Day 1 Severe Weather Outlook

Valid 131300Z – 141200Z


A few severe thunderstorms with damaging winds are expected from
southeast Lower Michigan into northern Ohio this afternoon.

…Southeast Lower MI into IN/OH this afternoon/evening…
A midlevel low over northern MN is evolving into an open wave while
moving northeastward towards James Bay, as embedded speed maxima
rotate around the southeastern periphery of the low. At the
surface, a cold front will progress eastward across IN/Lower MI
during the day, and the warm sector will spread northeastward into
southeast Lower MI ahead of the front. A corridor of surface
heating is expected from IN/OH into southeast Lower MI, to the
southeast of the thicker clouds associated with ongoing
(pre-frontal) convection from northeast IL to central Lower MI.

Midlevel lapse rates will remain rather modest (less than 7 C/km)
within the warm sector today. Still, surface temperatures warming
to near 80 F in southeast Lower MI and well into the 80s across
IN/OH, in combination with 68-70 F boundary-layer dewpoints, will
result in MLCAPE of 1000-1500 J/kg. Storms are expected to form by
early afternoon from northeast IN into southeast Lower MI, and then
continue eastward across northern OH into this evening. Diurnal
destabilization will coincide with an increase in midlevel
flow/vertical shear, which will support both organized storm
clusters/supercells along the cold front with a primary threat for
damaging winds. A low-end tornado threat is expected from southeast
Lower MI into northern OH where low-level shear/hodograph curvature
will be greater near the surface warm front this afternoon/evening.
The severe threat will diminish to the south in conjunction with
weakening vertical shear.

…Western NC into SC this afternoon…
Strong surface heating and lingering low-level moisture along and
southwest of a reinforcing frontal surge could provide some focus
for thunderstorm development this afternoon. Thermodynamic profiles
will favor some potential for isolated damaging downbursts given
DCAPE values near 1000 J/kg.

…Southeast FL coast today…
Convection with gusty winds will be possible along the southeast FL
coast, where northeasterly low-level winds will increase to about 30
kt around the northwest periphery of a tropical disturbance near the
southeast Bahamas. Moist profiles, however, should limit the
potential stronger/damaging outflow winds.

..Thompson/Gleason.. 09/13/2019


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