While frozen precipitation types will be possible in all locations, a main concern today is frozen surfaces from more than a week of sub-freezing temps. Even if air temperatures are above freezing surfaces subjected to prolonged bitter cold will not have had time to warm prior to the development of precipitation.
There will be an enhanced potential for frozen precipitation forms, including snow, within the SW flow upslope zone within the High Knob Landform corridor where SW air flow rises, such that temperatures will remain colder than forecast models predict from the Tennessee Valley Divide ( Norton-Wise-Sandy Ridge ) into portions of Lee County. If snow develops within this zone then a general 1-3″+ will be possible; otherwise, other frozen types are expected from mid-morning into the afternoon.
Strong SW Winds Will Develop Sunday Night Into Monday At Middle-Upper Elevations Along The Cumberland Mountains
Although temperatures are expected to display near steady to rising trends across middle-upper elevation mountain ridges and exposed plateaus during Sunday Night into Monday, development of strong to ROARING SSW-WSW winds will continue to generate low wind chill values. Wind gusts of 25-50+ mph will become likely as a low-level jet interacts with higher elevations.
Bitter Cold Temperatures Will Continue Into Sunday Morning As A Large Temperature Spread Develops In The Vertical Between Frigid Valleys & Milder Ridges
A rapid Saturday evening-night temperature drop is expected in mountain valleys as ideal cooling conditions develop. Meanwhile, higher mountain ridges will begin to experience a slowing of falls and even rising temperatures overnight into Sunday morning as winds shift S-SW. This will generate a large vertical temperature spread between colder valleys that drop below 0 degrees and milder ridges which rise upward through the 10s.
Saturday Night Into Sunday Morning
Mostly clear. Bitter. Large vertical temperature difference developing between frigid valleys and ”milder” mountain ridges. Light winds becoming S-SW along high mountain ridges overnight-into morning at 5-10 mph. Temperatures varying from below zero in colder mountain valleys and on highest peaks ( early ) to the single digits, then rising thru the single digits into the 10s along higher mountain ridges overnight into morning. Wind chills from 5 above zero to -15 degrees below zero on mountain ridges.
Sunday Morning Through The Afternoon
Increasing mid-high altitude clouds. S-SW winds increasing to 5-15 mph, with higher gusts. Temperatures varying from the mid 20s to low-mid 30s. Wind chills in the 10s and 20s.
Sunday Night Into Monday Morning
Mostly cloudy. Becoming windy. Evening temp drop in sheltered valleys, then rising temps possible with mixing overnight into morning. SSW-SW winds 10-20 mph, with higher gusts, on mountain ridges-exposed plateaus below 2700 feet. SW winds 15-25 mph, with higher gusts, along mountain ridges above 2700 feet. Temperatures mainly in the 20s, except dropping into the 10s in sheltered valleys prior to rising by morning. Wind chill factors in the single digits and 10s.
Monday Morning Through The Afternoon
Cloudy with snow, sleet, freezing rain-rain developing. Icy conditions likely on many surfaces. Windy. SW winds 15 to 25 mph, with higher gusts ( decreasing beneath the top of any low-level inversion formation ). Temperatures in the 30s, then dropping to around or below freezing within the SW upslope flow corridor along and southwest of the High Knob Massif-Tennessee Valley Divide as well as beneath any low-level inversion. Wind chill factors in the 10s and 20s. Dense fog formation possible.
A January thaw period next week is expected to give way to bitter cold once again by late next week-weekend ( January 12-14 period ) as the winter pattern locks back into the eastern USA.
Weather Discussion ( Nasty )
Early Overnight Monday Update
Strong-roaring SSW-SW winds are blowing across the high terrain in advance of developing precipitation downstream of the mountains.
Black Mountain Mesonet – Elevation 4031 feet
Strong and gusty winds will continue to mix downward to below the 2700 foot level into middle elevations overnight into Monday morning.
Flatwoods Mountain Mesonet – Elevation 2774 feet
Dry air in lower levels of the atmosphere may keep precip from reaching the ground until the mid-morning period, with evaporative cooling helping create a setting where various types of frozen precipitation will be likely.
The best chance for snow, with possible accumulations, will be within the SW air flow upslope zone from the Tennessee Valley Divide-High Knob Massif southwest into portions of Lee County where air flow becomes orographically forced.
Unless a strong inversion develops, limiting mixing, downslope flow could help reduce frozen amounts in the Pound-Clintwood to Haysi-Grundy zone; however, this is not a typical setting with all ground surfaces being frozen to increase the hazardous aspect with only light precipitation amounts.
Previous Discussion
Another bitterly cold night, especially in mountain valleys, will be observed into Sunday morning before conditions get nasty in another way.
High Knob Massif Webcam – University Of Virginia’s College At Wise
The best radiational cooling conditions of this great cold wave to date will be observed tonight into Sunday morning, especially within mountain valleys where temps will again drop below zero ( far below in high elevation valleys where temperatures were already dropping to 0 degrees at 6 PM ). Lower elevation valleys, like in Clintwood, with less snow cover were at 10 degrees at 6:00 PM Saturday.
Saturday ( January 6 ) MIN Temperatures
Nora 4 SSE -1 degree
Clintwood 1 W -5 degrees
City of Norton -6 degrees
Black Mountain -7 degrees
*The coldest temperatures occurred within the snow covered expanse of the High Knob Massif, which I will highlight later.
Low temperatures into Saturday morning were frigid from top to bottom, with most locations across Wise & Dickenson counties falling to 0 degree and below.
Eagle Knob of High Knob Massif on Saturday – January 6, 2018
Saturday afternoon MAXS varied from 6 degrees on Eagle Knob of the High Knob Massif to 18 degrees in Clintwood. No wonder high valleys have had such a quick drop toward zero degrees with cold air drainage from the summits, with the temp on Eagle Knob falling back to 0 degrees at 6:15 PM.
The main difference tonight versus last night being that temps will not drop a lot more on the summits, but will begin to rise into the overnight and morning hours of Sunday as high valley temps continue to drop. A key factor to cooling being dewpoints within the 875-825 MB layer of the atmosphere for high country valleys surrounded by snow covered terrain.
NAM 12 KM Model Total Snowfall Forecast Next 60-Hours
After more than 40 years of recording mountain weather it has been learned well that coming out of a great cold wave is typically never easy, with strong winds causing low chill values being a typical ingredient having to be endured as baroclinicity increases ( horizontal temp gradient packs ) and generates a pressure gradient that cranks up strong winds to push against the mountains and drive the bitter air away ( an especially nasty process for everyone living within mid-upper elevations ).
GFS Model Total Snowfall Forecast Next 60-Hours
Models will continue to struggle as they try to resolve what is going to happen with the vertical temperature profile in the atmosphere, but the fact remains they they simply will not be able resolve what 10-14 days of below freezing temps have done to surfaces ( freezing the ground deep ) which will not even begin to thaw prior to any precipitation.
An ice up on surfaces, a period of snow to mix, formation of fog over cold ground are all on the table, perhaps even more significant SW upslope flow snow, as the battle between warm air advection and arctic air develops Monday.
Roads treated with new cold weather solutions will certainly do better than many back roads and other surfaces which are not treated in such ways. No surface; however, should be taken for granted and everyone will need to be on high alert Monday with respect to decks, walkways, roads, etc…until the icing threat passes.
One aspect appears certain, given this great cold wave has not been just concentrated in the mountains, the typically milder domain of the Great Valley will also be subjected to potential chaos as this transition occurs.
