704
AWUS01 KWNH 180145
FFGMPD
WIZ000-ILZ000-MNZ000-IAZ000-180600-

Mesoscale Precipitation Discussion 0952
NWS Weather Prediction Center College Park MD
944 PM EDT Sun Aug 17 2025

Areas affected...south-central/southeastern MN into
north-central/northeastern IA and adjacent portions of WI/IL

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

Valid 180140Z - 180600Z

Summary...1-3"/hr rainfall rates to continue into the overnight,
resulting in localized short-term rainfall totals as high as 4-8".
Scattered to numerous instances of flash flooding likely, some
significant/life threatening (particularly across south-central
and southeastern MN).

Discussion...Convection is proliferating this evening in the
vicinity of a low-level frontal zone and associated
instability/thetaE gradient, extending from southwestern MN
through northeastern IA into northern IL. A weak shortwave/vort
max immediately upstream (ND/SD/MN border region) seems to be
resulting in the most intense/widespread convection across
south-central MN into north-central IA (by way of DPVA and added
divergence aloft from the right-entrance region of an associated
jet streak), and this convective organization should continue into
the early overnight hours as the low-level jet strengthens. The
mesoscale environment is otherwise characterized by an MLCAPE
gradient of 2500-4500 J/kg (with +400 J/kg in the past 3-hr over
southern MN), precipitable water of 1.6-2.0" (well above the 90th
percentile and approaching the max moving average, per MPX
sounding climatology), and effective bulk shear of 25-30 kts.

While observational trends favor portions of south-central and
southeastern MN for the greatest coverage and intensity of heavy
rainfall in the near term, the hi-res CAMs (18z HREF and 12z
experimental REFS) strongest signal is displaced to the northwest
(clustered over central MN, which is where the best dynamics are
certainly located... but ultimately too far displaced from the
best boundary layer thermodynamics which the deep convection has
favored and anchored to). Despite this spatial displacement, the
signal suggests relatively high chances for localized 3"
exceedance (30-50% probs, per 40-km neighborhood of HREF/REFS).
Farther to the southeast along the frontal zone (where dynamics
are less impressive and training should be less of an issue, but
storm motions tend to be slower with storms still capable of
1-3"/hr rates) the CAMs still support the potential for 3"
exceedance (10-30% probs) with the more recent experimental WoFS
runs (23-01z) even suggesting the potential for localized totals
of 4-8" from south-central/southeastern MN into
northeastern/eastern IA (per 90th percentile QPF and associated 5"
exceedance probabilities of 40%+).

As much of the region remains fairly saturated from recent days
heavy rains (with an axis of 2-4" of rain across a portion of the
area over just the past 24-hr), Flash Flood Guidance (FFG) suggest
impacts from as little as 1.0-2.0" over 1-3 hour period. As a
result, scattered to numerous instances of flash flooding are
considered likely. Given the particular hydrologic sensitivity
across portions of southeastern MN (including the Twin Cities
metro area), there is a higher than typical risk for localized
instances of significant/life threatening flash flooding.

Churchill

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...ARX...DMX...DVN...FSD...ILX...LOT...MKX...MPX...

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

LAT...LON   45599402 45539299 44939193 44209097 43499030
            42648973 40878869 40488968 41449141 41969241
            42659378 43249509 44269503 45059471