SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1158 PM CST Sat Nov 14 2020

Valid 151200Z - 161200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL APPALACHIANS AND MID-ATLANTIC...

...SUMMARY...
Thunderstorms associated with strong wind gusts will be possible
this afternoon and evening across parts of the central Appalachians
and Mid-Atlantic.

...Central Appalachians/Mid-Atlantic...
An upper-level trough will move quickly east-northeastward across
the southern Great Lakes region today. The system will become
negatively tilted as a band of strong large-scale ascent moves into
the central Appalachians. At the surface, a cold front will advance
eastward into the central Appalachians with a pre-frontal trough
developing ahead of the front. Thunderstorms will likely be ongoing
along the pre-frontal trough at the start of the period across the
Ohio and Tennessee Valleys. This line will move quickly eastward
into the central Appalachians by midday. Ahead of the line, a
corridor of maximized low-level moisture will exist with surface
dewpoints mainly in the 50s F. This will be enough for weak
destabilization ahead of the line. By afternoon, RAP forecast
soundings have peak instability reaching the 200 to 400 J/kg range.
This combined with extreme deep-layer shear of 100 to 110 kt and 40
to 50 kt winds just above the surface, should enable a fine line to
develop. The fine line is expected to quickly move across the
Appalachian crest eastward into the foothills and coastal areas
during the late afternoon and early evening. Isolated damaging wind
gusts will be possible with this line of storms. A marginal risk has
been introduced in this outlook for much of Pennsylvania, Maryland
and northern Virginia extending eastward to the Mid-Atlantic coast.

..Broyles/Squitieri.. 11/15/2020

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