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.

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.

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.

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.

Extreme Winter Potential

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

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.

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.

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).

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.

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.

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.

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.

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.

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).

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

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.

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.

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.

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.

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

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

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.

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.

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.

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)

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.

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

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).

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.

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).

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

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.

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.

History Of Christmases Past
(1964-2019)

An ALERT For Severe Conditions Developing From Christmas Eve Into Christmas Day

Extremely hazardous conditions are expected to develop between 3:00 to 5:00 PM, worsening into this evening with high snowfall rates and plunging air temperatures.

Plan to be in place, where you will stay tonight, before this critical period of 3 to 9 PM on Christmas Eve.

Snowfall Forecast

Along And W-NW Cumberland Front

Christmas Eve PM to Christmas AM
General 4″ to 8″
(Locally higher amounts)

Christmas Sunrise-Sunset
Additional 1″ to 4″
(Locally higher amounts)

Clinch-Powell-Holston River Valleys

Christmas Eve to Christmas AM
General 2″ to 4″
(Locally higher amounts)

Christmas Sunrise-Sunset
Additional local accumulations
(in instability snow squalls)

Strong wind gusts combined with a temperature around 40 degrees to generate melting snow atop the High Knob Massif during afternoon hours of 23 December 2020, although, wind chills made it feel significantly colder (nothing like what is coming for the Christmas Holiday).

Heavy Snow & Bitter Cold Christmas

A period of severe winter weather is expected to develop during Christmas Eve afternoon into Christmas day.

The following are preliminary thoughts on the evolution of this event.

1). Rain will change to snow Christmas Eve afternoon with a temperature plunge into the evening. Hazardous travel conditions are expected.

2). The potential for enhanced snowfall along the front is being monitored, with the European and Canadian models being most aggressive in developing a wave of low pressure along the arctic front Christmas Eve.

Christmas Eve Day Model Update

I have included an array of model predictions, to include their Kuchera forecast where available.

The Kuchera Method takes into account how snow amounts change with air temperature versus the much more rigid 10:1 method that says 10″ of snow = 1.00″ of water.

In this case, due to strong cold air advection, snow density will rapidly drop with high snow to water ratios (that is, a lot of snow for limited water) developing into this evening and Christmas day.

3). Convective bursts of heavy snow are likely following the frontal snow band between midnight and sunset on Christmas day, beneath extremely cold air aloft.

It is because air will become outrageously cold aloft that snow amounts will generally be higher than most models predict for Christmas day, with potential for whiteout type snow squalls (bursts) in very low density (high snow to water ratio) snowfall.

While orographic forcing tends to make these squalls more productive and frequent over and upstream of windward mountain slopes and major barriers, strong vertical lapse rates during day time (especially) can cause them to form with instability within any location.

4). This will not be a classic NW flow setting across the southern Appalachians, with WSW-WNW trajectories that are not Great Lake connected.

Cold air aloft, and steep lapse rates, will help to make up for the lack of more perpendicular flow with cross-isobaric convergence favored along the main mountain barriers (especially the Cumberland-Allegheny Front and windward side of Blue Ridge).

Low snow density (high snow to water ratios) will work with lingering moisture to continue accumulating snow (especially in bursts) through Christmas day.

5). Dangerously cold conditions are expected through Christmas day, with air temperatures in the single digits and teens combining with gusty winds to generate single digit and below zero wind chill factors.

ALERT For Strong SSE-SSW Winds Developing By Late Wednesday Afternoon Through Christmas Eve Day Morning (23-24 December)

Strong winds will begin in upper elevations by late Wednesday afternoon, with downward mixing across the area into Thursday morning. Mountain wave winds in favored breaking zones (downward momentum transfer) will enhance gusts during Wednesday evening into the overnight.

A strong pressure gradient in advance of a major winter storm will generate strong winds across the mountain area Wednesday night into Thursday.

More Storms In The Pattern

Both the European (stronger) and GFS model groups show important features heading into the beginning of January 2021. High-latitude blocks and a classic negative phase of the North Atlantic Oscillation.

The Greenland Block is important for USA storms, like the present Christmas Holiday snowstorm and signals more storms in the pipeline ahead.

Storm potentials are currently showing up just prior to and following New Year (at least one of these could be a major snowstorm).

The Ural Block could be important for the longer-term via enhanced wave forcing that could work to weaken the Polar Vortex, increasing the threat of major arctic intrusions into middle latitudes.

Previous Discussion

Winter Storm For Christmas 2020

There is now a higher than average confidence level for a white Christmas 2020, with both the European (which I can not legally show) and GFS models (and ensemble means) being in rather amazing agreement at 500 MB across the Northern Hemisphere by Christmas.

Details remain to be worked out, of course, but this is part of a now long advertised pattern where features in the Atlantic Ocean and at high latitudes in the Northern Hemisphere are beginning to dominate over forcing from the Pacific Ocean Basin (which is now trending more favorable for wintry, eastern USA conditions).

In other words, the push-back from the Pacific Basin against very favorable conditions across the Atlantic Basin is not as strong now as it has been, favoring a colder and more wintry setting over the eastern USA into the New Year than previously suggested.

