AWUS01 KWNH 190957
FFGMPD
OHZ000-MIZ000-INZ000-WIZ000-ILZ000-IAZ000-191530-

Mesoscale Precipitation Discussion 1331
NWS Weather Prediction Center College Park MD
555 AM EDT Sat Sep 19 2026

Areas affected...Eastern IA...Southern WI...Northern
IL...Southwest Lower MI...Northern IN

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

Valid 190955Z - 191530Z

SUMMARY...Heavy showers and thunderstorms with some areas of
backbuilding and training cell-activity will continue to advance
southeastward this morning while fostering areas of flash
flooding. Some locally considerable urban flooding impacts will be
possible.

DISCUSSION...GOES-E IR satellite imagery shows strong MCS activity
with heavy showers and thunderstorms dropping gradually down to
the southeast across large areas of eastern IA, southern WI and
northern IL. This includes localized areas of backbuilding and
training convection across especially northeast IA and into
northwest IL, and this is also where some of the coldest
convective cloud tops are noted.

The convection remains aligned out ahead of a wave of low pressure
advancing east across central IA and north of a warm front that
extends east from the low center across eastern IA through central
IL and southern IN. MUCAPE values of around 1000 to 1500 J/kg are
in place across much of the region, and this coupled with the nose
of a southwest low-level jet reaching 30 to 40 kts should continue
to maintain a fairly well-organized axis of mainly elevated
convection going through the early to mid-morning hours. Enhanced
isentropic ascent and favorable jet dynamics aloft will be key
supporters of this stronger convective activity at least in the
near-term, and this will also be inclusive of some continuing
backbuilding and cell-training concerns.

PWs remain quite elevated with magnitudes of 1.75 to 2.0 inches
and this along with the instability and deeper layer moisture
transport will maintain a likelihood for some rainfall rates to
reach well into the 1 to 2 inch/hour range with even some spotty
heavier rates possible.

The latest hires model guidance suggests potential for additional
swaths of 2 to 4+ inches of rain going through the early to
mid-morning hours, with generally the heaviest rainfall totals
more likely to impact areas of eastern IA and northern IL where
there is a bit of a stronger setup for cell-training and
backbuilding convection.

Areas of flash flooding will be likely, and this will include a
corridor of impacts generally along a line from Dubuque, IA
eastward across Rockford and Chicago in northern IL, and down into
northern IN including South Bend. Adjacent areas of southwest
Lower MI may also see some potential for these impacts. Locally
considerable urban flooding will be possible across some of these
areas.

Orrison

ATTN...WFO...ARX...DMX...DVN...GRR...ILX...IND...IWX...LOT...
MKX...

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

LAT...LON 43439161 43258952 43238773 42968578 42418473
41658470 41008534 40768621 40658745 40788933
41359189 42009270 42899259

$$
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