FOUS30 KWBC 070829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Tue Oct 7 2025

Day 1
Valid 12Z Tue Oct 07 2025 - 12Z Wed Oct 08 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
KENTUCKY, MIDDLE TENNESSEE, THE UPPER OHIO VALLEY, AND NEW MEXICO...

...Mid-South through the Upper Ohio Valley and Central Appalachians...

A weak mid-level vorticity maxima (currently over far northeastern
Arkansas) will trek east-northeastward across Kentucky through 
most of the day. This feature will likely maintain at least some of
its organization given persistent convection near and east of its 
center and sufficient downstream instability. Areas of 1-3 inch 
rainfall totals are expected with this feature, and an uptick in 
convective coverage should occur later today as surface heating 
promotes destabilization within a moist airmass downstream of the 
feature. Slow cell movement and localized training/backbuilding are
both expected to prompt areas of excessive runoff through the 
forecast period especially within the Slight Risk area.

Later today, height falls from a larger scale trough centered over
Hudson Bay will aid in additional convection along a front that
will sweep through the region. Storms may redevelop across Kentucky
and Tennessee, although the degree of coverage will be heavily 
modulated by the degree of lingering instability behind the initial
wave of daytime convection expected across those areas. A pool of 
at least 1.5 inch PW values should remain - supporting heavy 
rainfall with any lingering convection through the evening hours.

Additional convection is expected along the aforementioned cold
front across New York State and western New England. Storm motions
should be relatively fast (30+ knots), limiting any heavy rainfall
to any localized areas of training that can materialize.
Additionally, antecedent dryness/drought should limit excessive
runoff potential. A Marginal risk extends to western Pennsylvania
and vicinity - although this risk seems a bit too isolated farther
northward to include or expand in any probabilities at this time.

...New Mexico...

A southwestward moving cold front will stall close to the higher
terrain across central New Mexico today through tonight. Upslope
flow behind this front and weak mid/upper waves traversing the
state will both initiate deep convection within a sufficiently
moist airmass (0.7-1.25 inch PW) for heavy rainfall. Storm motions
across northern portions of the state may be quick enough to limit
rainfall, yielding a mostly isolated flash flood threat in areas 
that are sensitive (i.e., burn scars, low-lying areas). Central and
southern portions of the state should experience slower storm 
motions and perhaps multiple rounds of convection from afternoon 
through the overnight hours. Given increase in convective coverage 
and potential for local 3+ inch rainfall totals occurring 
perilously close to sensitive areas/burn scars, a Slight Risk was 
introduced with the expectation of at least a few instances of 
excessive runoff given the scenario.

...Southeastern Florida...

Local 1-2 inch rainfall totals are expected across urban areas of
Southeastern Florida from Miami northward through West Palm Beach
and Port Saint Lucie. The greatest risk of these downpours
materializing will occur from midday onward due to peak
heating/destabilization. Additionally, onshore flow/coastal
flooding may hinder runoff processes beneath any heavier downpours,
locally enhancing flash flood risk. One or two instances of flash
flooding cannot be ruled out, and a Marginal Risk is in place to
address the threat.

Cook


Day 2
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...

Some continuation of heavy rainfall potential will exist across New
Mexico during the early morning hours of the D2/Wed forecast
period. During the day, an increase in insolation/destabiliztaion
should promote development of isolated to scattered thunderstorms
initially along terrain/ridgelines near the Arizona/New Mexico
border and across the southern Rockies. Storms will drift
slowly/erratically while producing brief heavy rainfall. Typical
low spots/sensitive areas will experience a flash flood threat with
this activity. Coverage of flash flood potential should be sparse
enough to warrant continuation of a Marginal Risk and associated
probabilities.

Cook


Day 3
Valid 12Z Thu Oct 09 2025 - 12Z Fri Oct 10 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS A LARGE
PART OF THE SOUTHWEST AND SOUTHEASTERN FLORIDA...

...Southwest...

Models are consistent in depicting a dramatic increas in
atmospheric moisture content across the Colorado River Valley from
both Hurricane Priscilla and the Gulf of California. Widespread
1-1.75 inch PW values are expected by midday Thursday. This 
moisture will combine with deep southwesterly steering flow and 
weak mid-level waves aloft to produce several areas of 
precipitation throughout the forecast period (including the 
overnight and early morning hours). A close inspection of point 
forecast soundings from model data casts some doubt on the extent 
of instability developing within the moist axis due to widespread 
cloud cover. Any daytime destabilization within the region will 
likely lead to stronger convection and an increased risk of flash 
flooding. Trends in instability will be monitored for possible 
upgrades in parts of the Marginal Risk area in later outlooks.

...Southeastern Florida...

Models depict a few areas of convection developing very close to
urbanized areas of southeastern Florida during peak heating hours.
Point forecast soundings across the area depict typically 
moist/unstable profiles (2+ inch PW values), though wind fields are
very weak, suggesting slow/erratic cell movement and mergers. Spots
of 1-3 inch/hr rain rates could materialize, supporting an urban
flash flood risk across the area.

Cook
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