040717 Forecast

Mountain Area Forecast ( April 7-9 )

ALERT For Accumulating Snow Overnight Into Friday Morning At Elevations Above 2000 Feet – Significant Accumulations Are Expected At The Upper Elevations With Lesser Amounts Below 3000 Feet 

*Snow Depth Forecast Into Friday – April 7

Below 2000 Feet:  Little to no accumulation

2000 to 3000 Feet: Dusting to 2″

Above 3000 Feet:  2″ to 8″+

*The greatest snow amounts will occur at the highest elevations.  Forecast error potential ( +/- ) 1″ on the listed elevation ranges to imply 1″ to 3″ possible at 3000 feet elevation.
The level of accumulating snow ( 1-2″ at the summit level of the High Knob Massif as of 8:00 PM Thursday ) will drop downward toward 2000-2500 feet by Friday morning ( on the upslope side of the mountains ).  Conditions will begin to improve after 11:00 AM Friday at all elevations ( but will remain windy & cold ).
Rain and snow, or a rain-snow-sleet mixture is expected to occur at elevations below 2500 to 2000 feet, with little to no accumulations below 1500-2000 feet in elevation.

Overnight Into Mid-Morning Friday

Rain changing to wet snow above 2000 feet.  Sleet possible.  Sticking snow levels dropping toward 2000 to 2500 feet by morning.  Rain showers or a mix continuing at elevations below 1500-2000 feet.  Snow heavy at times, especially at higher elevations.  Windy.  Cold.  Winds WNW-NW at 15-30 mph, with higher gusts.  Temperatures varying from upper 20s to middle 30s to the upper 10s to middle 20s at highest elevations.  Wind chill factors varying from 10s to lower 20s to the single digits and 10s ( except near to below zero in stronger gusts at high elevations in the High Knob Massif ).  Blowing and drifting snow at the highest elevations.

Friday Afternoon

Partly cloudy.  Windy & unseasonably cold.  Winds WNW-NW at 10-20 mph, with higher gusts.  Temperatures varying from 30s in upper elevations to the 40s.  Wind chills in the 20s and 30s, except 10s in gusts at highest elevations.

Friday Night Into Saturday Morning

Mostly clear.  Cold.  Winds diminishing in deeper valleys.  NW winds 5 to 15 mph, with higher gusts, on mid-upper elevation mountain ridges.  Temperatures in the 20s to lower 30s, except 10s within upper elevation valleys that can decouple from boundary layer flow ( i.e., winds calm with drainage flow development ).

Saturday Afternoon

Partly sunny ( high clouds possible ).  Milder.  Light winds shifting W-SW at generally less than 10 mph.  Temps from 40s in upper elevations to the mid-upper 50s.

Saturday Night Into Sunday Morning

Mostly clear.  Large vertical temperature spread developing between colder valleys and milder ridges.  Light southerly winds at less than 10 mph on most mountain ridges.  Temps varying from 20s to lower 30s in valleys to 40s on exposed mountain ridges-plateaus ( 10s to lower 20s in colder high valleys of the High Knob Massif ).


Weather Discussion ( Elevation Snow )

As typical for early and late season events, snow has been elevation biased so far and is expected to continue that way into Friday; although, snow levels will be dropping toward 2000 to 2500 feet over time.

Eagle Knob of High Knob Massif At 5:16 PM Thursday – April 6, 2017

Snow began falling around mid-day at the summit level of the High Knob Massif, with enough to coat the grass ( and especially the woods ) by 5:00 PM.  A burst of heavier snow later brought amounts into the 1″ to 2″ range by 8:00 PM.

 As of 9:30 PM moderate to heavy snow was reported by Darlene Fields in High Chaparral, at 3300 feet, but it was still not sticking to the ground there ( it likely will begin soon ).  Therefore, even at elevations above 3000 feet a notable range in snow depths and amounts will occur as colder air does not begin to really pour in until after the Midnight hour ( i.e., overnight hours of Friday ).

Black Mountain Mesonet – Sample Hour Ending At 10:15 PM ( April 6 )
Note 0.10″ in the rain gauge at the Black Mountain Mesonet site from 9:50 to 10:15 PM with heavy snow; however, wind gusts of 40-50+ mph means that even with an alter wind shield the rain gauge can not begin to catch nearly all that fell.  Determining amounts at high elevations are going to be complicated by very strong winds + above freezing ground temperatures.
Black Mountain Mesonet – Sample Hour Ending At 9:30 PM Thursday ( April 6 )

Very strong NW winds, with gusts around 50 mph or locally greater at highest elevations, are a real factor at mid-upper elevations and will help enhance rain-snow amounts into the overnight-morning hours of Friday.

NAM 3 KM Model 850 MB Temp Forecast At Noon Friday – April 7, 2017

Conditions will begin to improve, with respect to snowfall, after the mid-morning to mid-day period Friday behind the 850 MB thermal MIN ( -6 to -7 Celsius centered on 11:00 AM ) which drops air temps into upper 10s to lower 20s atop the High Knob Massif & Beartown peaks in southwest Virginia.

*The problem for those living in middle elevations being that as the air turns colder and snow falls the moisture supply will begin to wane Friday, thus limiting accumulations along the mountain chain southwest of the eastern West Virginia highlands where the moisture connection will persist longer in time.

Cold nights will continue through this weekend, especially amid mountain valleys.  By Saturday night a large vertical temperature spread will develop between colder valleys and milder ridges.  Vertical temperature differences of 20-30+ degrees will become possible into Sunday morning.