Mesoscale Precipitation Discussion 0512
NWS Weather Prediction Center College Park MD
732 AM EDT Wed Jun 25 2025

Areas affected...eastern South Dakota, southern Minnesota, far
northern Iowa

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

Valid 251132Z - 251700Z

Summary...Showers and thunderstorms will steadily increase in
coverage through the morning, focusing along an elevated boundary.
Rainfall rates within the stronger convection will exceed 1"/hr,
which through training could produce locally more than 3" of rain
and instances of flash flooding.

Discussion...The GOES-E IR imagery this morning shows an expansive
area of cold clouds with continued cooling tops stretched from
western SD through MN and IA. These cooling tops are associated
with expanding showers and thunderstorms developing within
pronounced ascent in the RRQ of a strengthening upper jet streak
centered over Ontario, aided by both a shortwave lifting across SD
and potent isentropic lift as the 850mb LLJ of 20-25 kts lifts
northward over a surface warm front. Thermodynamics across the
region are favorable for heavy rain as reflected by SPC RAP
analyzed PWs of 1.5 to 1.8 inches, above the 90th percentile for
the date, and MUCAPE around 1000 J/kg. This is supporting
widespread rainfall rates of 0.5-1"/hr from regional radars, with
expanding heavy rainfall occurring primarily along the nose of the
LLJ/elevated 850mb boundary.

During the next several hours, a wave of low pressure developing
along the warm front across SD will help pinch the flow
downstream, helping to accelerate the LLJ to offset the typical
diurnal weakening of this feature. At the same time, the flow may
back more prominently to the SE, helping to funnel even more
intense thermodynamics into MN/SD (PWs over 2" coincident with
1000 J/kg MUCAPE). The high-res CAMs indicate that convection may
focus in two swaths - along the warm front itself - and then more
impressively aligned to the elevated front where moisture
confluence will be most intense and the enhanced ascent downstream
of the shortwave will focus. Across this area, Corfidi vectors
become aligned to the elevated front and sharply right of the mean
0-6km winds, suggesting an enhanced training threat. With rainfall
rates progged by the HREF and REFS to exceed 1"/hr (40-60%
chance), this training will result in an axis of rainfall of 2-3"
with locally higher amounts exceeding 4" as reflected by 6-hr
HREF/REFS probabilities and PMM.

Recent rainfall has been highly variable across this region as
shown by NASA Sport 0-40cm soil moisture that is only above normal
in some places, leading to FFG generally 1.5 to 3 inches in 3
hours. HREF exceedance probabilities are 20-30% for these
thresholds, indicating the increased risk for flash flood
instances this morning anywhere in the region. However, the
greatest risk will likely be in an east-west axis along the
elevated front from far northeast SD through eastern MN.

Weiss

ATTN...WFO...ABR...DLH...DMX...FGF...FSD...MPX...

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

LAT...LON   46129639 46039406 45659283 44799290 43829334
            43239408 42929503 42859656 43199746 43589811
            44289898 44799938 45449921 45919813