An aspect that will be different with this event from previous December systems to impact the southern Appalachians will be the advection of bitterly cold air, with very low snow density likely aiding amounts that fall across the mountains as temperature plunge into morning hours of Christmas day.

Although temperature means for this month (through 20 December) have been near to a little below average, air temperatures during snowfall events have been marginal across the southern Appalachians for snow with exception of the early December NW flow snow.

December 2020 Snow Events (Elevation Biased)

Much more snow has fallen at highest elevations than even within lower sections of the upper elevations (below 3500 feet), and adjoining middle elevations (2000-3000 feet), due to air that has only been marginally cold enough to support snow.

ALERT For Possible Hazardous Travel Early Wednesday then For Accumulating Snow Wednesday Night Into Thursday Morning

Frozen precipitation types will be possible at the onset of precipitation early Wednesday prior to a change into rain. Precipitation will then change into snow, from highest elevations down, beginning Wednesday afternoon into Wednesday night.

More limited wrap-around moisture, and a small change in air flow trajectories, has resulted in a reduction in forecast amounts through 17 December at all elevations.

Snowfall Forecast
(16-17 December 2020)

Generally 1″ or less below 3000 feet

1″ to 2″ at elevations above 3000 feet
(with locally higher amounts)

Target Snowfall: 1″ [(+/-) 1″ Error Potential] for Norton-Wise. This implies a dusting to 2″ of snowfall will be possible into 17 December 2020 across Wise and Dickenson counties. The greatest snowfall amounts, of 2″ or more, are expected at highest elevations in the High Knob Massif where rime ice is also expected.

Reference Early Winter 2020 for a brief recap of the recent event.

Miller B Type Winter Storm

An initial low that moves west of the Appalachians weakens as a secondary low begins forming along the Atlantic Coast. This second low may then impact the Northeastern USA, especially if the track is inside the 40 degrees N / 70 degrees W benchmark point, with heavy snow and wind (generally referred to as a Nor’easter).

While Miller B type Nor’easters can occasionally have a large impact locally with icing and heavy snow, (especially at upper elevations in the High Knob Massif), it is the Miller A type Nor’easters that tend to be crippling winter events for the local mountain region.

There are important aspects to be monitored, with these being climatological characteristics (all of which apply, at least partially, to each event of this type).

1). Evaporative cooling with dry air initially in place could support snow or a mixed period of frozen types at the beginning and front of the surface-reaching precipitation shield (early Wednesday).

2). The most significant snow and/or icing in far southwestern Virginia typically occurs at upper elevations in the High Knob Massif.

3). To the east, cold air wedging and upslope on easterly component low-level flow typically results in more prolonged frozen types across western North Carolina and the eastern portion of southwestern Va.

4). To the northeast, deeper cold air in the vertical typically supports more snow from the Greenbrier Valley of eastern West Virginia north and east along the West Virginia-Virginia border area.

5). Wrap-around and orographic upslope snow on the backside of the storm is typical, and sometimes can be very significant in favored upslope locations as temperatures drop with cold air advection.

For this event, wrap-around moisture is expected to be limited versus more productive events already documented in history.

Potential Christmas Winter Storm

The big news in the weather world, at least for those with hope for a white Christmas, is a signal for the potential (emphasis this far away on potential) development of a Christmas Holiday winter storm.

Although negative phases of the Arctic and North Atlantic oscillations are expected to continue (as they are currently negative), it is the formation of a positive Pacific North American oscillation phase that is a new trend that could aid deepening of a eastern USA upper wave (i.e., aid storm formation).

The persistence of blocking near Greenland and in the Ural Mountain region is an important aspect that is also working to generate atmospheric waves capable of impacting the Polar Vortex, which in the long-term (January-February) may influence future conditions across eastern North America.

Stay tuned for later updates.

ALERT For Heavy, Wet Snow Developing Along And N-NW Of The Cumberland Front During The Predawn-Morning Hours Of Monday (14 Dec 2020)

NOTE: The main departure from this will also include the area along and northwest of Clinch Mountain, northeast from Brumley Mountain, for the heavy snow potential

I am concerned about a crippling fall of snow. The potential is there based upon the setting and well documented, past events. Crippling in terms of the snowfall rates and also for the possibility of power outages. To be honest in every way, the potential exists for either a non-event or a crippling event. Reality may be in between these extremes, however, I must make everyone aware of this crippling threat.

Snowfall Forecast

2″ to 6″ below 3000 feet

6″ to 10″ above 3000 feet
with locally higher depths

Target Snowfall: 4.0″ in Norton-Wise (+/- 2.0″ error potential) implying the potential for 2″ to 6″ of snowfall through early afternoon Monday (14 December).

The deepest snow depths of more than 6″ are expected at upper elevations in the High Knob Massif and highest portions of Black Mountain. The majority of precipitation is expected to be snow at the summit level of the High Knob Massif, where 10″ or more could accumulate in a furious fall of heavy snow.

