818
AWUS01 KWNH 182118
FFGMPD
MIZ000-WIZ000-ILZ000-MNZ000-IAZ000-190315-

Mesoscale Precipitation Discussion 1085
NWS Weather Prediction Center College Park MD
516 PM EDT Tue Aug 18 2026

Areas affected...Parts of the Upper Midwest and Great Lakes

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

Valid 182115Z - 190315Z

SUMMARY...Growing organized convection across parts of the Upper
Midwest and Great Lakes through this evening ahead of an
approaching cold front will have the potential to produce hourly
rainfall rates up to 2.5" on an isolated basis. Repeating rounds
of storms containing these rates could produce pockets of 2-4"
rainfall totals and lead to at least isolated flash flooding
concerns.

DISCUSSION...Latest 2100Z radar and satellite observations depict
increasing coverage of showers and thunderstorms both along and
ahead of an approaching cold front crossing from the eastern MI
U.P. to far southern MN, with a weak wave of flow pressure
analyzed over northeast MI and the central MI U.P.. Mean layer
winds ahead of this front are out of the west and nearly parallel
to the approaching frontal boundary for some areas, which provides
potential for training/backbuilding storms for pockets prior to
the FROPA. Instability remains sufficient with SBCAPE of 2000-3000
J/kg in the region and MLCAPE over 2000 J/kg (per SPC`s
mesoanalysis), with the greatest values over the inflow region of
IA and southern MN. PWs are also supportive of intense rainfall
rates with values widely above 1.5" into central WI and 1.75"
reaching into southwest WI. The primarily limiting meteorological
factor for heavy rainfall is the fast storm motions, so flash
flooding is contingent on the training/backbuilding risk.

Recent HRRR and RRFS runs depict scattered coverage of 1-2" totals
through this evening, but with pockets of 2-4" amounts. This is
particularly evident in the 18Z RRFS across south-central WI.
Rainfall rates per MRMS have already reached up to 2.5"/hr across
southeast MN and going forward can be expected within the heaviest
cells. Backbuilding thunderstorms appear most likely across
southern WI as the front progresses southward and lays parallel
(east-west) to the mean flow by around 00Z. Another area to
monitor will also be located where the frontal boundary proceeds
to orient in a more east-west fashion across the Green Bay, WI
area and the northern MI L.P.. Regardless, mostly dry antecedent
conditions will keep flash flooding to a mostly isolated basis,
with urban centers naturally most at risk to impacts. FFGs vary in
this region, but are lowest (below 2" per 3-hrs) across southeast
WI and into northeast IL and may be more at risk by around 00Z
tonight.

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

ATTN...WFO...APX...ARX...DVN...GRB...GRR...LOT...MKX...MQT...

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

LAT...LON   45588625 45568509 45388427 44978390 44518428
            44058522 43408564 42478585 42138734 42388974
            42829134 43269204 43709182 43919017 44458863
            45318755