FOUS30 KWBC 080809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Wed Oct 8 2025

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

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

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 MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST AND EASTERN FLORIDA...

...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
ARIZONA, SOUTHERN UTAH, AND SOUTHWESTERN COLORADO...

...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
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