by both local residents and official, EMS personnel.

Late Week Snowfall Potential

GFS Model 500 MB Anomaly Forecast_7 AM on Thursday_28 January 2021

A second wave developing in wake of early week rainfall has the potential to generate significant snowfall by late Wednesday into Thursday (28 January 2021).

Favorable Upper Air Dynamics_10 PM Wednesday_27 January 2021

Although upper air dynamics appear favorable for heavy snow, the placement, timing, and intensity remain to be worked out for the Mountain Empire.

Stay tuned.

011921 Forecast

Weather Headlines

Reference Mid-Winter 2021_High Knob Massif for a recap of recent conditions, as well as a 2020 precipitation update.

ALERT For Accumulating Snow During The Predawn To Mid-Morning Hours Of Thursday (21 January 2021)

The highest risk for accumulating snow is expected along and mainly south of a Breaks Interstate Park to Bluefield line across far southwestern Virginia.

Hazardous Road Conditions Are Expected Due To Cold Surface Temperatures As Well As Moderate To High Snowfall Rates Associated With This Fast Moving System

Accumulations from 0.5″ to 2.5″ are expected, the bulk of which will fall during the predawn to mid-morning period of Thursday.

Locally higher amounts are possible.

Updated at 9:30 PM on 20 January 2021…USA models are now coming into line with the foreign models and are finally realizing the snow accumulation potential with this fast moving southern wave.

It is interesting to observe that USA based models have been slow to show accumulating snow with this system, in contrast with the European, Canadian, and German based models that all predict a period of accumulating snow Thursday (essentially all 51-members of the European Ensemble group agree).

Mountain Snow Cover & Local Snowpack Surrounded By A Bare Landscape

Previous Discussion

Wednesday Into Wednesday Night

Cold air will return Wednesday (20 January 2021) on WNW-NW flow. Limited moisture will keep upslope flurries and snow showers mainly light.

Generally less than 1″ of accumulation is expected, even at highest elevations, with little to none in many locations.

Locations northeast of the Virginia-West Virginia border, along and west of the Allegheny Front, will have a general 1″ to 5″ of snow with some Great Lake moisture transport.

Predawn-Morning Hours of Thursday

The potential for a morning burst of moderate snow is being monitored for Thursday (21 January 2021) as a southern tracking system passes mainly south of the Mountain Empire.

Locations along and south of the High Knob Massif appear to be at highest risk for a morning accumulation of snow, however, this remains to be determined.

Stay tuned.

Major Storm: Early-Middle of Next Week

Heavy Precipitation Potential Being Monitored

The potential for heavy precipitation is being monitored for next week. While rain and snow may fall, the bulk of this event is currently leaning toward rain in modeling as milder air surges across the Mountain Empire.

This raises a concern for heavy to excessive run-off with snow melt from the upper elevations. Once again, stay tuned for later updates on this storm potential.

011321 Forecast

Weather Headlines

ALERT For Accumulating Snow Sunday Night Into Monday With Hazardous Conditions Developing

This 4:00 PM update Sunday is to stress that increasing snow showers and squalls will be observed into Sunday Night-early Monday, with hazardous road conditions developing once again as instability increases.

Forecasters Need To Recognize The Pattern

Snow will accumulate from the floor of the Powell River in Lee County, upward into highest elevations. I do not yet understand why the NWS idea is that only elevations over 3500 feet will have significant accumulation?

With bitter air aloft moving over later tonight, this will be transported downward in convective snow showers and squalls to cool the boundary layer – especially within the zone where SW-WSW air flow trajectories must rise upon approaching the High Knob Massif.

The zone of heaviest snow observed so far (2.5″ to 6″) has been along and southwest of the High Knob Massif and Tennessee Valley Divide in far southwestern Virginia, because this has not been, and will not be, a NW Flow snowfall setting.

Previous Forecast (Still Valid)

ALERT For Periods Of Snow Friday Night Into Monday With Reduced Visibilities In Heavier Snow And Hazardous Road Conditions

This update at 3:40 pm on Friday is to cover the development of snow showers, with heavier squalls (already in my forecast) developing Friday night into Saturday with hazardous conditions. This follows a general 1″ to 2″ of snow Friday morning at elevations above 2000-2500 feet, with locally 3″ at the highest elevations in the High Knob Massif.

