Day 1 Severe Weather Outlook

Valid 201630Z – 211200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH THIS
EVENING FROM THE UPPER OH VALLEY INTO THE NORTHEAST…THE DEEP
SOUTH…AND THE MIDDLE TX COAST…

…SUMMARY…
Isolated strong to severe storms capable of producing mainly wind
damage may occur across parts of the Ohio Valley into parts of the
Northeast, the Deep South, and the middle Texas coast through this
evening.

…Synopsis…
A 995mb surface low in southern QC will develop northeastward in
advance of an ejecting, low-amplitude shortwave trough over southern
Lower MI, and an upstream trough over ON/Lake Superior. The surface
warm sector will likewise spread northeastward today into NY/PA/NJ
ahead of a cold front that will cross the Appalachians this evening
into tonight. The cold front will also continue to move
southeastward across the OH/TN and lower MS Valleys through tonight.

…Upper OH Valley into the Northeast this afternoon/evening…
Forcing for ascent along and ahead of the cold front will not be
particularly strong from OH into PA/NY, given that the ejecting
low-amplitude trough will move quickly northeastward over the Saint
Lawrence Valley this afternoon. Buoyancy will be somewhat limited
by poor midlevel lapse rates, though horizontal advection should
result in boundary-layer dewpoints in the 58-62 F range by mid
afternoon from western/central NY southwestward into PA, with
afternoon surface temperatures generally in the 60s. The net result
will be MLCAPE of 250-500 J/kg. The core of stronger low-level
winds/shear will develop northeastward over New England in tandem
with the ejecting shortwave trough, supporting an environment with
long hodographs, effective bulk shear near 60 kt, and some low-level
hodograph curvature. The environment appears conditionally
favorable for low-topped supercells, though the vertical shear may
be too strong for the relatively weak buoyancy/poor lapse rates.
Thus, will maintain a low-end damaging wind threat through the
afternoon.

…Deep South this afternoon/evening…
Thunderstorms are ongoing along and to the cool side of the cold
front from south central into southeast TX, while convection farther
northeast into northern MS is focused along a diffuse outflow
boundary. There is a narrow window for organized/strong storms into
middle TN through about midday, prior to increasingly thick clouds
and convective overturning here and to the south. Otherwise,
convection will largely focus along the front/outflow, with the
collective boundary sagging southeastward as storms move
east-northeastward along and to the immediate cool side of the
boundary. Low-level shear will remain relatively weak in the warm
sector, and convection will gradually exhaust the lingering
northeast extent of the steeper midlevel lapse rates. In the
interim, isolated damaging gusts and/or marginally severe hail will
be possible.

…Middle TX coast this afternoon…
Lift along the slow-moving cold front will overcome the stronger cap
to the south, and a corridor of moderate buoyancy (MLCAPE near 1500
J/kg) and effective bulk shear near 40 kt will support the potential
for isolated supercells. Given the moderate buoyancy and relatively
steep midlevel lapse rates, the strongest storms could produce
isolated large hail and damaging gusts.

..Thompson/Wendt.. 03/20/2020

$$

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