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

Update at 1:30 AM_7 February 2021

While I will not change my snow forecast numbers, having gone up to 6″ for elevations below 3000 feet when factoring in my error potential, with winds having gone quickly N-NE I do think the upper end of snow numbers could be reached or exceeded with upslope being maximized across Dickenson-Wise counties toward the High Knob Massif-Tennessee Valley Divide. I also think that the upper end may be topped in the Powell Valley of Wise County given this rapid shift to more northerly flow (as suggested below).

Certainly, Winter Storm Warning criteria (as I already had in my forecast) will be easily met and the potential for Power Outages is concerning at lower-middle elevations where snow density will be higher than at upper elevations (where air temperatures are colder and snow density lower and more wind driven).

Blowing-drifting (as often is the case) will be a factor at upper elevations.

A Miller A Type Winter Storm is expected to generate widespread, hazardous conditions from late Saturday night into Sunday.

ALERT For Heavy Snow Developing Saturday Night Into Sunday Morning (6-7 February 2021)

The majority of snow accumulation is expected to occur between 10:00 PM Saturday and 10:00 AM Sunday, with precipitation falling as all snow along and northwest to north of the Cumberland Front.

While Powell Valley in Wise County is south of (outside) this red line denoting the Cumberland Front, I want to stress that the highest probability of mixed precipitation exists here due to an enhancement of sinking air off of the High Knob Massif on easterly component air flow until the early overnight of Sunday (when winds shift to reduce sinking-warming, allowing all snow to fall).

Models are generally not predicting a decrease in snowfall southwest of Norton toward Big Stone Gap, but if the easterly component flow verifies then it will occur. If the easterly flow does not develop then a TIM Circulation will not form and variations will not be as large.

Another factor that could prevent a TIM circulation from forming would be if evaporative cooling within initially dry air is strong enough to overcome subsidence warming forced by the terrain. Evaporation is an endothermic process that takes energy out of the air in order to break the hydrogen bonds necessary to transform liquid water into vapor. This process is typically more limited (there is just so much energy available to be extracted from air), while subsidence warming will continue for as long as easterly flow streams across the high country into Powell Valley.

Due to this, lower snow amounts are expected southwest of the City of Norton toward Big Stone Gap. At the same time, by contrast, an enhancement of snow is expected above 3000 feet in the High Knob Massif.

Note that some models do not begin accumulating snow until Midnight or after, such that the bulk will fall through the overnight-morning hours of Sunday (7 February 2021).

Snowfall Forecast

3″ to 5″ below 3000 feet

6″ to 8″ above 3000 feet (*)

A (+/-) 1″ error potential implies
a 2″ to 6″ potential at elevations
below 3000 feet

1″ to 3″ in downslope locations
of the Clinch-Powell-Holston valleys

(*) – Locally higher amounts will be possible as orographic upslope combines with a topographically anchored rain-snow melting zone to generate a Thermally Indirect Mesoscale couplet of enhanced rising and sinking air (what I have identified in field research that I call a TIM Circulation) for a period into the early overnight of Sunday.

Example TIM events on the High Knob Landform are much more significant than what this is currently expected to be, with only a short period featuring a potential circulation. It is important not to neglect, however, in anticipation of bigger and much more impactful winter storms to come.

A sharp cut-off in accumulating snow is expected toward the northwest, approximately along the edge of foothill terrain where highest ridges begin dropping under 1300-1500 feet (above mean sea level) within the Appalachian Plateau province.

Heaviest snowfall is expected to develop along and eastward of the Cumberland Overthrust Block and southern Appalachian fold-thrust belt.

The above follows MEAN climatology of Miller A Type Winter Storms (it is not currently expected to be an inland variant-Miller A or totals would be MUCH greater).