Day 1 Severe Weather Outlook

Valid 121200Z – 131200Z


Scattered severe thunderstorms are expected across portions of the
mid/upper Mississippi Valley. More isolated activity is expected to
extend across eastern Kansas into the Texas South Plains. A few
strong storms are also possible across the Middle Atlantic region.

…Mid/Upper MS Valley…

Strong short-wave trough is forecast to eject across WY/CO early
this morning before shifting into the Dakotas/central Plains by 18z.
Associated 500mb speed max, on the order of 70kt, will translate
into southeast SD by early afternoon then progress into western IA
by 13/00z. This feature is partly responsible for an MCS over SD/NE
at 0530z which is expected to propagate across eastern NE into
western IA by morning. Models are in general agreement this activity
should gradually weaken as LLJ veers and weakens by sunrise.
However, there is some concern the MCS could be potentially more
disruptive to a reservoir of buoyancy across the mid MS Valley. If
this occurs then severe probs may need to be adjusted at 13z to
reflect the airmass modification.

Latest thinking is strong large-scale forcing for ascent will spread
across the eastern Dakotas/NE into MN/IA during the afternoon hours.
Substantial height falls are expected across this region, and
barring a disruptive MCS continuing beyond sunrise, downstream
surface front should advance north across northern IA into southern
MN before stalling ahead of the short wave. If boundary layer
recovers, as expected, discrete supercells should evolve along/south
of the NW/SE-oriented surface boundary over southern MN/northeast
IA. Expected wind profiles favor at least some threat for a few
tornadoes. Otherwise, damaging winds and some hail can be expected.

…Central/Southern Plains…

While large-scale height falls will be limited to areas north of
I-70, notable surface front is surging south across the High Plains
and should extend across eastern KS-northwest OK-TX Panhandle by mid
afternoon. Surface readings should soar through the upper 80s to
near 90F ahead of the boundary and convective temperatures should be
breached by 20-21z. Seasonally high-PW air mass and frontal lift
should easily contribute to scattered thunderstorms along the
trailing boundary. This activity should grow upscale as it
propagates slowly southeast during the evening. Locally damaging
winds are the primary severe threat.

…Middle Atlantic…

Strong boundary-layer heating is forecast across portions of the
Middle Atlantic region, especially from southern NJ into the
Carolinas. As temperatures climb through the mid 80s to near 90F,
scattered deep convection is expected to develop, both along the lee
trough and more pronounced cold front over NJ/PA. Wind profiles are
not particularly strong but northwesterly deep-layer flow should be
adequate for multicell clusters capable of generating locally strong
wind gusts. This activity should propagate toward southeast VA/NC
during the evening hours.

..Darrow/Squitieri.. 09/12/2019


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