Mesoscale Discussion 1442
NWS Storm Prediction Center Norman OK
1038 AM CDT Fri Aug 04 2017
Areas affected...Much of the upper Ohio Valley
Concerning...Severe potential...Watch possible
Valid 041538Z - 041745Z
Probability of Watch Issuance...40 percent
SUMMARY...Severe hail/wind risk with increasing thunderstorm
development may remain somewhat localized and/or sparse in coverage
through early to mid afternoon. However, potential does exist for a
slow increase in coverage and organization which could be
accompanied by a more substantive risk for damaging wind gusts later
this afternoon. Trends will continue to be monitored for the
possibility of a watch.
DISCUSSION...Weak to moderate pre-cold frontal destabilization is
now underway across much of the upper Ohio Valley, primarily as
insolation contributes to warming of a seasonably moist boundary
layer. Latest objective analysis suggests that inhibition is
already becoming increasingly negligible, particularly within a
corridor ahead of the front, from parts of north central Kentucky
through the Lake Erie area. Aided by large-scale ascent ahead of a
significant short wave trough now pivoting eastward toward the lower
Great Lakes/upper Ohio Valley region, a general increase in
thunderstorm activity appears likely through 17-20Z.
Further daytime heating may yield CAPE as high as 1500-2000 J/kg,
supportive of vigorous updrafts. However, warm sector southwesterly
deep layer mean flow, even with some strengthening, appears likely
to remain on the order of 30-35 kt. And models indicate that the
mid-level cold core of the approaching system will lag to the west.
Still, weak cooling aloft may be enough to support some risk for
marginally severe hail in initial stronger pulsing activity.
Vertical shear and instability may become marginally sufficient to
support a gradual increase in convective organization, which may
eventually be accompanied by an increasing risk for potentially
damaging wind gusts. This probably will take some time through,
with any severe hail/wind risk expected to initially remain fairly
sparse in coverage.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 41348239 42558078 43027834 41277821 38218133 37858388