FOUS30 KWBC 280829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Sun Sep 28 2025

Day 1
Valid 01Z Sun Sep 28 2025 - 12Z Sun Sep 28 2025

...THERE'S A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF NEW
MEXICO AND PORTIONS OF FAR WESTERN TEXAS/SOUTHERN COLORADO...

...Four Corners/Southwest...
An upper trough centered over the Southwest will continue 
directing mid-level vortices northward through the Four Corners 
region today. Moisture from Tropical Cyclone Narda in the East 
Pacific will continue surging north into the Four Corners, where 
scattered showers and thunderstorms are likely to proliferate throughout
the day. PWATs between 1-1.5 inches within the right entrance 
region of the upper jet and modest instability around 500-1000+ 
J/Kg (MLCAPE) could yield rain rates between 0.5-1 in./hr., 
especially where the slight risk is currently drawn. Burn scars, 
scars slot canyons and upslope areas within the risk areas are 
especially vulnerable to flash flooding. 

HREF's neighborhood exceedance probabilities of 2 in. in 24 hours 
are between 25-50% while EAS probabilities of exceeding 0.5 in. 
hover around 20-40% within the depicted slight risk area.


...Southeast...
An upper trough will pivot eastward over the Southeast while 
moisture from T.C. Nine continues surging northward toward the 
Southeast Coast. Current guidance keeps the axis of heaviest QPF 
offshore, but enough moisture may propagate far enough north and 
west to interact with a surface front draped along the coast and 
produce localized excessive rainfall. HREF EAS exceedance 
probabilities of 1 inch in 24 hours are between 5-15% along much 
of the Carolina Coast today, which supports the marginal risk area
depicted.

Kebede

Day 2
Valid 12Z Sun Sep 28 2025 - 12Z Mon Sep 29 2025

...THERE'S A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CAROLINA COAST...

...Southeast...
Guidance continue to depict T.C. Nine propagating north toward the
Southeast Coast on Monday, while a surface front draped along the 
coast acts as the focus for heavy rainfall. QPF has trended 
downward given slowing trends in the track of T.C. Nine on Monday.
The GFS suite in particular diverges most from the Canadian and 
Euro suites when depicting the system's slower forward motion. 
Despite this, enough moisture should work its way into the coast
and interact with the surface front to generate scattered thunderstorms.
There'll be enough moisture (1.5-2.5in PWATs) and instability 
(1000+ J/KG MUCAPE) present to support rainfall rates in excess of
1 in./hr..

...Northern California/Great Basin/Southern Cascades...
An upper low centered over the East Pacific will send mid-level 
vortices into the West Coast on Monday. Pacific moisture may 
collide with the remnant tropical moisture from Narda to produce 
heavy rainfall from northern California into the Great Basin. 
Synoptic forcing provided by a strong surface cold front should 
focus PWATs in the range of 0.75-1.25 in. to produce quarter inch 
rain rates along the immediate coast. More robust instability over 
the Great Basin should yield higher rain rates between 0.5-1 
in./hr. in some areas. Upslope enhancement may generate higher 
totals in parts of the terrain.

Kebede

Day 3
Valid 12Z Mon Sep 29 2025 - 12Z Tue Sep 30 2025

...THERE'S A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CAROLINA COAST...

...Southeast...
The inherited marginal and slight risk areas along the Southeast 
Coast were downsized based on trends in the guidance suggesting 
T.C. Nine's hard turn out to sea on Tuesday. Despite the resulting
smaller QPF footprint than previous cycles, the flash flood risk 
remains. Instability will be negligible (less than 500 J/Kg 
MUCAPE), which supports the possibility that the flood threat will be
due to runoff over saturated soils from Sunday and Monday's 
rainfall. Exceedance probabilities of over 2 inches is over 10% in
the 00z ECENS/CMCE, while below 10% in the GEFS along the 
immediate Carolina Coast.

Kebede
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