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FOUS30 KWBC 311556
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Sun Aug 31 2025

Day 1
Valid 16Z Sun Aug 31 2025 - 12Z Mon Sep 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHERN NEW
MEXICO THROUGH EASTERN TEXAS...

...16Z Update...

...Central Plains...

Abundant cloud cover across the central Plains as well as ongoing
shower activity have greatly reduced the available instability for
what very little convection is ongoing. This light activity is
expected to continue through the day and into tonight. Despite the
long duration, it`s unlikely that except in very isolated
instances, that there will be much embedded heavy rainfall across
the area. Further, the rain that is expected is likely to fall in
areas that have been very dry in recent days, displaced from where
the heavier rains have occurred further west. Thus, it appears that
the flooding threat has waned down well into the Marginal category.
Thus, the Slight Risk is downgraded with this update.

...New Mexico into Texas...

A stalled out front will continue to provide the forcing for widely
scattered shower and thunderstorm activity across much of central
Texas. Lingering monsoonal moisture across New Mexico and a stalled
out trough in place along the Mexican border should also result in
scattered shower and thunderstorm activity across the region. Wet
soils, particularly across southeastern New Mexico will support
flash flooding with any slow moving storms that produce heavy
rainfall. HREF probabilities for FFG exceedance generally range
between 10 and 40 percent across the Slight Risk area of New Mexico
and Texas, so the Slight remains largely unchanged. What did change
was that the Slight was trimmed southward out of the Dallas-Fort
Worth Metroplex with this update. Much of the instability and
forcing is south of the Metroplex. While there may be some recovery
of the instability with afternoon heating, allowing for some
afternoon convection, the cells capable of heavy rain should be
isolated enough for a Marginal Risk.

For eastern Texas, the complex of thunderstorms pushing south down
I-45 is expected to weaken with time as additional convection and
increased competition for the available instability results in a
decrease in organization. However, expect additional convection to
develop out ahead of the line, likely in and around the Houston
metro. Abundant moisture and instability in place along the Texas
Gulf Coast will support stronger convection capable of multiple-
inch-per-hour rainfall rates. PWATs across southeast Texas are well
over 2 inches, so there is more than enough moisture in place for
any convection to have the opportunity to produce heavy rainfall.

For central and Western Texas, while moisture decreases with
increasing longitude, the moisture that is in place is still up to
2 sigma above climatological norms all the way into far eastern
Texas. Thus, while convective coverage will be lesser in west Texas
than further east, the storms will still be capable of producing
widely scattered instances of flash flooding, particularly when
they move over more flood prone clay soils near the Big Bend
region.

Wegman

Day 2
Valid 12Z Mon Sep 01 2025 - 12Z Tue Sep 02 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR THE
SOUTHERN TIER, PLAINS AND TENNESSEE VALLEY...

A frontal system and a shortwave or two aloft will support storms
with higher rain rates across the Lower Missouri/Mid-Mississippi
Valley and the Tennessee Valley to Southern Appalachians. The
Marginal Risk areas for the Tennessee Valley and for the Plains
remain in effect for this period.

The stalled frontal boundary along the Gulf Coast and into Texas is
expected to advance a little southward during this period leading
to the QPF footprint being offset from prior days which will limit
the flooding potential. The heaviest rain is still expected to
focus along the I-10 corridor from Houston to San Antonio and may
still cause impacts. A broad Marginal Risk remains in effect from
the Southwest, southern Texas/western Gulf coastline an much of the
Florida peninsula.

Campbell


Day 3
Valid 12Z Tue Sep 02 2025 - 12Z Wed Sep 03 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST/CALIFORNIA, FLORIDA, LOWER MISSISSIPPI/TENNESSEE
VALLEYS AND THE UPPER MIDWEST...

A Marginal Risk area was maintained for the Mid-South as shortwave
energy and a weak low traversing the cold front may trigger
convection capable of higher rainfall rates over the region.
Meandering frontal boundaries within an unstable environment will
support heavy rainfall and localized flash flooding potential for
Florida, therefore the Marginal Risk area was kept for this period.

A cold front will drop into the Northern Plains and Upper Midwest
ahead of the strong reinforcing upper trough. Convection is
expected fire up along and ahead of the frontal boundary, with
potential for heavy rainfall. A Marginal Risk area is in effect for
the eastern Dakotas, northern Iowa, Minnesota, northern Wisconsin,
and portions of the UP of Michigan.

Meanwhile, monsoonal moisture is forecast to flow into the
southwestern U.S. underneath the mean upper ridge for scattered
showers and thunderstorms. A Marginal Risk span from southern
Colorado/New Mexico westward to eastern California.

Campbell


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