AWUS01 KWNH 120851
FFGMPD
ILZ000-IAZ000-NEZ000-SDZ000-121449-

Mesoscale Precipitation Discussion 1021
NWS Weather Prediction Center College Park MD
450 AM EDT Wed Aug 12 2026

Areas affected...from eastern NE into northwest IL

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

Valid 120849Z - 121449Z

Summary...Thunderstorms should increase in coverage and intensity
across portions of IA and northwest IL into mid morning.  Hourly
rain amounts to 2.5" with local amounts to 5" are possible, which
would be most problematic in urban areas.

Discussion...A convective complex that was over northwest SD at
00z has made the turn to a more easterly path across northeast NE
and appears to have an embedded MCV as of late.  Ahead of the MCV,
showers and thunderstorms have very slowly been evolving during
the past hour or two across IA near and ahead of a frontal wave. 
Precipitable water values of 1.75-2" exist near and ahead of the
cluster.  Effective bulk shear of 40-60 kts exists here.  MU CAPE
of 3000-4500 J/kg exists across eastern NE, IA, and northwest IL.

The mesoscale guidance has been too far north with the complex. 
Conceptually, the forward propagation vectors (favoring SE
movement) and instability gradient ahead of the cluster (favoring
ENE movement) are leading to the slightly south of east movement
that has recently been observed.  Believe this movement would
continue into this morning, which would lead to a solution
somewhat south of the available mesoscale guidance.  Where
mesocyclones, cell training, or cell mergers occur, hourly rain
amounts to 2.5" and local totals to 5" would be possible.  These
amounts exceed the three hourly flash flood guidance across the
area, and this degree of rainfall would be most problematic in
urban areas.  Flash flood issues are expected to be isolated to
widely scattered.  

Roth

ATTN...WFO...DMX...DVN...FSD...ILX...OAX...

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

LAT...LON   42759806 42759446 42109049 40908933 40749182 
            41809770 

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