013
FOUS30 KWBC 081944
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Wed Oct 8 2025

Day 1
Valid 16Z Wed Oct 08 2025 - 12Z Thu Oct 09 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NEW MEXICO, EASTERN ARIZONA AND SOUTHERN COLORADO...

...16z Update...

The marginal risk was expanded north into southern Colorado based,
in part, on HREF probabilities of 24 hour qpf exceeding 0.5-1"
around 5%. PWATs between 0.5-0.75 should interact with shortwave
energy and rotating around the western periphery of a large Central
U.S. ridge. 200-400 MUCAPE could provide enough instability to
support hourly rates high enough to produce isolated instances of
flash flooding over sensitive areas.

Kebede

...Previous Discussion...

Ongoing shower and thunderstorm activity will exist on an isolated
basis across central and south-central New Mexico near higher
terrain. Slow movement, localized backbuilding, and proximity to
burn scars will be the likely modulators of flash flood potential
through the early morning hours.

Later in the afternoon, thunderstorm activity is expected to
develop across western New Mexico and eastern Arizona in an
environment characterized by 0.7-1.0 inch PW values, mid-level
instability, and weak wind fields beneath 500mb. Slow moving cells
with brief heavy rainfall are likely, though coverage should remain
isolated. The greatest flash flood threat should exist where
heavier rain can materialize in/near typical low spots/burn scars.
Most of this activity should be diurnally driven, with weakening
expected in tandem with low-level stabilization after the 03-06Z
timeframe.

Cook

Day 2
Valid 12Z Thu Oct 09 2025 - 12Z Fri Oct 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE DESERT SOUTHWEST, NORTHWESTERN ARIZONA AND SOUTHWESTERN
UTAH...

...2030z Update...

A slight risk was introduced in coordination with local offices
based on an increasing signal for excessive rainfall in the
guidance. The dynamic setup remains mostly the same as mentioned in
the previous discussion. Moisture from Priscilla will stream north
into the Southwest and Four Corners beginning tonight. PWATs from
1-1.5" will represent a maximum amount present across all forecast
hours for much of the Southwest beginning Thursday afternoon. These
PWATs will be 5-6 standard deviations above average. 12z HREF EAS
probabilities of exceeding 1" in 24 hours are between 15-20% over
portions of southwestern Utah, where several vulnerable slot
canyons exist. There are probabilities between 50-70% near
Flagstaff/Mogollon Rim, where upslope enhancement may occur.

Minor adjustments were made to the marginal risk area over eastern
Florida.

Kebede

...Previous Discussion...

...Southwest...
Moisture content across much of the Southwestern U.S. will increase
dramatically in tandem with strengthening southerly mid-level flow
downstream of a mid-level trough along the California coast and
trajectories emanating from Hurricane Priscilla. Modest surface
heating will allow for areas of convection to drift northeastward
across the Marginal Risk area throughout the day - perhaps
beginning as early as 12Z Thursday. Models depict the greatest risk
of deeper convection occurring from northwestern Arizona into
southwestern Utah during the afternoon/evening, and some of this
development could extend into southern Nevada as well. Additional
thunderstorm activity may occur across the eastern Transverse and
Peninsular Ranges in southern California on an isolated basis. The
primary mitigating factor for a more widespread flash flood risk
is limited insolation/surface warming due to cloud cover. One or
two focused corridors for heavier precipitation may develop within
the broader Marginal contingent on stronger destabilization due to
afternoon sunshine. Should this scenario materialize, a small area
of higher probabilities/ and categorical Slight Risk may be
needed.

...Florida...
Models (particularly CAMs) depict deep moist convection across the
east coast of Florida during the afternoon and evening hours. As
typical for the region, abundantly moist thermodynamic profiles
will combine with weak kinematics for slow-moving cells with local
2-3 inch/hr rates at times on an isolated basis. These cells will
pose an urban flash flood threat from Daytona Beach southward to
Miami/Dade metro. Weak onshore flow has also contributed to a
coastal flood risk that might hinder runoff potential and
exacerbate flood concerns on a localized basis.

Cook

Day 3
Valid 12Z Fri Oct 10 2025 - 12Z Sat Oct 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS
NORTHERN/CENTRAL ARIZONA, SOUTHERN/EASTERN UTAH, AND SOUTHWESTERN
COLORADO...

...2030z Update...

The slight risk was expanded farther south into the Mogollon Rim in
coordination with FGZ, based on growing confidence in a widespread
heavy rainfall threat. 12z Ensemble exceedance probabilities of
over 1" are generally between 20-40% with the Euro mean surpassing
40% in many parts of western Colorado and eastern Utah. Maximum
PWAT anomalies are expected to continue surging into the Southwest
and Four Corners region through Friday.

Little to no changes were made to the marginal risk along the
Southeast Coast. Most of the precipitation is expected to stay
offshore on Friday.

Kebede

...Previous Discussion...

...Southwest...
A second consecutive day of abundant moist advection will be
underway during the D3 forecast period as Priscilla drifts
northward and a slow-moving mid-level trough persists along the
California coastline. Models are generally higher with instability
parameters (500-1000 J/kg MUCAPE) compared to prior days across
the Marginal and Slight Risk areas while maintaining abundantly
moist profiles (PW values ranging from 1-2 inches). Areas of
heavier rain are expected, with deeper convection possible in the
Slight Risk area from northern Arizona into southwestern Colorado.
Some of these heavier downpours will occur atop sensitive
terrain/slot canyons and burn scars - posing a locally significant
flash flood risk. While specific timing of convection remains a
challenge at this timeframe, it is possible that multiple rounds of
convection develop and migrate northeastward across the region
throughout the forecast period. Widespread 1 inch rainfall totals
are expected, with local amounts potentially exceeding 3 inches in
a few spots.

...Southeastern U.S. Coastline...
Models are in agreement that a low pressure will develop and
strengthen substantially over the Gulf Stream just east of Florida
during the forecast period. Low-level easterlies will strengthen
dramatically and eventually become northeasterly during the
forecast period. These low-level wind fields will contribute to a
coastal flood risk while also hindering runoff processes near areas
that experience heavy rainfall. The heavy rainfall threat is a bit
conditional especially with northward extent across the Carolinas
coastlines. Nevertheless, model guidance generally depicts a few
areas of heavy rainfall especially across eastern Florida during
the first half of the Day 3 forecast period (Friday morning).
Trends will need to be monitored for any westward trend in
development of this low closer to land areas, which may increase
the heavy rainfall threat substantially. At this time, isolated
flash flood/runoff issues are expected, warranting continuation of
a Marginal Risk along coastal areas.

Cook


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