Day 1 Severe Weather Outlook

Valid 211200Z – 221200Z


Severe thunderstorms are possible across parts of the northern Mid
Atlantic Coast states into New England today. Additional strong to
severe storms are possible in a corridor from the central Plains
into the lower Ohio Valley, and near the Rockies.

A relatively progressive upper pattern is anticipated across the
northern third of the CONUS with a pair of deep shortwave troughs
advancing eastward and amplified shortwave ridging between them. The
eastern shortwave trough is expected to move through the Upper Great
Lakes, central/eastern Ontario, and into southern Quebec while the
western shortwave trough moves through the Pacific Northwest into
the northern Rockies.

At the surface, a cold front currently extends from southeast CO
northeastward to a low centered near the IA/MN/WI border
intersection. A warm front then extends from that low eastward
across central Lower MI through northeast PA and central DE. The
cold front will likely remain in place through this afternoon before
then pushing southward/southeastward into the Lower OH Valley and
northern portions of the southern Plains. The eastern portion of the
warm front will gradually lift northward throughout the day, placing
a warm and moist air mass over much of New England by the late

…New England into the northern Mid-Atlantic…
While the vertical ascent and enhanced flow aloft with the shortwave
described in the synopsis will remain predominantly north of the
region, a low-amplitude, lead shortwave trough (currently moving
through the OH Valley) is expected to move into New England this
afternoon. Warm and unstable air mass will be in place ahead of this
shortwave, and the expectation is for multiple bands of convection
to move across the region this afternoon. Some modest strengthening
of the low-level flow (i.e. around 30-35 kt at 850 mb) is
anticipated ahead of this shortwave trough, lengthening hodographs
and contributing to 0-1 km SRH around 100-150 m2/s2. Overall, wind
profiles support occasional supercell structures within
predominantly linear multicells. Primary severe threat will be
damaging wind gusts but isolated hail and a tornado or two are also

Vertical shear and forcing for ascent decrease with southern extent,
but a warm, moist, and diurnally destabilized air mass will support
widely scattered to scattered thunderstorm development. Wet
downbursts capable of damaging wind gusts are possible within the
strongest storms.

…Central High Plains into the Central Plains
The MCS currently moving into the NE Panhandle is expected to
continue eastward, reaching central NE by 12Z this morning. Isolated
threat for hail and strong wind gusts will exist with this system as
it continues into eastern NE.

Later this afternoon, scattered thunderstorms are expected to
develop across KS along the front as it begins to push southward. A
deeply mixed air mass characterized by temperatures in the upper
90s/low 100s and dewpoints in the low/mid 60s is anticipated ahead
of the front. Given the amount of dry air entrainment expected and
the lack of stronger vertical shear, updrafts will likely be
short-lived. Even so, isolated strong wind gusts are possible. Hail
could occur within the strongest updrafts.

At the same time, thunderstorms are expected to develop along the
lee trough from south-central CO into central WY. Mid-level flow
here will be the same as areas farther east (across the central
Plains), but vertical shear will be stronger due to northeasterly
surface winds. A few supercells capable of large hail and/or strong
wind gusts are possible and a tornado cannot be completely ruled
out. Uncertainty regarding severe thunderstorm coverage precludes
higher probabilities with this outlook.

…Mid MS Valley into the Southern OH Valley…
Outflow from the MCS across NE this morning will likely move into
southern MO and western KY this afternoon. A very moist and buoyant
air mass will be in place, with dewpoints in the 70s and MLCAPE in
excess of 3000 J/kg. Vertical shear will be weak, limiting storm
persistence, but updrafts are expected to be strong enough to result
in water loading and a resulting threat for isolated strong/damaging
wind gusts.

..Mosier/Nauslar.. 08/21/2019


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