New Snow In Wise at 12:05 PM_15 January 2021
Eagle Knob of High Knob Massif (6-10″ depth)_11:47 AM_15 January 2021

Snow showers and locally intense snow squalls will be likely from the predawn into the afternoon of Saturday (16 January 2021). An injection of Great Lake moisture will combine with bitter air aloft and steep lapse rates above the mountains to support snowfall with general 1″ to 4″ amounts expected.

Upon additional analysis, I am now adding the potential of Thundersnow to my forecast for Saturday and again for late Sunday into Monday.

For those who ask, I have NO, absolutely NO, explanation for why the MRX NWS Forecast Office has left Wise County out of the advisory, or why they leave northern Scott and northwest Lee, as well as Dickenson (RLX NWS FO) for this type of setting.

The error in leaving the documented snowiest terrain in Virginia (central-southern Wise) out of a setting like this is not explainable or based upon documented scientific data and certainly is in opposition to climate research (including not only mine but others).

I think forecasters are under-estimating the potential of this upcoming setting with a risk for whiteout type squalls that could, at least locally, contain lightning and thunder.

Locations that receive repetitive squalls could end up with higher snowfall totals than in my current forecast (which already are the highest being predicted).

Total Snowfall Forecast
(Friday AM through Monday AM)

2″ to 4″ below 2000 feet
(Less than 2″ in downslope sites)

4″ to 8″ above 2000 feet
(Locally higher amounts)

Snowfall will occur with separate waves,
the first during Friday morning, the second
late Friday night into Saturday and the third
wave later Sunday into early Monday.

Previous Forecast & Discussion

ALERT For Accumulating Snow Developing Between Sunrise And Mid-Morning Today (Friday Jan 15) Within Mid-Upper Elevations

Snow and mixed precipitation will develop Friday morning, with a general 1″ to 2″ expected at elevations above 2500 feet. Generally less than 1″ is expected at elevations below 1500 feet, except locally more along windward slopes north of the High Knob Massif.

An additional wave moving across the mountains will renew snow showers Sunday, with snow squalls again becoming possible beneath very cold air aloft by Sunday Night into Monday.

Additional 1″ to 3″ amounts will be possible with this wave from late Sunday into Monday.

Due to melting in between waves, especially at lower and middle elevations, total snowfall is expected to be greater than ground depths except at the highest elevations above 3300 feet.

Note that snow showers and flurries will be likely in between the main waves of more concentrated snow showers and squalls.

Extended Headline

Signals for a snowstorm are showing up in the extended range (20-30 January period); however, the placement, intensity, and timing remain uncertain and varied.

Stay tuned for updates.

011021 Forecast

Caution For Snow Developing Into Mid-Morning Monday (11 January) With Light Accumulations

A weakening storm system over the Deep South will spread a period of light to moderate snow across the area today, with light accumulations of 0.5″ to 2.5″ .

Locally higher amounts will be possible, especially along the High Knob Massif which will be near the axis of heavier snow (includes any snow into 12 January).

The highest probability of sticking snow will mainly be along and southeast of Pine Mountain (with little to no accumulations toward the northwest).

Hazardous conditions due to initially cold conditions will be likely, especially on secondary and untreated routes.

Some additional snow showers will be possible Monday night into early Tuesday as the upper level wave passes.

A beautiful view of this recent southern Appalachian snowfall following partial clearing on 10 January.

GOES-16 Visible Image_10:56 AM_10 January 2021

010521 Forecast

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).

Deep Snow on Eagle Knob of High Knob Massif_5:22 PM on 8 January 2021

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.

High Chaparral of High Knob Massif_11 AM_8 January 2021

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 on Eagle Knob of High Knob Massif_12:57 PM (8 January)

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.

Snowfall Forecast_8-9 January 2021

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.

Eagle Knob of High Knob Massif_12:48 pm_6 January 2021

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.

GEM Ensemble Mean Forecast_7 AM on 18 January 2021

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.

GFS Ensemble Mean Forecast_7 AM on 18 January 2021

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.