040716 Forecast

My Forecast For Today ( April 7 )

A prolonged period of cold conditions is expected from Thursday night into this weekend.  Rain and snow showers will be possible Thursday night into Friday, with the best chance for snow by late Friday into Saturday AM.  The potential for several inches of snow will exist in upper elevations, especially above 3300 feet, with a general decrease in sticking as elevation decreases below 3000 to 3300 feet ( a little sticking will be possible to around 1500-2000 feet, on the upslope side of the mountains, by Saturday AM ).

Late Evening Into This Morning

Rain with a chance for thunder.  Locally heavy rainfall.  A break in rain by the predawn-sunrise period.  Winds SSW-W at 10 to 25 mph, with higher gusts, decreasing some toward morning.  Temperatures dropping into the 40s, with 30s at highest elevations.  Wind chills in the 20s & 30s.

Mid-Morning Through This Afternoon

Showers redeveloping.  SW-W winds 10-25 mph, with  higher gusts, along middle-upper elevation mountain ridges & plateaus.  Chilly.  Temperatures varying from 30s at upper elevations to the 40s to lower 50s ( milder south toward the Tri-Cities ).  Becoming partly cloudy by mid-late afternoon or early evening.  Wind chill factors in the 30s and 40s ( coldest at highest elevations ).

Tonight Into Friday Morning

Partly to mostly cloudy.  Chance for rain or snow showers.  Turning colder.  WNW winds 5-15 mph, with higher gusts.  Temperatures dropping into the 30s, with 20s above 3200 feet in elevation.  Wind chills in the 10s & 20s ( coldest at highest elevations ).


Weather Discussion ( April 6-7 )

Increasing clouds & gusty conditions Wednesday developed in wake of a frosty cold morning in mountain valleys.  A 41 degree temperature spread was observed in Clintwood from  24 degrees in the morning to 65 degrees in the afternoon.

Nora 4 SSE - NWS Site In Middle Elevations
Nora 4 SSE – NWS Site In Middle Elevations ( Elevation 2650 feet )
A more “narrow” temperature spread was observed along exposed mountain ridges and plateaus, with readings varying from the 30s into the 50s ( only upper 40s to about 50 degrees at the summit level of the High Knob Massif ).
JKL Doppler At 11:51 PM - Thursday ( April 6, 2016 )
JKL Doppler At 11:51 PM – Thursday ( April 6, 2016 )

The focus tonight is on needed rain, with brief downpours in places, that is moving across the mountains ahead of the first of two cold fronts ( with initially dry air in place, some evaporation occurred to make totals at the ground less than estimated by Doppler radar up to midnight ).

Black Mountain MesoNET Up To 1:00 AM Thursday
Black Mountain MesoNET Up To 1:00 AM Thursday – April 7, 2016
It is a wind driven, cold rain along high mountain crest lines with recent gusts between 40-50 mph ( driving wind chills into 20s ).
USA Water Vapor Image At 12:15 AM Thursday - April 7, 2016
USA Water Vapor Image At 12:15 AM Thursday – April 7, 2016

A trough visible in the upper air over the eastern USA will deepen during the next couple of days, with anomalously cold air for this time of year spilling south over the region.

European Model 850 MB TEMP Anomalies-Wind Vector
European Model 850 MB TEMP Anomalies-Wind Vector Forecast – 8 AM Saturday

Cold air transport reaches its maximum Friday Night into Saturday, with a NW flow pattern that will also help carry enough moisture south from open Great Lake waters to support some spring snowfall.

NAM Model 500 MB Vorticity Forecast
NAM Model 500 MB Vorticity Forecast At 2:00 PM Friday – April 8, 2016

Diffluence ( upper air divergence ) ahead of an approaching vorticity maximum diving toward the base of the upper air trough will begin to generate lower elevation rain showers and upper elevation snow showers during Friday afternoon, with increasing snow showers into Friday Night when snow levels will begin dropping toward the middle elevations.

At the current time, best accumulations are expected above 3300 feet in elevation with decreased sticking as elevation decreases below this level.  There will be a period of time ( generally from midnight-sunrise Saturday ) when snow levels could reach down into the 1500-2000 foot zone for locations along the upslope side of the Cumberland Mountains ( with respect to NW flow ).  Snow amounts are expected to be limited for most places by duration of these best conditions for snowfall ( best sticking being on above ground objects, grass, leaves, and northern slopes outside of the highest elevations ).  Please stay tuned for updates.
The coldest air is expected along mountains ridges into Saturday morning, with coldest air in mountain valleys likely into Sunday morning.  Prolonged below freezing conditions are expected in all locations, with anomalously cold wind chills across higher terrain locations during Friday night into Saturday.

Have a great Thursday.