Day 1 Severe Weather Outlook

Valid 181630Z – 191200Z


The main severe-thunderstorm threat today will be damaging winds
from Illinois into eastern Lower Michigan.

…Great Lakes to the Ozarks this afternoon…
A northern stream shortwave trough will progress eastward from
northern MN across the upper Great Lakes, as midlevel heights begin
to rise over the southern Plains. In advance of the northern stream
trough, multiple remnant MCVs now from MO to WI will move eastward
to IL and Lower MI during the afternoon. Ongoing convection in
Lower MI has weakened slowly the past couple of hours. Some
strengthening is possible early this afternoon along the leading
edge of the outflow into eastern Lower MI as the low levels
destabilize with surface heating, though confidence is not
particularly high. Larger buoyancy will reside farther south into
IN/IL where boundary-layer dewpoints in the low 70s persist beneath
the eastern extent of an elevated mixed layer. Convective
inhibition will weaken as surface temperatures warm into the upper
80s to lower 90s this afternoon, and new thunderstorm development is
expected along the remnant outflow boundaries from MO into IL/IN.
Rather modest vertical shear with up to 40 kt midlevel flow will
generally favor multicell clusters with damaging winds, though
midlevel lapse rates will be sufficiently steep for some hail

Storm development is a little less certain from southern MO into
eastern OK, given the ongoing midlevel convection and persistent
clouds. There is some potential for development this afternoon in
the differential heating zone near the southern influence of the MCV
over MO. Some warm advection will persist into this evening a bit
farther to the northwest, though storm evolution/intensity is still
in question.

…NY/PA this afternoon…
A weak midlevel trough will move east-northeastward from the lower
Great Lakes across NY/PA this afternoon. A broken band of storms
now forming in northwest PA is likely the precursor to a loose band
of storms that will persist through the afternoon and spread into
NY. Multicell clusters and/or low-end supercell structures will
pose some threat for damaging gusts this afternoon.

..Thompson/Elliott.. 08/18/2019


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