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FOUS30 KWBC 050808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Sep 5 2025

Day 1
Valid 12Z Fri Sep 05 2025 - 12Z Sat Sep 06 2025

...THERE`S A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHWEST, PORTIONS OF THE TENNESSEE VALLEY, AND FOR SOUTH FLORIDA...

...Southwest...

Monsoonal moisture combined with some of the remnant moisture from
Lorena will impact much of the Southwest today. However, with
Lorena`s low-level circulation now expected to dissipate offshore
and not move northeastward into northern Mexico, the share of that
moisture making it into the Southwest has been steadily decreasing.
The result is less coverage of showers and storms in favor of a
more showery weather regime. In coordination with TWC/Tucson, AZ
and EPZ/El Paso, TX forecast offices, the inherited Slight Risk for
portions of Arizona and New Mexico was removed with this update.


...Tennessee Valley...

Training thunderstorms, some of them severe, on the tail end of a
wound-up occluded front, will track northeastward along the western
side of the Appalachians this afternoon and evening. While the
storms are likely to be fast-moving, the influx of moisture
parallel to the cold front approaching from the northwest will
favor a period this afternoon where storms could redevelop and
train along the same areas in the form of multiple clusters of
storms. Thus, a new Marginal Risk was introduced covering Middle
Tennessee and into eastern Kentucky. The greatest threat of flash
flooding looks to be in the urban areas in and around Nashville.

...South Florida...

A stalled out tropical wave at the tail end of a front well off the
Eastern Seaboard will continue to plague much of the Florida
Peninsula with showers and slow-moving and erratic thunderstorms
this afternoon into this evening. While the bulk of the expected
rainfall is expected to target south Florida and the Keys, some of
that rainfall activity may sneak a bit further north into central
Florida. The greatest threat for flash flooding will be into the
highly urbanized I-95 corridor from Palm Beach through Miami this
afternoon and this evening. Given inherent uncertainty with where
the storms will set up and how they will be moving, a Marginal Risk
remains in place, though local areas where storms are the most
persistent could quite possibly have higher-level impacts.

Wegman

Day 2
Valid 12Z Sat Sep 06 2025 - 12Z Sun Sep 07 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERMOUNTAIN WEST, FLORIDA, AND THE NORTHEAST...

...Intermountain West...

Monsoonal moisture will continue to steam northward across portions
of the West on Saturday. While some of that moisture can be
directly attributed to the remnants of Lorena, Lorena will have
long since ceased existing as a tropical entity by this period on
Saturday. Thus, the forcing mechanisms for heavy rain will turn to
more typical monsoonal factors, such as upsloping and an impinging
shortwave trough. For some areas, this will result in a higher
threat for heavy rain and subsequent flooding, particularly into
far southern Arizona and much of New Mexico. Nevertheless, no one
forcing will be strong enough to promote organization and more
robust heavy rains, so the Marginal Risk for the area remains in
place. Further north, a digging shortwave trough will be the
primary focus driving the heavy rain, as the storms tap into some
of that monsoonal moisture.

...Northeast...

The cold front that was moving into the Appalachians on Friday will
continue across the urban corridor of the Northeast on Saturday.
Diurnal heating and robust moisture transport up the I-95 corridor
will support training storms, which may be locally enhanced with
upslope flow from the DC Metro area northeast through Boston and
into Maine. Corfidi Vectors parallel to the frontal interface
suggest fast-moving training thunderstorms will be common. The
widespread urbanization along I-95 also supports at least a
Marginal/isolated flash flooding risk. It will be far from a rainy
day for most, with most areas staying dry. However, when storms
move through, they will likely be strong, with abundant moisture to
tap into. Thus, the inherited Marginal Risk was expanded well south
and west to include all of the I-95 corridor through the DC Metro
area. Localized urban flooding will remain the primary threat from
any repeating storms despite very dry antecedent conditions. The
front will continue eastward into Saturday night, ushering in yet
another cool and very comfortable air mass from Sunday through much
of next week. The rainfall forecast has most notably increased
across portions of New England, from NYC north. This is where the
greatest risk of flash flooding will be on Saturday.

...Florida...

The stalled out front and associated tropical wave will slowly
begin to retrograde back towards the north on Saturday, resulting
in a spreading of the potential for heavy rains well up the Florida
Peninsula. Thus, the Marginal Risk was expanded north through
central Florida with this update. High uncertainty as to
convective coverage and behavior will keep a Marginal going for the
time being, but there remains some potential a later Slight may be
needed in portions of Florida.

Wegman

Day 3
Valid 12Z Sun Sep 07 2025 - 12Z Mon Sep 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND THE FLORIDA PENINSULA...

...Southern Plains...

While some monsoonal moisture will linger in portions of the West
into Sunday, there will be far more of a Gulf component to the
moisture as predominant southeasterly flow advects deep Gulf
moisture into south Texas, which will combine with what moisture is
left from the monsoon. While the moisture will be plentiful, the
forcing will be anything but, as a strong upper level ridge builds
across the area. The result will be storms that for many areas will
be tied to the mountains, cold pools from other storms, or
localized pockets of higher instability. Thus, storm organization
across Texas on Sunday will be quite lacking. Given this, despite
the atmospheric moisture, soils across south Texas are quite dry,
which is average for this time of year. Thus, for most areas, rain
from any storms will be largely beneficial and will soak into the
ground, precluding much flooding threat. Thus, in coordination with
EWX/San Antonio, TX, CRP/Corpus Christi, TX, and SJT/San Angelo, TX
forecast offices, the inherited Slight for portions of the Hill
Country was removed with this update.

...Florida Peninsula...

It`s the same old song and dance weather-wise across Florida once
again on Sunday. The front that has been stuck there will still be
there, taking advantage of plentiful Gulf/Atlantic moisture.
Uncertainty with how the storms will form and organize remains
high, so the Marginal Risk remains in place, with a northward
expansion included to account for potentially heavy rains across
central Florida from the day Saturday continuing into Sunday.

Wegman


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