021416 Forecast

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

Preliminary Snowfall Forecast For Sunday-Tuesday ( February 14-15, 2016 )
Preliminary Snowfall Forecast For Sunday-Tuesday ( February 14-15, 2016 )
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.

This Afternoon

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 ).
High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise

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.

Nora 4 SSE - Official NWS
Nora 4 SSE – Official NWS Site For Middle Elevations ( 2650 feet )
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.


My Overnight Discussion

Reference my 021316 Forecast discussion section for details on this past weather event, and a look at different model forecasts for the upcoming winter storm.

The main change to my forecast for tonight, which I made last night, is to drop MIN temperature well below zero for some of our mid-upper elevation mountain valleys which either have or have access to ( via cold air drainage ) deep snow which is helping to chill the air even more ( a general 6″ to 12″+ of snow depth is currently across northern slopes and high valley basins of the High Knob Massif, with lesser but still significant snow depths in other major mountain ranges of the area ).  I noted in my forecast last night that temps could become colder than I had if skies were clear.

Black Mountain MesoNET
Black Mountain MesoNET Up To Midnight on February 14, 2016
Temperatures are currently around 0 degrees atop high mountain crest lines, and it is easy to see how lofty valleys have gotten so cold tonight ( this process occurring throughout the year on many nights favorable for cold air drainage, with enhancement during times with significant snow covering the ground ).
Although Black Mountain lacks high valleys, the sprawling and adjacent High Knob Massif is full of basins with many high valleys that sit between 2700 & 3500 feet above sea level.  When air that is already around 0 degrees drains over deep snowpack into a basin capable of collecting and holding it until vertical build up allows for spillage of air farther downstream, it can get very cold and drop well below summit temperatures.
The funneling downstream into mid-elevation valleys, such as that in which the City of Norton, Ramsey, Tacoma, and Coeburn rest, also pools and chills upon open valley floors ( the air being generally a little “milder” than in upper elevation valleys since there is more natural compressional warming with descent down from 3000-4000+ foot crestlines ).  Some micro-climatology that I have learned over the years, and hope to expand with help of my friends at the University Of Virginia’s College At Wise.
*The descent of air from upper elevations straight into lower elevations below 1500 feet, for example, appears to undergo enough compressional warming to offset much of the cooling.  Valley towns such as Harlan and Pineville, for example, tend to be much milder in low elevations below Black Mountain in SE Kentucky than towns on the Virginia side of the stateline during many nights conducive for cold air drainage.

 Even here in Clintwood, at my official NWS station, the air temperature has dropped to 5 degrees over only 2″ of snow depth and a much more limited vertical drainage basin in comparison to places like the City of Norton-Tacoma area.  This is a bitter night regardless of your location, but mid to high valleys ( especially ) with snow cover will be coldest!

Regardless of the time of year, or the specific weather setting, there are nearly always significant differences between lower, middle, and upper elevations.  A major objective of this website being to help educate about these differences, and at the same time provide a useful resource for those who live, work, travel, and yes, play, amid these diverse elevation zones.

Focus now shifts to a major winter storm system.

NAM 12 KM Model Total Precipitation Forecast
NAM 12 KM Model Total Precipitation Forecast – Next 60-Hours

Regardless of how much snow falls, models have settled on this being a heavy precipitation event so the timing of the change from snow to mix-rain will be critical in dictating amounts where you live.

GFS Model Total Precipitation Forecast
GFS Model Total Precipitation Forecast Next 84-Hours
The European Model is predicting 1.70″ at the Wise gridpoint, same as the NAM Model above ( it predicts a total of 4″ of snow at 10:1 ).
Canadian Model Total Precipitation Forecast
Canadian Model Total Precipitation Forecast – Next 84-Hours

While models continue to agree on a heavy axis of precip along the western side of the Appalachians, precise snow amounts are still somewhat varied.

NAM 12 KM Model Total Snowfall Forecast
NAM 12 KM Model Total Snowfall Forecast – Next 60-Hours
NAM 4 KM Model Total Snowfall Forecast
NAM 4 KM Model Total Snowfall Forecast – Next 60-Hours
GFS Model Total Snowfall Forecast
GFS Model Total Snowfall Forecast – Next 84-Hours
Canadian Model Total Snowfall Forecast
Canadian Model Total Snowfall Forecast – Next 84-Hours

The average of 5 different models for the Wise gridpoint is 4.8″ of total snowfall.  The 51-Member European Ensemble group had a mean of just under 6″ for Wise on the 12z run, with a few outliers going as high as a foot or more.

There is concern for significant orographic enhancement amid the High Knob Massif, where heavy precipitation is favored in a pattern like this ( whether it be snow or rain ).  With 6-12″ snow depths currently, the snow will be deep upon change to mix-rain.  Will the snowpack be able to retain water enough to prevent major run-off.

That is another concern to be considered as this winter storm event unfolds ( by later Monday into Tuesday ).

*With luck, upper elevations will change back to snow to halt or slow run-off before it gets out of hand into early hours of Tuesday.

Check back for Sunday Updates.