846
AWUS01 KWNH 171857
FFGMPD
WIZ000-MNZ000-IAZ000-180035-

Mesoscale Precipitation Discussion 0140
NWS Weather Prediction Center College Park MD
256 PM EDT Thu Apr 17 2025

Areas affected...western IA/MN border into southern MN/western IA

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

Valid 171853Z - 180035Z

Summary...Isolated flash flooding may develop during the late
afternoon hours from far northwestern IA into southern MN and
western WI. Rainfall rates of 1-2 in/hr are expected with brief
training which could allow for some 2 to 3 inch totals through 01Z.

Discussion...18Z surface observations showed a surface low located
over west-central MN near BDH with a cold front trailing
southwestward into NE across the MO River and a warm front
extending south-southeastward in IA. Surface observations over
northwestern IA/southwestern MN have shown a dewpoint rise of ~20
degrees over the past 6 hours, owning to rapid low level moisture
transport via 30-40 kt of 850 mb winds present over IA/MN out
ahead of the cold front. The increase in low level moisture
combined with daytime heating has led to MLCAPE values of
1000-1500 J/kg via 18Z SPC mesoanalysis data.

Visible satellite and radar imagery showed convective initiation
has occurred along the warm front in Sibley County with convection
likely to expand in intensity and coverage through the remainder
of the afternoon in the warm sector as the surface low and
attendant cold front advance downstream. Clear skies on visible
imagery and continued low level moisture advection are likely to
increase instability from current values across downstream
locations along the MN/WI border through 00Z. The portion of the
cold front closest to the surface low will track eastward more
quickly than the portion over the MO Valley, which when combined
with pre-frontal convection, may allow for brief training of
storms from SW to NE. With any areas of training, the environment
is supportive of rainfall rates of 1-2 in/hr which may allow for
isolated 2-3 inch totals through 01Z. Despite dry antecedent
conditions, flash flood guidance values are only 1-2 inches per
hour and ~1.5 to 2.5 inches in 3 hours. Localized flash flooding
will be possible into the early evening but the greatest threat
will likely be with with any urban overlap of heavy rain.

Otto

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

ATTN...WFO...ARX...DLH...DMX...FSD...GRB...MPX...

ATTN...RFC...MBRFC...NCRFC...NWC...

LAT...LON   45939305 45839185 45299052 44738999 44139044
            43929128 43749264 43239439 43359620 44079631
            45299515