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FOUS30 KWBC 020030
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
830 PM EDT Mon Sep 1 2025

Day 1
Valid 01Z Tue Sep 02 2025 - 12Z Tue Sep 02 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
COASTAL TEXAS, CENTRAL PLAINS, AND THE EAST COAST OF FLORIDA...

...01Z Update...

...Coastal Texas...

Lingering convection from Houston southwest down the coast and into
portions of the lower Rio Grande Valley continue to pose an
isolated flash flooding threat, albeit one that is diminishing with
the loss of daytime heating. Any overnight convection will likely
be anchored offshore and therefore not pose a flash flooding
threat.

...Central Plains...

An ongoing cluster of convection over South-central Kansas is
pushing south into Oklahoma. While this convection may persist for
another few hours, it has been weakening and therefore only poses
an isolated flash flooding threat. Slower moving showers further
northeast towards northeast Kansas and Missouri may also pose a
localized flash flooding risk, though rainfall rates are far from
impressive. A few more cells may develop overnight in this region
as upper level energy is slow to exit the area.

...East Coast of Florida...

A Marginal risk of flash flooding remains for the northern half of
the east coast of Florida. A slow-moving low off the coast is
spinning a northeasterly onshore flow into much of the coast north
of Palm Beach. There remains some potential for training and heavy
rainfall with any lingering convection, though coverage should
continue to diminish overnight. The flow is offshore across south
Florida so all flooding risk south of Lake Okeechobee has ended.

Wegman

Day 2
Valid 12Z Tue Sep 02 2025 - 12Z Wed Sep 03 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHWEST AND PORTIONS OF THE UPPER MIDWEST, THE MID-SOUTH AND
TENNESSEE VALLEY, AND FLORIDA PENINSULA...


...Mid-South through Tennessee Valley...
Remnant boundaries from ongoing convection today combined with
additional lift from a digging trough from the central U.S. should
allow convective activity Tuesday to be in similar areas (and west)
from the coverage today. However, moisture is limited with the
1.25" PW today increasing to around 1.5" Tuesday (neither of which
are anomalously high). This uptick will allow for some greater
rates than today and motion should remain slow overall, but overall
the rainfall magnitude continues a decreasing trend. The Slight
Risk was downgraded to Marginal per coordination with WFOs OHX HUN
and MEG.

...Upper Midwest...
A cold front leading a developing upper low descending from Arctic
Canada will push across North Dakota by midday and Minnesota
overnight. Moisture that has streamed up the Plains over the past
couple days will greet this front with a PW of 1.25" which is 1
sigma above normal. Diurnally enhanced convection is expected fire
up along and ahead of the frontal boundary, with potential for
heavy rainfall. The Marginal Risk area remains in effect for all
but northwest Minnesota, northern Wisconsin, the western UP of
Michigan into northern Iowa.

...Florida...
The frontal boundary across the Florida Peninsula will continue to
sag south with mainly diurnally driven convection south of the
front. The farther south front means north side of the Marginal
Risk can be trimmed and the 12Z CAM consensus allows the Tampa Bay
metro to be removed.

...Southwest...
An anomalous surge in monsoonal moisture shifts up the Sierra
Nevada tonight through Tuesday due to the position of the upper
ridge axis to the east and a weak upper low along the central CA
coast to the west. PW anomalies of 2 to 3 sigma are forecast from
the lower CO River up trough the Sierra Nevada and even into
southern Oregon by 00Z Wed. Scattered diurnally driven convection
expected across this region with a maintenance of the Marginal Risk
up through the northern Sierra Nevada. Guidance is generally
struggling to produce notable QPF along the Sierra Nevada, though
the ECMWF did increase its precip there with the 12Z cycle. CAM
guidance is more keen on southern CA deserts and terrain activity
over central AZ and NM despite less moisture anomaly in NM.


Jackson


Day 3
Valid 12Z Wed Sep 03 2025 - 12Z Thu Sep 04 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PARTS OF THE
SOUTHWEST INTO THE GREAT BASIN, THE UPPER MIDWEST, MISSOURI, AND
THE SOUTHERN FLORIDA PENINSULA...

...Southwest...
Monsoonal moisture continues to stream north from the lower CO
Valley through the Sierra Nevada and much of Nevada on Wednesday,
particularly according to the ECMWF. Diurnally-driven activity can
be expected again over the Sierra Nevada which may be locally
excessive, as well as much of Nevada through western Arizona and
southwest Utah. The Marginal Risk is maintained there and trimmed
away from southeast Arizona and New Mexico where moisture trends
below normal east of the upper ridge axis.

...Central U.S...
Elevated moisture ahead of the strong cold front sweeping down the
Plains will trigger heavy rainfall again. Enough focus is present
to warrant maintenance of the Marginal Risk around the central
Great Lakes though timing is in question. The experimental RRFS
indicates some potential repeating lines over southern WI, so the
Marginal was expanded a bit to include Milwaukee. While much of the
activity should be progressive, there is a repeating threat on the
southern end of activity along the southern KS/MO border. A
Marginal Risk was introduced here.

...Florida...
Deep moisture along the stalled frontal boundary will continue to
generate convection capable of producing heavy rain across the
southern Florida Peninsula. Given the southern drift of the front
is expected to continue, the northern portions of the Marginal
Risk were trimmed out as it was for Day 2. This includes removing
the Tampa Bay metro from the Marginal.


Jackson


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