FOUS30 KWBC 250824

QPFERD



Excessive Rainfall Discussion

NWS Weather Prediction Center College Park MD

424 AM EDT Sat Oct 25 2025



Day 1

Valid 12Z Sat Oct 25 2025 - 12Z Sun Oct 26 2025



...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 

SOUTHEAST TEXAS INTO CENTRAL ARKANSAS AND WESTERN MISSISSIPPI...



...Previous Discussion...



Multiple rounds of heavy showers and thunderstorms are expected to

impact the broader northwest Gulf Coast region this period, with

one initial axis of on-going convection moving across parts of

eastern/southeastern Texas and advancing across western Louisiana 

and southern Arkansas. Convection presumably is interacting with a

40 kt southerly low-level jet off the western Gulf. Precipitable 

water values at or above 1.75 inches and MUCAPE values locally of 

2000 J/kg will support high rainfall rates potentially exceeding 2 

inches/hour with the stronger storms.



Additional organized convection is expected later today/tonight

with the arrival of an upper- level jet streak in the subtropical 

stream which interacts with the southern stream closed low/trough 

axis crossing the southern Plains. Even though antecedent 

conditions are quite dry, the concern for multiple rounds of 

convection which combined may yield some 3 to 5+ inch totals, will 

probably be enough to support a threat for scattered areas of flash

flooding. The more sensitive urbanized locations will be at 

greatest risk for impacts. 



...Pacific Northwest and Northwest California...



Multiple rounds of moisture transport into the coastal ranges will

continue as an atmospheric river activity continues...with greatest

rates/accumulation from later this morning into the afternoon. 

Locally a few additional inches of rain will be possible for the 

windward slopes of the terrain, but given the early-season and 

relatively modest nature of this atmospheric river activity, any 

flooding concerns are expected to be isolated at best. 



Bann



Day 2

Valid 12Z Sun Oct 26 2025 - 12Z Mon Oct 27 2025



...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF

THE MID-AND LOWER-MISSISSIPPI VALLEY, TENNESSEE VALLEY, SOUTHERN 

APPALACHIANS AND SOUTHEAST...



Maintained the Marginal risk area already hoisted for portions of

the southern United States on Sunday. Thunderstorms capable of

locally intense downpours remain possible across the immediate Gulf

coast early as southerly flow continues to tap Gulf moisture and

advect it northward...potentially as far north as the Tennessee

Valley. A front making its ways eastward should help focus

convective activity early in the period...but also help shunt it

eastward with time as surface high pressure builds in from the

west. Isolated cells have the potential to produce rainfall rates

in excess of an inch per hour prior to frontal passage. Farther

north...concern is more for quarter to half inch rain rates within

a weakly destabilized environment (200-400J/Kg MUCAPE). PWATs of 

1-2" may support any isolated instances of excessive rainfall/flash

flooding within the marginal risk area. Models are trending toward

a higher qpf solution along the Central Gulf Coast, but their

continued to be enough uncertainty in the 24/00Z guidance to

preclude any upgrades at this time.



Bann



Day 3

Valid 12Z Mon Oct 27 2025 - 12Z Tue Oct 28 2025



...|THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS A PORTION

OF THE SOUTHEAST UNITED STATES	...



Low pressure moving across the southern United States on day 2 

will begin to take a more northeastward trajectory. Given less 

favorable low level flow and a more stable atmosphere...the risk of

excessive rainfall will be diminished. Even so...the 25/00Z suite 

of numerical guidance does show spotty convection with isolated 

bulls-eye amounts of 2 inches or greater mainly in the Carolinas. 

The NAM wasfar and away the most aggressive with its amounts and 

was not given much consideration given the placement of the 

heaviest rainfall in a region where stable air was banked up 

against the east aspect of the terrain in response to the ridging 

of surface high pressure to the north. While initially easy to 

downplay the spotty nature of the model QPF...the machine learning 

first guess algorithm did point the area as a marginal risk of 

excessive roughly co-located with the WPC deterministic QPF. As a 

result...we opted to shrink the Marginal issued on Day 4 and place 

it closer to the southern portion of the Appalachians.



Bann





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