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.