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 11:30 PM on 4 February 2021

Extreme caution should be taken on roadways above 2500-3000 feet in the High Knob Massif as snow-sleet has now changed to freezing rain with a drop in surface temperature to 27-28 degrees.

A few impacted roadways include:

State Route 619, State Route 706, State Route 699, Route 237, Route 238, Route 822 with the freezing level generally being a little lower on the Scott County side versus Wise County side due to strong upslope cooling on S-SSW winds which has dropped air temperatures below freezing.

A change back to snow may occur during the overnight, especially at the highest elevations.

Some tree limbs have also been broken due to high winds during the evening.

A mixture of sleet & rain has mainly changed to a cold rain at lower-middle elevations, but a quick temperature drop into the predawn should be respected for the possibility of black ice formation at lower elevations.

ALERT For Strong S-SW Winds Thursday Night Into Friday Morning – Especially At Elevations Above 2500 Feet And Locally Within Mountain Waves

Wind gusts to 50+ mph will be likely at highest elevations and locally with mountain waves to the north and northeast of the High Knob Massif-Black Mountain area across Pine Mountain and higher ridges in Dickenson-Wise counties (where many people live).

ALERT For Wintry Precipitation (Snow-Sleet-Freezing Rain) Developing Thursday Night Into The Overnight Hours Of Friday (Especially At Elevations Above 3000 Feet)

Snow-sleet accumulations varying from a dusting up to 1-3″ will be possible above 3000 feet. This spread is due to the unknown amount of specific precipitation type.

Wintry precipitation is expected to develop Thursday Night into the overnight hours of Friday at mid-upper elevations across southern Wise County, northern Scott, and highest portions of Lee (mainly centered upon the High Knob Massif and highest ridges of Black Mountain) due to evaporative and strong adiabatic upslope cooling on SSW-WSW winds.

While this alert is centered upon an 80-square mile zone with elevations above 3000-3300 feet, where 100+ families live in the High Knob Massif, there will likely be a mix of precipitation types in surrounding locations.

If only a single family lived above 3000 feet it would matter. Everyone counts. All must be treated equally. So, 1, 1000, or 10,000+ it does not matter. They all deserve to be treated the same with forecasts.

To not include any area within weather advisories (of any type) for impacts because it possesses a more limited population is a form of Environmental Injustice.

It is Human Rights Injustice.

High-resolution models are seeing the upslope cooling where they are programmed to recognize it, such as in the Snowshoe area of eastern West Virginia.

There is no frontal passage between Snowshoe and High Knob, and wind directions remain S-SW, but model bias and errors (which I have documented over, and over, and over again in the past and observed most recently during 30-31 January) show warming instead of cooling over the High Knob Massif.

I have no doubt cooling will occur up to 850 MB, but if warming above that level is strong enough to overcome rising air with orographic ascent (often along a standing mountain wave) then freezing rain and not snow will be observed at highest elevations.

The massif tends to generate standing wave clouds, with a upward ascent region that can lift air well above its physical height. That is the key to producing snow when forecast models predict only rain, or mostly rain, in these settings.

Even if all snow falls, it will generally only result in 1-3″ of accumulation, so what is the big deal?

It for recognition of bigger events, and in respect of those (every single person) who live, work, hike, travel across, etc. the High Knob Massif area in all seasons.

Bigger events have been observed many times in the past on SW flow, most recently during 30-31 January 2021 and well documented during February 2015 when ROARing SW winds accompanied a blizzard across the high country (above 3000 feet).

Extreme Winter Potential

Discussion of an extreme winter potential is not HYPE. It is real, very real. The problem, ongoing changes between the stratosphere-troposphere has models in chaos until the two fully couple together.

Observed changes this winter in the Polar Vortex appear to be unique in the observational record (since 1969), and while I will not get into the details here, an excellent discussion is given by Dr. Judah Cohen in his Arctic Oscillation and Polar Vortex Blog.

I expect the true potential of this upcoming winter pattern to become much more clear in a few more days.

A Miller A type winter storm can be a very potent snow maker for the Mountain Empire, so this setting will need to be closely followed as it evolves into this weekend.

While models are trending back toward a southern Appalachian fall of snow this weekend, I think they will also begin to better resolve an influx of bitterly cold, arctic air that will dramatically change the landscape across the central-eastern USA into mid-February.

As I noted way back at the beginning of this winter, a fight has been ongoing between Pacific Ocean Basin factors (unfavorable for eastern USA winter) and Atlantic Ocean Basin factors (favorable for eastern USA winter conditions).

It is not that the NAO is going negative, it has been negative since late December.

The Arctic Oscillation (AO) has been negative all winter as it is more intimately linked to the Stratospheric Polar Vortex. Reference Sudden Stratospheric Warming.

The AO is likely to remain negative through the final warming and Spring 2021.

The headline news, factors across the Pacific Ocean Basin are becoming more favorable for eastern USA winter (and not fighting against the -AO and -NAO as strongly as recently observed).

The EPO remains mixed, and not as favorable.

The Bottom Line…An extreme winter potential exists heading into mid-late February. Whether or not it is fully realized in the Mountain Empire remains to be seen.

Previous Discussion

Weather Headlines

Upslope flurries and light snow have redeveloped during early hours of Wednesday as a plume of Great Lake moisture is allowing clouds to form.

A dusting up to 1″ will be possible through this morning (Wednesday, 3 February 2021).

An ALERT for High Winds will be likely for Thursday Night into early Friday as ROARING and potentially damaging SSW to WSW winds develop.

A low-level jet with core speeds of more than 70 knots will generate Hurricane Force wind gusts at highest elevations, and locally within the descent region of mountain waves that develop across the High Knob Massif-Black Mountain corridor Thursday Night into the early hours of Friday.

A strong pressure gradient will generate strong winds centered on the sunset Thursday to sunrise Friday period. This will also cause blowing snow along high, exposed mountain ridges. At least localized power outages will be possible.

Wind driven snow, supported by strong orographic lift, will also be likely at upper elevations in the High Knob Massif during this time. How low will snow levels drop? That is what I will be looking at on new model runs.

Due to strong descent, only rain is expected in locations north-northeast of the High Knob Massif and Tennessee Valley Divide (models generally predict rain, but like the heavy snow that fell into 31 January, above 3000 feet, models will be wrong unless adjusted for orographics).

Stay tuned for updates.