Mesoscale Precipitation Discussion 0926
NWS Weather Prediction Center College Park MD
824 PM EDT Fri Oct 05 2018

Areas affected...ERN IA...NRN IL...SRN WI...FAR NRN MO

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

Valid 060023Z - 060523Z

Summary...Impacts from flooding and flash flooding will become
more likely late this evening and overnight.

Discussion...At 00Z thunderstorm activity was expanding in
coverage and intensity over eastern Iowa and northern Illinois.
While seasonably strong steering flow will carry individual
thunderstorms east quickly, the large scale environment supports
back-building and training from west to east, acting to boost
event totals. Additionally, storms were occurring where Most
Unstable CAPE values were near 1000 J/kg and precipitable water
values upwards of 1.50 inches or more were 2.0 to 2.5 standard
deviations above climatology - and supportive of somewhat heavy
hourly rain rates.

Going forward in time the hi-res models depict rain rates
exceeding one inch per hour in the MPD area, and this would meet
the one inch per hour Flash Flood Guidance values over this rather
saturated portion of the Upper Midwest. The convection was
breaking out slightly earlier than anticipated overall, and hence
the 22Z HRRR offered one of the better solutions. The 18Z NAM
CONUS Nest was also close to the correct placement. Merging QPF
output from those two models with the RAP CAPE and low level
convergence fields, we would expect the heaviest storms to train
from far southern Iowa / northern Missouri over to near Chicago,
with moderate rain rates extending farther north into Wisconsin.
Noting that dual-pol rain rates from KDVN were already beginning
to nose above 1"/hour, we would expect some 2.00-plus inch amounts
in isolated locations through 05Z. Some flash flooding appears
likely.

Burke

ATTN...WFO...DMX...DVN...EAX...ILX...LOT...MKX...

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

LAT...LON   42698838 42308752 41278812 40349395 41219419
            42349079