AWUS01 KWNH 171048
FFGMPD
ILZ000-IAZ000-171646-

Mesoscale Precipitation Discussion 0434
NWS Weather Prediction Center College Park MD
647 AM EDT Wed Jun 17 2026

Areas affected...in and near portions of IA & IL

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

Valid 171046Z - 171646Z

Summary...A convective complex with heavy rainfall is expected to
continue moving east-southeast over partially saturated soils and
urban areas in IA. Hourly rain amounts to 2.5" could lead to
flash flooding.

Discussion...An evolved convective complex is moving
east-southeast near 40 kts, currently aligned along its vector of
forward propagation, across portions of IA with hourly rain
amounts up to 3", nearly double the three hourly flash flood
guidance. The system is occurring within a warm advection regime
with precipitable water values ~1.5", effective bulk shear near 60
kts, and a MU CAPE pool upstream of 1000+ J/kg which is continuing
to build northward. Behind the LEWP/QLCS structure is some
attempt at backbuilding downstream (east-southeast) of a
strengthening cyclone complex in NE which is on the strong side of
June climatology, with central pressures just under 990 hPa.

The REFS guidance is too slow, and the HREF guidance a hair too
far north with this convective complex. While the complex itself
should evolve into one that is forward propagating, both mesoscale
ensemble guidance runs indicate practically no break between the
current elevated thunderstorm activity and new activity which
occurs once CIN weakens and convection becomes more surface based,
which is expected around midday. The locations unlucky enough to
be near where this transition occurs would get two quick rounds of
heavy rainfall back to back, somewhere across the northern IL.
While this occurs, a warm front should continue moving east across
the area. As flash flood guidance is low to modest after a long,
intermittent period of heavy rains, flash flooding is possible
both in the short term and whenever convection reorganizes from
elevated to surface based, which should be around the tail
end/horizon of the MPD period. Hourly rain amounts to 2.5" with
local totals to 4" could lead to flash flooding where soils are
partially saturated and over urban areas.

Roth

ATTN...WFO...DMX...DVN...FSD...ILX...LOT...

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

LAT...LON 43199399 42429238 41508885 39968924 40229060
40899226 42479551 42649453

$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/10)