Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Thu Jun 11 2026
Day 1
Valid 12Z Thu Jun 11 2026 - 12Z Fri Jun 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST...

.Midwest to southern Plains...
Early this morning, a frontal wave developed over the central
Plains ahead of a strong upper level trough that will lift into the
Midwest today. This wave of low pressure is forecast to surge
northeast into the Midwest and be accompanied by an area of
enhanced convection in the vicinity of the low. A strengthening low
level jet on the leading edge of this disturbance will bring a
surge of moisture (PWAT values > 2 inches) and instability (MUCAPE
> 3000 J/kg) into the Midwest and create a sheared environment that
will allow for organized convection with highly efficient rainfall
rates up to 2-4 inches per hour. A Slight Risk of excessive
rainfall is in effect for portions of the Midwest where the hi-res
CAMs are showing the highest rainfall totals. There was some
consideration of upgrading to a Moderate Risk for portions of Iowa,
Wisconsin, and Illinois given recent heavy rains and soil
saturation, but the highest rainfall totals today are forecast to
be displaced to the north of where the heaviest rain fell on
Wednesday, which should keep the risk of flash flooding more in
line with a high-end Slight. On the backside of the frontal wave,
the cold front will surge southeast across the central and southern
Plains this afternoon with showers and storms expected to form
along the front. Given the highly moist and unstable environment on
the warm side of the boundary, these storms will be capable of
producing high rainfall rates, but the progressive nature of the
front should help limit the risk of flash flooding. A Marginal Risk
area extends back into the southern Plains where locally heavy
rainfall may lead to isolated instances of flash flooding.

.Ohio Valley to Mid-Atlantic...
An upper level shortwave trough is expected to move southeast
across the Ohio Valley and Mid-Atlantic today, which will provide
upper level support for the development of scattered showers and
storms this afternoon. Warm, moist air will be in place across
these regions, with PWAT values generally ranging from 1.75-2
inches, which will support rainfall rates of 1-2 inches. Elevated
instability (>2000 J/kg) should allow for some deeper convective
cells that will be capable of producing locally heavy rainfall.
Isolated instances of flash flooding will be possible, especially
if heavy rain occurs in urban environments, so there is a Marginal
Risk of excessive rainfall extending from the Ohio Valley to the
Mid-Atlantic. Northwesterly upslope flow will also result in
enhanced precipitation totals along the central Appalachians that
could create isolated flooding concerns in this region as well,
which is included in the Marginal Risk area.

.Southwest Florida...
Southeasterly flow has increased PWAT values above 2 inches across
Central and South Florida, which will allow for very heavy
rainfall rates of 2-4 inches per hour in convection along the sea
breeze boundaries this afternoon. Hi-res CAMs show the Atlantic and
Gulf sea breezes colliding over Southwest Florida, which could
result in flash flooding concerns for urban areas. Therefore, there
is a Marginal Risk of excessive rainfall for urban areas along the
west coast of the Florida Peninsula from Tampa south.

Dolan


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