Day 1 Severe Weather Outlook

Valid 311300Z – 011200Z

…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO EARLY TONIGHT FOR NORTHERN NC INTO SOUTHERN PA…

…SUMMARY…
Severe thunderstorms capable of damaging winds and a few tornadoes
are expected mainly this afternoon into early tonight from the
Carolinas into the Mid-Atlantic.

…Mid-Atlantic to Carolinas this afternoon into early tonight…
An intense midlevel shortwave trough now over MO will accelerate
east-northeastward through tonight toward PA/NY, while taking on a
more neutral-to-negative tilt and peak 500 mb wind speeds exceeding
120 kt. Strong surface cyclogenesis is expected in advance of the
amplifying midlevel trough, with a cyclone moving from OH to the
lower Great Lakes this evening, and continuing into southwestern QC
by early Friday. South of the deepening cyclone, a strong cold
front will move eastward from the OH/TN Valleys across the
Appalachians this afternoon, reaching the Atlantic coast overnight.
The cold front will be the primary focus for severe thunderstorms
through this evening.

Northward advection of low-level moisture is underway across the
Carolinas/VA, where boundary-layer dewpoints range from mid 60s
north to the lower 70s south. Dewpoints in the 60s should reach as
far north as southern NY by late afternoon, though widespread
clouds/rain will limit surface heating with northward extent from
VA. Despite poor low-midlevel lapse rates, the moist low levels
will promote at least weak buoyancy rooted near the surface into PA.
Buoyancy will be a little greater to the south into VA and the
Carolinas, where richer low-level moisture and some surface heating
in cloud breaks will support MLCAPE of 1000-1500 J/kg. Within the
warm sector, vertical shear will increase through the day in
response to the approach and deepening of the midlevel
trough/surface cyclone. Long hodographs with effective bulk shear
of 50-60 kt are expected, and there will also be sufficient
low-level shear/hodograph curvature for rotating storms (effective
SRH of 300-500 m2/s2).

Strong linear forcing for ascent along the cold front will be the
primary focus for storm development, mainly east of the Appalachians
this afternoon/evening. The strong linear ascent will favor upscale
growth into a squall line, though strong deep-layer shear and enough
east component to storm motions may allow some embedded supercell
structures to persist. The weak buoyancy and very strong low-level
shear will favor damaging winds as the primary threat, though a few
tornadoes will also be possible with embedded supercell and
mesovortex structures this afternoon/evening.

..Thompson/Smith.. 10/31/2019

$$

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