Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
817 PM EDT Sun May 17 2026
Day 1
Valid 01Z Mon May 18 2026 - 12Z Mon May 18 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
PLAINS TO THE UPPER MIDWEST...

01Z Update: General model consensus with the expected convective
evolution across the Central Plains and Midwest led to a relative
continuity in the inherited MRGL risk across the region. Some
adjustments were made to reflect where convection has since ended,
or trends away from impact overnight allowed for a removal with the
biggest change over much of Wisconsin. Environmental conditions are
ripe for heavy rainfall within a well-defined warm sector
positioned over the Missouri and Mississippi River Basins to the
south of a quasi-stationary front draped over the Plains into the
Midwest. Northern inflection of the front is situated over eastern
SD through northern IA and the WI/IL border. Greatest threat for
heavy rainfall is likely in the buoyant environment just
downstream of a twin pair of lows analyzed over KS and SD,
respectively. HREF neighborhood probabilities maintain moderate
values (30-50%) for areas of 2" or greater overnight across the
Missouri River basin from southeast NE down through northwest MO,
including the KC metro. Upscale growth of thunderstorms
materializing over KS and NE will migrate east with the mean flow
trajectory signaling a relative east to east-northeast storm motion
during the height of the convective impact. Any singular cell
generation will likely merge overnight due to cold pool mergers and
a maturing LLJ enhancement.

Classic quick-moving cells will hopefully limit training
prospects, however we will be monitoring the area along I-70 in
eastern KS into MO as perhaps the one place where outflow
prominence could spur up a period of enhanced low-level convergence
that in tandem with the LLJ placement could offer a window for
redevelopment over the same areas for a few hours at some point
between 00-06z before everything finally kicks eastward or
dwindles. The MRGL risk was sufficient at this time as the
signature was modest, at best, so decided to maintain general
continuity from the previous forecast.

MRGL risk over FL from previous update was dropped as cells will
decay in intensity with the loss of diurnal heating after 01z
leading to a degraded chance for flash flooding for the urban
southwest coast of FL. A few cells could still drop a decent amount
of rainfall prior, but FFG's remain very high over the region, so
everything will be very isolated in general. Didn't think it was
necessary to keep the risk with such a short time period of
interest.

Kleebauer


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt