FOUS30 KWBC 240831
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Wed Sep 24 2025

Day 1
Valid 12Z Wed Sep 24 2025 - 12Z Thu Sep 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE
TENNESSEE AND OHIO VALLEY REGIONS...

...Southern Plains to the Central and Southern Appalachians...

Overall, no large-scale changes to the previous outlook areas,
maintaining a broad Marginal Risk that extends from portions of
central and southern Texas to the southern and central 
Appalachians, with an embedded Slight Risk centered over parts of 
the Ohio and Tennessee valleys. 

Composite radar this morning shows widespread showers and storms 
extending from the Ohio Valley back into the southern Plains. The 
overnight CAMs indicate that ongoing storms along the far eastern
Oklahoma-Texas border into southern Arkansas will remain organized
into the late morning as the drift slowly south, with training 
storms likely to produce heavy amounts across portions of 
northeastern Texas and northwestern Louisiana. Supported by 
shortwave energy moving through the base of a broader-scale 
positively-tilted upper trough and PWs at or above 2 inches, HREF
probabilities indicate locally heavy amounts exceeding 3 inches are
likely. However, dry soil conditions, reflected by high FFGs, are 
expected to limit the threat for widespread flooding concerns.

As energy continues to move through the base of the upper trough,
an area of low pressure is expected to become better organized and
track northeast through the Ohio Valley beginning later this
afternoon and continuing into the overnight. Deep southwesterly
flow ahead of the wave will support increasing moisture, with PW
anomalies increasing to over 2 std dev above normal per the GFS.
Given the ongoing rains and relatively wetter soil conditions
(lower FFGs), a Slight Risk extending from far northern Alabama to
far southern Ohio and western West Virginia was maintained. HREF 
probabilities indicate that amounts of 1-2 inches will be common, 
with locally heavier amounts over 3 inches possible within the 
Slight Risk area.

In the wake of the low, showers and storms producing heavier rates
are expected along the trailing front as it sinks south through 
the lower Mississippi Valley and along the upper Texas coast back 
into South Texas. Here too, the HREF is indicating locally heavy 
amounts over 3 inches are likely. But similar to areas to the 
north, higher FFGs suggest flooding issues will be mostly contained
to vulnerable areas, including urbanized centers.

...Northeast...

The general consensus of the CAMs shows an area of showers and
storms moving northeast well in advance of the system over the Ohio
Valley. Supported by deepening moisture along a slow-moving
boundary and increasing mid-to-upper level forcing, showers and
storms will advance northeast across Pennsylvania, with repeating
storms potentially resulting in locally heavy amounts from
northeastern Pennsylvania into the lower Hudson Valley/NYC area. A
A Marginal Risk was maintained for areas where the HREF shows 
higher probabilities for amounts over 2 inches and where FFGs are 
relatively lower.

...Southeastern Lower Michigan...

An upper low closing off this morning is expected to remain
centered over Lower Michigan into Thursday morning. Showers and
storms are likely to develop east of the center, with relatively
deeper moisture wrapping into the system raising the potential for
locally heavy rainfall rates. A small Marginal Risk was 
introduced, highlighting the area where the HREF shows high 
probabilities for accumulations exceeding 2 inches.

...Central California...

A slow-moving upper low currently offshore will drift north and
begin moving inland Thursday morning. With anomalous moisture
remaining in place (2.5-3 std dev above normal), locally heavy
amounts will remain possible. Reflecting the high HREF
probabilities for amounts over an inch, a Marginal Risk was
maintained along the central California Coast from the Monterey 
Bay south and along the adjacent mountains. 

Pereira


Day 2
Valid 12Z Thu Sep 25 2025 - 12Z Fri Sep 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
ARIZONA AND FAR SOUTHWEST NEW MEXICO...

...Southwest to Sierra Nevada...

After moving inland early Thursday, the closed low over central
California is forecast to drop south into southern California by
early Friday. With ample moisture remaining in place (2-3 std
dev above normal) near and east of the upper center, locally heavy
amounts are possible from the Sierra Nevada east into southern 
Nevada and southwestern Utah.

As the center drops south, increasing southerly flow east of the
low will draw deeper moisture up from Mexico, fueling widespread
shower and thunderstorm coverage, especially across southeastern
and central Arizona into southwestern New Mexico. A Slight Risk 
was maintained across this area where PWs are forecast to increase 
to 1-2 standard deviations above normal by the afternoon.

...Northeast...

Unsettled weather developing Day 1 is forecast to continue into 
Thursday as showers and storms continue to develop ahead of the 
system lifting out of the Ohio Valley into the Northeast. 
Strengthening southwesterly flow along the Mid Atlantic coast into 
the Northeast will support deepening moisture (PWs increasing to ~2
inches) and an increasing threat for heavy rainfall rates. A 
Marginal Risk was maintained from northern New Jersey into southern
New England, where HREF probabilities indicate that localized 
amounts over 3 inches are possible late Thursday morning into the 
afternoon.

...Southern Appalachians...

The consensus of the latest guidance indicates that showers and
storms developing along and ahead of the cold front trailing the 
low moving through the Northeast will be generally progressive. 
With widespread heavy amounts not expected and FFGs high, the 
previous Marginal Risk was removed from much of the Mid Atlantic. 
However, some models do show the potential for training storms to 
produce some localized heavy amounts (2+ inches) across parts of 
the southern Appalachians, where a small Marginal Risk was 
maintained.

Pereira


Day 3
Valid 12Z Fri Sep 26 2025 - 12Z Sat Sep 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
ARIZONA AND SOUTHWEST NEW MEXICO...

...Southwest...

A second day of numerous showers and storms is expected across the
Southwest, especially for much of southeastern Arizona and parts of
southwestern New Mexico. The upper low setting into southern
California the previous period is expected to move little this day,
remaining centered near the California/Mexico border. This will
help to maintain anomalous moisture across the region, fueling
widespread shower and thunderstorm coverage during the afternoon 
and evening hours. A Slight Risk, with a footprint similar to the 
Day 2 area, was maintained for Day 3 across parts of Arizona and 
New Mexico.

...Southeast...

A boundary will remain in place across the Southeast as an upper
trough evolves into a closed low that is forecast to linger beyond
the period. Moisture and energy lifting ahead of the closing system
will support periods of shower and storms. While the guidance at
this point is not signaling any widespread heavy amounts, the
pattern does lend itself to at least the threat for locally heavy
amounts, which may raise at least isolated flooding concerns.

Pereira
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