Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Aug 30 2024 20:15:03

AWUS01 KWNH 302014
FFGMPD
ILZ000-MOZ000-ARZ000-OKZ000-KSZ000-310230-

Mesoscale Precipitation Discussion 0953
NWS Weather Prediction Center College Park MD
413 PM EDT Fri Aug 30 2024

Areas affected...much of MO/IL...adjacent portions of KS/OK/AR

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

Valid 302030Z - 310230Z

Summary...Developing convection with 1-2"/hr rainfall rates may
repeat/train locally to result in 3"+ isolated totals. Localized
instances of flash flooding are possible.

Discussion...A slow moving cold front is providing a focus for
convective development late this afternoon over the Middle MS
River Valley, as small showers are already resulting in
isolated/localized downpours with rainfall rates of 1-2"/hr (per
MRMS estimates). The mesoscale environment is characterized by a
corridor of higher instability (SB CAPE 2500-4500 J/kg),
anomalously high tropospheric moisture (PWATs of 1.6-2.0 inches,
between the 90th percentile and max moving average, per SGF and
ILX sounding climatology), and effective bulk shear of less than
20 kts. Given a distinct lack of upper-level catalyst and
associated shear to organize/sustain convection, any resulting
flash flooding from 1-2"/hr rates will likely remain localized
(and largely confined to where these rates are able to locally
train/repeat).

While the HRRR is among the driest of the hi-res CAMs, the 12z
HREF has meaningful signal (30-60%) for localized 3"+ totals
through 03z (per 40-km neighborhood probabilities for 3"
exceedance). These totals are most likely in the vicinity of the
front itself, from northeast OK through MO/IL, though more common
average totals will be closer to 1" (per Ensemble Agreement Scale,
EAS post processing of the 12z HREF QPF, which indicates only
modest spatial agreement in 1" exceedance, indicated by relatively
low probabilities of 10-30%). Given the aforementioned lack of
shear and resulting convective organization, this makes sense, as
any individual downdraft should remain small and short-lived, so
only isolated/localized instances of flash flooding are considered
possible. Low-lying areas with poor drainage will be the most
susceptible to flood impacts, particularly if 3"+ totals occur in
a metropolitan area.

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7jszu9pFItQoPYXp20JMfAcbiCAdYtbzakGRzaxTnmOoOf8BYWz9GeGGBGPE36s2MtiH=
dWgVfTngt-kCFUvLzorgioU$  for graphic product...

ATTN...WFO...EAX...ICT...ILX...LOT...LSX...LZK...PAH...SGF...
TSA...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC...

LAT...LON   40808887 40678846 40058836 38578869 37619040=20
            36839159 36379309 36149439 36229593 36979565=20
            38079424 39039265 39849127 40528994=20

=3D =3D =3D
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