Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Jul 01 2023 06:44:51

AWUS01 KWNH 010644
FFGMPD
OHZ000-KYZ000-INZ000-ILZ000-011100-

Mesoscale Precipitation Discussion 0610
NWS Weather Prediction Center College Park MD
243 AM EDT Sat Jul 01 2023

Areas affected...Southern IL...North-Central KY

Concerning...Heavy rainfall...Flash flooding likely

Valid 010640Z - 011100Z

Summary...Localized repeating of 1-2"/hr rainfall rates over
already saturated soils are likely to lead to isolated to widely
scattered instances of flash flooding.

Discussion...Semi-discrete (but widely scattered) convection has
been ongoing across much of the Ohio Valley overnight, but has
recently become a bit more organized across southern IN into
portions of northern KY. A traversing shortwave trough (with the
base currently located near central OH) is likely helping to
provide some broad ascent, though an indirect enhancement of the
low-level jet locally (to 25-30 kts at 850 mb) may end up being
the more impactful factor of the shortwave (providing moderate to
strong moisture transport, with some additional strengthening of
the LLJ expected still). The mesoscale enviornment in the vicinity
of the organized convection is characterized by ample instability
(MU CAPE 1500-3000 J/kg), PWATs of 1.7-1.9 inches (above the 90th
percentile and nearing the max moving average, per ILN sounding
climatology), and effective bulk shear of 30-40 kts. The
southwesterly trajectory of the LLJ is helping to drive storm
motions towards the south of the mean 850-300 mb flow (which is
directed towards the east-southeast), per the upwind propagation
vector. This is already beginning to favor a bit of a training
axis, and 1-2"/hr rates are likely to repeat locally over some
locations (before likely pivoting south and eventually weakening).

While hi-res CAM guidance has been particularly bad at depicting
ongoing convective activity (with the ARW and ARW2 being the only
HREF members with meaningful QPF near the correct area), the 40-km
neighborhood exceedance probabilities for the 3" threshold are
still as high as 20% through 12z (though probably a bit underdone
and notably offset too far northeast). These amounts will likely
fall in a relatively short period (3 hours or less), with most of
the region having a corresponding Flash Flood Guidance (FFG) of
only 2". Indeed, a good portion of the MPD area has seen 1-3" of
rainfall over the past couple of days (with a smaller strip of
3-6" totals across far southwest IN), so the relatively low FFGs
seem to make sense. Given the wet antecedent conditions and
observational trends, isolated to widely scattered instances of
flash flooding are considered likely.

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_HtzEuEEPeVSqVqecUjcIOJryApm4rrqhaIt7-krV3XBAy656FX95ddhDgW6f7udvTUb=
-0olPRTNzMcWIux6APCcGlE$  for graphic product...

ATTN...WFO...ILN...ILX...IND...JKL...LMK...PAH...

ATTN...RFC...OHRFC...NWC...

LAT...LON   39678683 39648486 38778367 37568392 36958538=20
            37048718 38518825=20

=3D =3D =3D
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