Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Jul 19 2025 07:37:33

AWUS01 KWNH 190737
FFGMPD
MNZ000-IAZ000-NEZ000-SDZ000-191300-

Mesoscale Precipitation Discussion 0754
NWS Weather Prediction Center College Park MD
336 AM EDT Sat Jul 19 2025

Areas affected...much of IA...far southern MN...far southeastern
SD...northeastern NE

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

Valid 190735Z - 191300Z

Summary...Localized training of 1-3"/hr rainfall rates likely to
result in short-term (3-hr) localized totals of 3-5" and isolated
to scattered instances of flash flooding.

Discussion...Coverage of deep convection has gradually increased
overnight, mainly along a WSW-ENE oriented axis of moisture
convergence from southeast SD though southern MN and northern IA.
This growing mesoscale convective system (MCS) exists within a
very favorable environment organized convection and heavy
rainfall, as characterized by plentiful instability (1000-3000
J/kg of ML CAPE, having increased 200-600+ J/kg over past 6-hr
across IA and surroundings), anomalously high tropospheric
moisture (PWs 1.6-1.9", near or above the 90th percentile per OAX
sounding climatology), and effective bulk shear of 30-40 kts. As
low-level moisture transport/convergence peaks over the next
several hours (with idealized southwesterly upglide along 300-305
K isentropic surface through 12z), upper-level divergence (via
favorable right-entrance region of ~100 kt jet streak @ 250 mb
over northern WI) should support continued upscale growth of the
convective system (per MCS maintenance probabilities of 40-70%).
This will result in a period of heightened flash flood concerns
towards dawn, as the veering LLJ is expected to result in
localized training through 12z in the vicinity of central and
northern IA.

Expect rainfall rates of up to 1-3"/hr to continue into the early
morning with localized training segments likely resulting in
short-term (~3-hr) localized totals of 3-5" (with corresponding
Flash Flood Guidance of only ~2.0"). While some of the latest HRRR
runs have backed off on depicting totals like this, many earlier
runs did show these amounts (along with more consistent runs of
the experimental RRFS) with 00z HREF 3" exceedance probs of up to
30% as well. Isolated to scattered instances of flash flooding are
likely.

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!__Eul0iaYZIghNVkYkpO1QM8_NIAxN_bOe2Wp0JeSEvSXNqaNTSjIw6cE-t1cKl3_7MU=
0HU6Ywoc6eNhAb16zk_H9Cc$  for graphic product...

ATTN...WFO...ARX...DMX...DVN...FSD...LBF...MPX...OAX...

ATTN...RFC...KRF...MSR...NWC...

LAT...LON   44079334 43629177 42669117 41459105 40949275=20
            41279453 41589584 41669688 41939846 42589922=20
            43539797 43699562=20

=3D =3D =3D
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