Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Mon May 4 2026

Day 1
Valid 16Z Mon May 04 2026 - 12Z Tue May 05 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There is a non zero chance that some of the slow moving convection
near the immediate coastline may lead to isolated flash
flooding/ponding, particularly near urban areas surrounding West
Palm Beach. Easterly onshore flow into the afternoon may keep the
southeast coast with the potential for locally heavy rainfall.

Campbell

Day 2
Valid 12Z Tue May 05 2026 - 12Z Wed May 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY INTO THE OHIO VALLEY...

21Z update... The latest guidance has shifted the overall QPF
footprint to the southeast with consensus focusing the greatest
amounts from southeast Missouri to southwest Ohio. This part of the
region could have rain rates up to 1.5 inches/hour. This trend
supported adjusting the Marginal modestly to the southeast along
with a small expansion to the southwest across eastern Arkansas and
northeast into southwest New York.

Campbell

Deep layer southwesterly flow leading into the start of the period
will be drawing moisture into parts of the Plains and then
downstream toward the Great Lakes and the Ohio Valley. That large
scale picture has changed little but subtle run to run difference
in the global models and convective allowing models continues to
result in minor adjustments to the ERO. A mid- and upper-level
trough will be amplifying over the central part of North America
and a jet streak forms over the Southwest US and approaches the
Plains...the chance for showers and thunderstorms increases along
and ahead of a develops surface front. With precipitable water
values of 1.75 to 1.9 inches embedded within a broader where
precipitable water values of 1.5 to 1.75 are going to be more
common...areal average rainfall is expected to be on the order of 1
to 1.25 inches. In general this will be beneficial rain. However
there may be isolated areas where rain rates lead to local flash
flooding. There was spread between model members with the ARW core
favoring a western solution while models with an NMM core favored
areas farther east. Given the synoptic pattern and with the support
of the global models...the ERO was kept in general along and east
of the Mississippi River.

Bann

Day 3
Valid 12Z Wed May 06 2026 - 12Z Thu May 07 2026

...THE RE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE INTERIOR SOUTHEAST UNITED STATES...

21Z update... The latest guidance continued with a slight
southeastward trend with the core of highest QPF values (~2 to 4
inches) which still focus over northern portion of the
Mississippi, Alabama, Georgia and into eastern Tennessee and
western North Carolina. There was a noticeable decrease in QPF
that reaches the central/northern Appalachians which lowered the
overall risk for excessive rainfall. The Marginal Risk was reduced
back to the Tennessee/North Carolina/Virginia borders alone with a
modest narrowing on the northwest and southeast boundaries. The
Slight Risk had a minor shift to the southeast as well.

Campbell

Maintained a Slight Risk of excessive rainfall introduced by the
WPC Medium Range desk as shortwave energy drops out of Canada and
across much of the central and eastern United States. The coverage
and rainfall intensity should be increasing on Wednesday as the
best dynamics and the best Gulf moisture coverage with a frontal
boundary over the interior portion of the Southeast US.
Deterministic QPF tends to cluster in the 1.5 to 3 inch amounts
across part of the Tennessee Valley into the southern Appalachians
from Wednesday into early Thursday due to the presence of surface
dewpoints close to 70 degrees getting drawn northward from the
Gulf. Whether or not the convection evolves into line will affect
the amount of rainfall and any associated risk of flash flooding.

Bann


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt