ALERT For Accumulating Snow Overnight Into This Morning Along The Upslope Side Of The Mountains. Caution For Hazardous Road Conditions Along and North of High Knob Massif-Tennessee Valley Divide.
A period of increased low-level moisture will develop overnight with snow showers and local squalls increasing along the upslope side of the mountains ( with respect to NW winds ). At 11:00 PM a burst of snow had moved through Breaks Interstate Park.
Additional new accumulations of 0.5″ to 2″ are expected at lower and middle elevations, with 2″ to 3″ within upper elevations of the High Knob Massif. Little to no accumulation, as has been expected, will occur along the downslope side of the mountains ( this ALERT has always been posted for the upslope side of the mountains with respect to NW winds ).
Overnight Into Mid-Morning Friday
Snow showers & flurries. Snow may be heavy at times in the overnight-sunrise period. W to NW winds 10-20 mph, with higher gusts. Temperatures varying from the low-mid 10s at highest elevations to the mid-upper 20s ( milder at lower elevations toward the Tri-Cities ). Wind chill factors varying from single digits below & above zero at the upper elevations to the 10s to lower 20s. Blowing snow, with additional rime formation, at highest elevations.
Mid-Morning Through This Afternoon
Mostly cloudy & cold. Chance of flurries or snow showers. W-NW winds 5-15 mph, with higher gusts. Temperatures varying from lower 20s to lower-mid 30s ( coldest at the highest elevations ). Wind chills in the 10s & 20s, except some single digits at highest elevations.
Tonight Into Saturday Morning
Mostly cloudy & cold. Chance of flurries. W-WSW winds at 5-15 mph, with higher gusts, along mid to upper elevation mountain ridges. Temperatures mostly in the 20s, varying from around 20 degrees at highest elevation to around 30 degrees. Wind chills in the 10s & 20s, except some single digits along upper elevation mountain ridges.
Weather Discussion ( February 25-26 )
My Afternoon Discussion
Its been a cold day across the mountain area with 4:00 PM temperatures varying from a bitter 20 degrees atop Eagle Knob of the High Knob Massif to 31 degrees ( 30.6 ) at the City of Norton Water Plant ( reported by Joe Carter ).
This followed an overnight that featured periods of heavy snow from the High Knob Massif northward into parts of Wise and Dickenson counties.
A general 0.5″ to 2.0″+ of new snow accumulated, enough to force Wise County to close schools on this TGIF ( Feb 26 ). No new snow accumulated in many downslope places, as well as in spots that happened to miss the overnight snowstreaks and squalls along upslope sides of the mountains ( e.g., only a trace in Grundy ).
Total snowfall during this event had reached 4.0″ in the High Chaparral community of the High Knob Massif up to 9:43 AM this morning. Look for scenes from the summit level and main crest zone coming later.
Snowfall was generally less in Norton-Wise and less still toward Pound and Clintwood where, with melting Thursday, some places barely had a dusting ( that missed overnight snow squalls ).
In general; however, it was clearly an elevation biased snow event featuring snowfall ranges along the upslope side of the mountains which varied from 1″ to 6″+ ( during the entire Feb 24-26 period ).
My Overnight Discussion
Light snow has been increasing, mixed with sleet in valleys, over Dickenson and Buchanan counties during the evening with a burst of heavier snow recently moving through the Breaks Interstate Park area. This marks the beginning of a return of better low-level moisture.
When forecasting Great Lake connected NW upslope flow, from this far away from the moisture source, it is all about being PATIENT and giving the moisture time to make the long trek downstream into the mountains.
Nothing had changed dramatically in the flow, as was expected, with a mostly mid-continental flow into the mountain area at 7:00 PM. That supported light snow.
Overnight models continue to show the flow shifting to off Lake Michigan into the mountains for a period of time from the overnight-predawn into mid-morning Friday. This will be the period for accumulating snow ( i.e., Midnight to Mid-Morning on Friday will be the best time ).
The only change in my forecast has been to reduce snowfall amounts slightly due to sleet mixing in at lower elevations this evening within the Russell For Basin.
With Great Lake supported upslope flow upstream radars may not look very active, but echoes increase along the mountains as moisture reaches the lifting zone.
Streamers are clearly visible coming off Lake Michigan, indicating that moisture is being transported off the open Lake. Little is seen beyond the immediate inland Lake zone in Michigan-Indiana until the air reaches the Appalachian foothills in Kentucky & western West Virginia ( with additional lifting then into the Alleghenies and Cumberland mountains ).
One reason I have not backed off on overnight snowfall is that there is also to be a 10 degree temperature drop at the summit level of the High Knob Massif, and in many places, with arrival of the 850 MB thermal MIN and coldest air that will help promote increased dendritic crystal growth at a lower altitude in the atmosphere ( even though the most prime growth zone of -12 to -17 C is not quite going to be reached there should still be some decent crystal growth ).
So time will tell. One of the problems in dealing with Great Lake moisture is that only a few degrees of change on the compass can make for large changes downstream at distances of 400 air miles, and models have a difficult time resolving these streams of richer low-level moisture with respect to where they will exactly form and reach over time.
*The distance from the end of Lake Michigan to the High Knob Massif is approximately 400 air miles.
Whitewater continues to gush as part of a prolonged period with significant flow on the dozens of steep creeks draining the High Knob Massif ( a testimony to February and Winter wetness in this 2015-16 season ).