Day 1 Severe Weather Outlook

Valid 271300Z – 281200Z


Some severe threat can be expected with thunderstorms across the
southern Mid-Atlantic states. Damaging winds are the primary threat,
although a brief tornado cannot be ruled out.

…Southern Mid-Atlantic through late afternoon…
A midlevel shortwave trough over Lower MI/OH this morning will
continue east-northeastward over PA/NY today and reach New England
this evening. An associated surface cold front will likewise move
eastward across the Appalachians and reach the Mid-Atlantic coast
tonight. Low-level moisture will spread northward in advance of the
front today, with boundary-layer dewpoints expected to range from
the upper 60s across the Delmarva to lower 70s in NC, though
midlevel lapse rates will remain poor. Still, this moistening and
surface heating in cloud breaks will contribute to weak
destabilization (MLCAPE near 500 J/kg) into the Delmarva today, with
MLCAPE of 1000 J/kg or greater to the south into NC.

The stronger forcing for ascent will skirt the north edge of the
surface warm sector through about 18z, with gradual height rises
expected over VA beginning by mid afternoon. Deep-layer and
low-level vertical shear will weaken with southward extent through
the afternoon, leaving mid morning to mid afternoon as the primary
window for damaging gusts and a brief tornado with a forced band of
convection along the front across eastern PA/NJ into eastern VA.
Farther south into NC, a few storms may form late afternoon along
the front when buoyancy will be maximized, but low-level flow/shear
will tend to weaken through the afternoon. Overall, the poor lapse
rates and lack of phasing of the ascent and vertical shear with the
more unstable warm sector all suggest that the damaging wind threat
is, at best, a low-end Slight risk.

..Thompson/Smith.. 10/27/2019


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