The above forecast is for locations along and northwest-north of the Cumberland Front.

This first wave presents a relatively easy forecast for locations toward the south into the Clinch, Powell, and Holston river valleys where it will be mainly a rain-mix event with limited to no snow accumulation, and to the northeast along the Allegheny Front of the highlands of eastern West Virginia where upper air temperatures will be colder to support mainly a snow event.

In the middle along the Cumberland Front, northeast from Cumberland Gap, it will be a war and the forecast bust potential will be much higher than average.

Forecast models are literally divided between a non-event and a heavy, pounding event that could include potential for power outages and downed trees.

Rain will overspread the mountain region initially, then processes that work to cool the air will become the main focus for locations along and just north and northwest of the Cumberland-Allegheny Front.

This forecast is leaning toward more wet snow based upon already observed, documented past climatology of events possessing an analogous surface low track and surface to 850 MB air flow trajectories.

Although no two forecast settings are identical, the reasoning for my lean toward wet snow is sound based upon past observed events and meteorology.

Column cooling, supported by dynamics, will develop downward via entrainment of cold air at higher levels as low-level northerly upslope flow develops to begin the process of low-level cooling via orographic lifting.

If these processes phase earlier in the event, a crippling snow could occur versus if they occur later during the event (that is the big unknown that gives this forecast setting a higher than average bust potential).

Anyone who is a student of past climatology should recognize this crippling potential immediately, given many have occurred and a few are even documented on the High Knob Landform website (even though it only came online during Summer 2009).

Storm Report At 1:50 AM on 14 December 2020

Snow began falling at the summit level of the High Knob Massif by around 1:00 AM, with sticking to roads by 1:30 AM (a gravel lot above at 1:50 AM).

It is likely that roads will become near impassible at these upper elevations by morning as winds shift and become stronger out of the north.

Snowfall Potential Increasing

High-latitude blocking over Greenland is expected to impact upper air waves moving across the continental USA next week.

This is part of a pattern that currently features favorable Atlantic Ocean Basin teleconnections for wintry conditions across the eastern USA, with negative phases of both the Arctic and North Atlantic oscillations.

The European ensemble mean is more negative than the GFS ensemble mean, but there are signs of warming during Christmas week. That remains to be seen as time gets closer to the Holiday period.

An initial (weaker) wave will support the first potential for accumulating snowfall into Monday (14 December), with a stronger secondary wave being monitored for the middle of next week (16-17 December 2020).

While the Pacific Ocean basin is supporting teleconnections in opposition to wintry conditions across the eastern USA, in general, there has been a trend toward +PNA by the middle to end of this coming week (centered on 17-18 December 2020).

Warm forcing from the Pacific Basin will attempt to win out in the longer term (Christmas Week into January 2021).

Potential Impact of First Upper-Wave

Advisory to local warning level amounts of snow are being highlighted by different model groups for an upper wave predicted to cross the Appalachians into Monday, with accumulating snow developing locally between midnight-sunrise on Monday (14 Dec 2020).

The European Model group (not shown) and NAM Model group are in general agreement with placement of an axis of moderate to locally heavy snow along and northwest of the Allegheny-Cumberland Front. The new ICON (German) Model and GFS run are also in basic agreement.

The Canadian Model (GEM Operational) remains the single model of the big groups to predict very little to no snowfall through Monday.

Extended Outlook – Toward Christmas

Although the extended outlook to Christmas, released today, from NOAA looks like a blow-torch, all hope is NOT yet lost for a White Christmas.

Above average precipitation is a notable indication of storminess, and there are some other signs of a variable up-down pattern as forcing factors in the Atlantic (cold) and Pacific (warmer) continue to battle for control.

Stay tuned for later adjustments.

Autumn Color 2020_High Knob Massif Area

Autumn color has advanced significantly across the area since the beginning of this week, with conditions on 9 October featuring an array of nice colorations across many locations along and north of the High Knob Massif (Clintwood-Pound to Norton-Wise), with this weekend (10-11 October) through next weekend (17-18 October) expected to offer some of the best color above 3000 feet.

If color continues to advance rapidly below this elevation, a general peak will occur by 17-18 October in locations along and northwest-north-northeast of the High Knob Massif.

As autumn color begins peaking at upper elevations, remnant rains from Hurricane Delta will overspread the mountain region this weekend, with additional showers and thunderstorms into early next week.

Moderate to heavy rainfall, wind driven within upper elevations, will be detrimental to some leaves.

Time will tell what impact it has on the general peak, with brightening color on some trees as other trees experience leaf drop into next week. Trees with bright color currently, standing within exposed locations, will be at greatest risk of leaf fall.

Models are forecasting a general 1.00″ to 4.00″, with locally more in favored upslope locations and less in downslope locations on general SSE-SSW air flow trajectories across the southern Appalachians.

Heaviest rains are expected Sunday as the remnant core of Delta pushes across the region.

Colder Trend – Second Half of October

A colder trend in modeling is showing up during the second half of October, with high latitude blocking predicted to develop within positions that favor enhanced eastern USA upper air trough formation.