Issued earlier , but goes until 9pm or so
0951
NWS Weather Prediction Center College Park MD
331 PM EDT Mon Sep 05 2022
Areas affected...Portions of the Lower and Middle OH Valley
Concerning...Heavy rainfall...Flash flooding possible
Valid 051930Z - 060130Z
SUMMARY...Locally slow-moving showers and thunderstorms are
expected to pose a threat for a few instances of flash flooding
heading into the evening hours.
DISCUSSION...An elongated and broad mid-level trough and
associated closed low stretching through the middle MS and
lower/middle OH Valley region continues to help focus a
quasi-stationary front across the region with multiple weak waves
of low pressure advancing northeast along it. Sufficient diurnal
heating has ensued over the last several hours to help drive
moderate instability in the boundary layer in vicinity of the
front, and the latest RAP analysis shows an axis of MLCAPE
reaching 1000 to 1500 j/kg. GOES-16 visible satellite imagery does
show an expansive area of moderate CU and TCU across the region
which is reflective of the unstable boundary layer.
Broad diffluence aloft with embedded vorts in the southwest
mid-level flow coupled with the instability and presence of a
tropical airmass in the lower levels of the column should result
in some gradual expansion of showers and thunderstorms over the
next few hours. The activity will tend to be scattered in nature,
but may tend to be locally focused and slow-moving near the
aforementioned front where somewhat stronger low-level
forcing/convergence will be noted. Convection in time is expected
to also build a bit deeper into the warm sector south of the front.
Expect rainfall rates to locally be as high as 2 inches/hour and
some storm total amounts through mid-evening may reach upwards of
3 to 4 inches. This is consistent with the 12Z HREF suite of
guidance. A few instances of flash flooding will be possible given
the high rainfall rates, and generally the more sensitive urban
areas will be most prone to runoff concerns
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