AWUS01 KWNH 311306
FFGMPD
INZ000-ILZ000-MOZ000-IAZ000-311800-

Mesoscale Precipitation Discussion 0765
NWS Weather Prediction Center College Park MD
905 AM EDT Wed Jul 31 2024

Areas affected...southeast Iowa, northeast Missouri, central
Illinois

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

Valid 311305Z - 311800Z

Summary...Convection continuing in the vicinity of an MCV moving
into Illinois will train to the east through the morning. Rainfall
rates of 1-3"/hr are likely, which could result in 2-3" of rain
with locally higher amounts. Flash flooding is possible.

Discussion...A localized spin noted in the regional radar mosaic
over west-central Illinois is associated with a
convectively-enhanced MCV which has spun out of an overnight MCS
tracking across Iowa. Although the general organization of this
MCS has weakened a bit with the veering of the LLJ, a southward
advancing outflow boundary (OFB) west of the MCV is continuing to
be a focus for additional convection. The thunderstorms blossoming
along this axis are responding to convergent moist flow as 15-20
kts of 850mb wind converges into the OFB. This is producing
enhanced ascent through convergence and isentropic lift, into an
environment favorable for heavy rain rates due to PWs of nearly 2
inches and MLCAPE of 1000-1500 J/kg. Radar estimated rain rates
from KDVN have been around 1.5"/hr in the training convection,
leading to FLASH responses of 250 cfs/smi unit streamflow beneath
ongoing flash flood warnings.

The high-res CAMs are in general agreement that this MCS will
persist for a few more hours before decaying, but there is quite a
bit of variability in placement and intensity which is reflected
by low qpf EAS probabilities. The HRRR and ARWs are a bit
suppressed with the axis of heavier rainfall, in general, which is
reasonable and supported by the ingredients and placement of the
OFB which should be the primary focus for additional redevelopment
this morning. Regardless, rainfall rates of 1-2"/hr are likely,
with the HRRR 15-min rainfall accumulation forecasting up to 0.75"
in some areas, suggesting short-duration 3"/hr rates are possible.
With thermodynamics continuously being drawn into the OFB and mean
850-300mb winds aligned to that boundary, training of echoes is
supported as storms regenerate and advect to the E/SE, following
the instability gradient around the periphery of a ridge to the
west. Where the most prolonged training of the most intense rates
occurs, 2-3" of rain is possible with locally higher amounts.

Far southeast Iowa through much of Illinois has been wet in the
past 7 days, with rainfall as much as 300% of normal leading to
0-40cm soil moisture from NASA SPoRT that is above the 95th
percentile. This suggests that any heavy rain will quickly
overwhelm soils leading to rapid runoff, and where training takes
place could result in instances of flash flooding.

Weiss

ATTN...WFO...DMX...DVN...EAX...ILX...IND...LOT...LSX...

ATTN...RFC...MBRFC...NCRFC...OHRFC...NWC...

LAT...LON 41469188 41319027 41108931 40698826 40028769
39308760 38838805 38668869 38798963 39349110
39919240 40309323 40869332 41149310 41409266

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