My Forecast For Today ( February 14 )
An 8:50 PM Update: A brief break in Norton-Wise will give way to a meso-scale band of very heavy snow into the late evening-early overnight. Roads remain very bad and travel is discouraged!!! This snowband will overspread the area from northeast to southwest.
A Major Winter Storm Will Impact The Mountain Area From Sunday Into Tuesday With Significant Snow And Possible Mixed Precipitation Types To Rain
Target Snowfall of 6.0″ in Norton-Wise ( +/- ) 2″ Spread. This implies 4″ to 8″ of snowfall will be possible. This includes snow that falls up to the change on Monday and any additional snow that may fall following mix-rain into early Tuesday ( this final snowfall period is most favored in upper elevations ). As noted below, just a couple degrees of temp change aloft could make a large difference in snowfall amounts.
The Bottom Line – A Major Winter Storm will begin impacting the mountain region later Sunday. Snow will develop during mid-late afternoon-early evening and continue Sunday Night into Monday when mixed precipitation types to rain will become possible.
It should be noted that the outcome of this event may not be known until after the system develops. Arctic air currently in place greatly increases uncertainty as to when a change from snow to other types occur, with only 1 degree Celsius above 850 MB on the NAM Model, as an example, making the difference between snow and some other type of precipitation from sunrise on Monday to early afternoon. After 1 PM Monday there is some increase in confidence for a change to mixed precipitation and/or rain. This is a forecast that will have to be updated through Sunday.
If the bulk of this event falls as snow it could be a crippling event for the mountain area. If a change from snow to mixed types or rain occurs by Monday morning it will still be a significant snow but likely not crippling. Please stay tuned for later updates.
Overnight Into Sunday Morning
Increasing mid-high clouds. NW-N winds decreasing and shifting easterly into morning. MIN temperatures from -10 degrees below zero in colder valleys to around 10 degrees on exposed middle elevation mountain ridges.
*High mountain valleys in the High Knob Massif and other valleys with direct access to cold air drainage from deep snowpack have already dropped to around or below zero ( e.g., Norton to Coeburn valley corridor ). MINS to around -10 below zero will occur before clouds increase enough to stop falls as winds remain relatively light beneath Arctic High Pressure.
Lowering cloud bases with virga giving way to flurries and snow developing from top to bottom ( i.e., high elevations to valley floors over time ). SSE winds increasing to 5-10 mph, with higher gusts possible, along mid elevation mountain ridges & plateaus. SSE-SSW winds increasing to 15-25 mph, with higher gusts, along upper elevation mountain ridges. Temperatures varying from mid 10s to middle 20s ( coldest at highest elevations ). Wind chills in the single digits and 10s ( sub-zero in gusts along high crests ).
Tonight Into Monday Morning
Snow & blowing snow. Heavy at times. Possibly becoming mixed with sleet or freezing rain. SSE winds 5-15 mph, with higher gusts, on mid elevation mountain ridges-plateaus. SSW-SW winds 15-25 mph, with higher gusts, along upper elevation mountain ridges. Temps rising and becoming widespread in the 20s. Wind chills in the 10s & 20s on exposed mid-upper elevation ridges & plateaus ( single digits in gusts along mid-upper elevation ridges ).
Weather Discussion ( February 13-14 )
Late Afternoon Update
The only changes this afternoon were to begin stronger winds earlier than I had forecast by tonight, with gusts exceeding 30 mph atop the High Knob Massif and Black Mountain already, and to lower temperatures a little.
Initial evaporative cooling has dropped temperatures across the area, with recent recovery only at highest elevations on strong southerly winds ( into mid 10s with sub-zero chills in gusts ).
Roads have become very slick across the mountain area. Please do not travel unless absolutely necessary.
As of 4:00 PM temperatures were running around 6 degrees colder than forecast by the NAM Model for this time, so now it becomes a waiting game to see when warmer air aloft will change snow into mixed precipitation or dreaded freezing rain for places that remain below freezing.
Bowling Green in southern Kentucky recently changed from moderate-heavy snow to freezing rain at 28 degrees. So we can not rule out a transition from snow to freezing rain, which I have added to the forecast for the period from tonight into Monday AM.
My forecast snowfall amounts will hold for now. Stressing once again that lower end totals will be realized if a change to mix-rain occurs faster, while higher end tallies will occur the slower the transition from snow to mix and rain. That is the main reason for the 4″ spread in most amounts, with the ( + ) used for the potential that precip will be heavier than models have predicted and the change a little slower.
There will be a sharp cut-off in snowfall amounts south of the Tri-Cities, just off the edge of my snowfall map above, which will be south of the main isentropic lifting region ( where moisture is being transported up the sloping edge of retreating arctic air ).
A better idea of snowfall totals for this event will be had when the first 6-hour snow measurements are made by around 9:00 to 10:00 PM tonight.