Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
729 PM EDT Thu Aug 27 2026
Day 3
Valid 12Z Sat Aug 29 2026 - 12Z Sun Aug 30 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST AND GREAT BASIN INTO THE ROCKIES AND FRONT RANGE,
NORTHERN PLAINS INTO THE UPPER MIDWEST, AND THE SOUTHEAST TO THE
CAROLINAS...

...Southwest and Great Basin into the Rockies and Front Range...

The upper high weakens/flattens across the Southern Plains as
troughing becomes increasingly established over portions of the
West and Northern Plains. Moisture gets funneled in between the two
features, which may have a connection to a future northeast
Pacific tropical cyclone. A Marginal Risk of excessive rainfall
remains for Sat-Sat night as above average moisture for the
monsoon fuels diurnally driven widely scattered to scattered
convection. The pattern would support isolated flash
flooding, with favored terrain, urbanized areas, box/slot canyons,
arroyos/dry washes, and burn scars being the most prone to
flooding.

..Southeast...

Showers and thunderstorms capable of producing heavy to excessive
rainfall each day should be focused in the vicinity of a quasi-
stationary front near the Gulf coast region and aforementioned
disturbance in the central Gulf, luring the dying front west as an
easterly wave Sunday and Sunday night. Increasing ridging poking
in from the western subtropical North Atlantic should lead to a
decreasing heavy rain threat across the Carolinas with time. With
precipitable water values of 2"+ expected, hourly rain amounts to
3" are possible where cells merge or train, particularly near the
Gulf Coast.

...Northern Plains into the Upper Midwest...

Pattern remains unsettled across this area during Day 3 (Sat-Sat
night), owing to shortwave energy (convectively-aided) riding along
the periphery of the upper ridge ("ring of fire"), along with the
persistent moisture anomaly in place (PWATs ~2 standard deviations
above normal). Still quite a bit of spread among the guidance QPFs;
however, given the degree of instability and moisture in play,
some of the stronger storms will be capable of intense short-term
rainfall rates and localized flash flooding.

Asherman/Hurley


...Southeast and Gulf Coast...

The tail-end of the longwave upper trough, with distinct shortwave
energy traversing the Gulf Coast as per the 00Z guidance, along
with the attendant (eventually quasi-stationary) surface front,
will provide the dynamical focus for more organized (widespread)
areas of convection across this region. While approaching and
eventually residing near the coast, the boundary will contend with
ample moisture moving northward from the Gulf, yielding multiple
rounds of storms with the potential for heavy rainfall. Flood prone
urban areas such as New Orleans, Baton Rouge, Mobile, and some of
the more interior areas of Mississippi dealing with the latest of
multiple days of heavy rains will all support widely scattered
instances of flash flooding. Rainfall and thunderstorms will bring
heavy rainfall to Alabama and Georgia as well, and the previously
mentioned trough encounters a similarly moist airmass being pushed
northeastward in the lower levels. This will support several rounds
of storms in the form of multiple lines across Georgia and parts
of South Carolina. The storms moving northeastward could allow for
some training as the cold front moves through, and could bring
widely scattered instances of flash flooding.

...Southwest...

As similarly stated in previous outlooks, a very gradual eastward
progression of the upper ridge across the Southwest should allow
for a shifting of the heaviest precipitation to the east out of
Utah and more into the central Plains. The ridge should largely
preclude much organization from the storms, so the Marginal
continues to focus on the areas where either terrain or prior
rainfall could locally increases the risk of flash flooding.

Hurley/Blanco-Alcala

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