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FOUS30 KWBC 010753
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
353 AM EDT Mon Sep 1 2025

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

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN TIER, PLAINS, EAST COAST OF FLORIDA, AND TENNESSEE
VALLEY...

The stalled frontal system and monsoonal moisture will persist
across southern Arizona, New Mexico, and Texas. Isolated convection
across the region expected, keeping the threat for flash to
isolated instances. A Marginal Risk remains in effect for portions
of Arizona, New Mexico, and western/southern Texas.

Easterly onshore flow into Florida warrants maintaining a Marginal
Risk for the eastern coastal areas.

Antecedent dry conditions along the Appalachians should preclude
any flash flooding. Better coverage of convection should stay
further west into central Tennessee and northern Alabama. A vort
max tracking east across Tennessee will be the forcing mechanism
for any convection across Middle Tennessee. A Marginal Risk was the
appropriate threat level for this period.

Finally, the Marginal in the Plains was reshaped to a slightly more
SW-NE orientation rather than mostly N-S. Instability and abundant
cloud cover should limit the flooding threat, but prior rains from
previous days in the form of more saturated soils could support an
isolated flash flooding risk.

Campbell/Wegman


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

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDDLE TENNESSEE VALLEY...

Remnant convection from the overnight period on Monday night will
persist into Tuesday as a reinforcing shortwave digs southward and
reaches Middle Tennessee by Tuesday night. A weak, but still
significant low level jet will advect Gulf moisture northeastward
across the Deep South and into Tennessee on Tuesday, which will
keep a steady supply of fuel in place for any convection. Thus,
expect a long-duration rain event, that while much of it will be
light, the LLJ advecting moisture into Tennessee and various
different sources of forcing will support some storms becoming
strong and able to produce heavy rain. The storms will also be
slow-moving, which will lengthen the amount of time any area sees
heavy rain. A Slight remains in effect for portions of Mississippi,
Alabama, and Tennessee.

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.

The stalled out front across Florida will support more widespread
convection Tuesday afternoon across much of the Peninsula, while
the Panhandle dries out a bit from prior days` rains. A second
shortwave and associated front will produce areas of heavy rain
across portions of the upper Midwest. A Marginal Risk remains in
effect for most of central and southern portions of the Peninsula.

Monsoonal moisture is forecast to flow into the southwestern U.S.
underneath the mean upper ridge notably shifted a bit westward for
this period. Scattered convection expected across the region and
is covered by a Marginal Risk spanning from eastern California,
Arizona, New Mexico and into southern Colorado.

Campbell/Wegman


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, FLORIDA, AND THE UPPER GREAT LAKES/UPPER MIDWEST...

Deep moisture along the stalled frontal boundary will continue to
generate convection capable of producing heavy rain across the
Florida Peninsula. A Marginal Risk is in effect for most of
central and southern portions of the state. Meanwhile, monsoonal
moisture and diurnal heating will continue to trigger convection
across the West/Southwest maintaining an elevated threat for
isolated flash flooding for vulnerable locations. A Marginal Risk
is in effect from New Mexico to eastern California. Further north,
heavy rainfall is expected across portions of the Upper
Midwest/Upper Great Lakes as the frontal boundary continues to
advance eastward. A Marginal Risk encompasses portions of Wisconsin
and northern Michigan.


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