077
AWUS01 KWNH 200800
FFGMPD
ILZ000-MOZ000-IAZ000-NEZ000-201300-

Mesoscale Precipitation Discussion 0766
NWS Weather Prediction Center College Park MD
359 AM EDT Sun Jul 20 2025

Areas affected...much of IA and adjacent portions of far northeast
NE, northwest IL, and northeast MO

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

Valid 200755Z - 201300Z

Summary...Hourly 1-2" rainfall to result in additional localized
2-5" totals through early morning. Isolated to scattered instances
of flash flooding are likely.

Discussion...Disorganized clusters of convection from earlier in
the evening have gradually organized into a more defined heavy
band of precipitation overnight, leveraging persistent low-level
moisture transport and convergence favorably offset by the
right-entrance region of a ~110 kts over the Lower Great Lakes.
The mesoscale environment is otherwise characterized by MLCAPE of
1000-2500 J/kg, PWs of 1.7-2.2" (between the 90th percentile and
all time record max value, per OAX sounding climatology), and
effective bulk shear of 30-40 kts. While the WNW-ESE oriented band
of heavy rainfall should make gradual eastward progress within the
deep layer mean flow (~25 kts towards the east), locally hourly
rainfall is estimated to be as high as 2" with very efficient
rates supporting 15-min totals up to 1" (per MRMS estimates).

Observational trends suggest the flash flood threat has yet to
peak this morning, and isolated to scattered instances of flash
flooding are likely to develop as the coverage of 2"+ localized
totals increases (as 2" it generally the upper-end threshold for
3-hr FFG across the region). While the FFG exceedance probs from
the HREF are not overly impressive (peaking near 30%), the suite
of guidance has a low bias overall based on the observational
trends. The experimental RRFS/REFS guidance was preferred with the
hourly RRFS runs in particular having the best, most consistent
handle on the character of the convection (while depicting
additional localized totals of 2-5").

Churchill

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

ATTN...WFO...DMX...DVN...EAX...FSD...ILX...LOT...LSX...OAX...

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

LAT...LON   42789586 42729394 42509196 42079010 41288893
            40118950 39869242 40769391 41109452 41329533
            41569651 42119711