Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jul 28 2023 23:27:17

AWUS01 KWNH 282327
FFGMPD
WIZ000-ILZ000-IAZ000-290356-

Mesoscale Precipitation Discussion 0804
NWS Weather Prediction Center College Park MD
726 PM EDT Fri Jul 28 2023

Areas affected...portions of eastern IA

Concerning...Heavy rainfall...Flash flooding possible

Valid 282326Z - 290356Z

Summary...Thunderstorms are moving slowly across northeast IA and
their storm motions in spots are nearly aligned.  Hourly rain
totals to 2.5" with local amounts to 5" are possible.

Discussion...An upper level shortwave moving across central MN and
southeast SD has led to a divergent environment aloft.  Showers
and thunderstorms have been developing, growing in number, and
showing slow east to southeast movement during the past hour and a
half, which in some posts is nearly aligned with their
orientation.  This is leading to an uptick in the hourly rain
estimates from radar.  Precipitable water values are 2-2.2" per
GPS data.  Neighborhood ML CAPE is quite high, 3000-5000 J/kg.=20
Effective bulk shear is 30-50 kts.

While the 18z HREF guidance has this activity taking off to the
southeast almost immediately, the storms haven't been around long
enough to develop a significant cold pool, and progressive
convection in southeast MN is pretty far upstream.  Nevertheless,
believe storms will pick up the pace to the east-southeast after
01z.  Even then, the convective pattern could show waves for a
time before bowing out as this degree of effective bulk shear and
CAPE favors such a convective evolution.  A combination of
embedded mesocyclones and cell training are expected to be the
main methods for heavy rainfall in this area.  As the 18z HREF has
the signal for heavy rainfall leaving IA by 04z, used that as a
horizon for this MPD.  Any heavy rain-related issues should be
confined to urban areas and isolated to widely scattered.

Roth

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7Y-ZBQqRFFo1zvnLHNbWZah7WBjMKaorUuk3BdUayZlwdLT9L7c4vbjbGC5l1GNuisyf=
uKWHrKo8xV-bsb7fM04wFME$  for graphic product...

ATTN...WFO...ARX...DMX...DVN...MKX...

ATTN...RFC...NCRFC...NWC...

LAT...LON   43289217 43039045 41738979 41369164 42229368=20
            43059351=20

=3D =3D =3D
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