641
AWUS01 KWNH 290033
FFGMPD
WIZ000-MNZ000-SDZ000-NDZ000-290600-

Mesoscale Precipitation Discussion 0545
NWS Weather Prediction Center College Park MD
832 PM EDT Sat Jun 28 2025

Areas affected...Southeast North Dakota, Northeast South Dakota,
Central Minnesota

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

Valid 290031Z - 290600Z

Summary...Showers and thunderstorms will grow rapidly this evening
and may congeal into an MCS during the next few hours. Rainfall
rates of 2+"/hr are likely, which could produce 2-4" of rain with
locally higher amounts through training. Flash flooding is
possible.

Discussion...The regional radar mosaic this evening shows two
distinct areas of convection rapidly growing across the Dakotas.
These storms are intensifying in response to an approaching cold
front from the west, which is being pushed eastward by an
accompanying shortwave embedded within weak troughing of otherwise
zonal flow. Forcing for ascent is beginning to intensify
downstream of this shortwave/front, aided by both the LFQ of a
modest jet streak pivoting into SD, and through low-level
convergence along the nose of an amplifying 850mb LLJ which has
been measured recently at KFSD VWP at 30 kts. This LLJ is
additionally transporting robust thermodynamics northward as
reflected by the SPC RAP analysis, which suggests that MUCAPE has
climbed above 4000 J/kg coincident with PWs of over 1.5 inches.
Together, this lift and favorable environment will combine to
cause an increase in convection through the evening.

There remains considerable spread in the CAMs for the evolution
this evening, causing somewhat lower than typical confidence in
the flash flood potential. However, as the LLJ ramps up towards 40
kts it will further replenish thermodynamics northward, while also
enhancing ascent as it increases above the mean flow causing
additional convergence into the warm sector ahead of the cold
front. This combined with the cold front moving steadily eastward,
and bulk shear rising to 30-35 kts, suggests hedging towards the
CAMs with the most widespread and aggressive simulated
reflectivity during the next few hours. This will support rainfall
rates of 2+"/hr that are suggested by 20-25% probabilities from
the HREF (which are likely too low due to model performance this
evening), with brief rainfall rates of 3-4"/hr likely as shown by
15-min HRRR rainfall of 0.75" to 1". Although individual cells,
and the potential MCS produced via upscale growth, should be
progressive, training will become increasingly likely as the MCS
trails an outflow boundary to its south upon which additional
storms will develop and then move east which is supported by
veering Corfidi vectors. Where this training occurs, rainfall
could be 2-4" with locally higher amounts.

These intense rain rates will be sufficient to produce rapid
runoff and isolated flash flooding. However, the antecedent
conditions are also supportive due to 10-day rainfall that is more
than 300% of normal causing 0-40cm soil moisture above the 98th
percentile. This suggests minimal infiltration capacity of the
soils, so that while the greatest risk for flash flooding will be
through training, any of these intense rain rates, even if
progressive, could quickly overwhelm the soils to produce impacts
tonight.


Weiss

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

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

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

LAT...LON   47379700 46979527 46629391 46259265 45879232
            45359251 44839287 44609354 44529363 44479505
            44709658 45299754 46059837 46499849 46999806