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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