FOUS30 KWBC 040831
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Sun May 4 2025

Day 1
Valid 12Z Sun May 04 2025 - 12Z Mon May 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE HIGH PLAINS ADJACENT TO THE SOUTHERN ROCKIES...

New Mexico...
There is a slight risk of excessive rainfall over portions of
eastern New Mexico as south to southeasterly flow draws moisture
into the region as height falls begin in response to shortwave
energy approaches. The 04/00Z suite of numerical guidance develops
heavy rainfall developing in the diurnal activity that then 
persists over the southern High Plains well into late tonight/early
Monday morning. Precipitable water anomaly values reaches 2 sigma 
over this area by 00Z Monday..with the 04/00Z HREF mean suggests 
some repeating threats for 1"/hr rates across the Slight area with 
potential for 2-3" over much of the area. The eastern portion of 
the Marginal risk area was largely left unchanged...but the western
portion of the area was trimmed to minimize overlap with heavy 
snow areas (especially over the San Juan mountains).

Great Basin...
While the probability of excessive rainfall is likely non-zero
given the showery nature of precipitation given the upper trough 
and cold mid- level temperatures aloft...the amount of rain 
shouldn't be a problem unless it all falls in under an hour.
Individual thunderstorms may result in briefly heavy
rates...but thinking is that the thunderstorms will be embedded 
within a broader field of showers circulating around the main upper
low. This should help mitigate the overall threat of flooding.

Midwest to Northeast...
The slow moving closed low embedded within a broader upper trough
continues to make its way eastward across the Ohio Valley today and
tonight. Deepest moisture of 1.25 to 1.5 inches will be eventually
be shunted off the Mid- Atlantic coast today but still stream in 
over New York back and then drawn back through northern Ohio. The 
Marginal Risk is maintained with only nudges to the
western/northern periphery of the Marginal risk area based on the
latest QPF. 

Bann


Day 2
Valid 12Z Mon May 05 2025 - 12Z Tue May 06 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS...

Texas into New Mexico...
A closed upper low over the Desert Southwest will continue to
meander eastward on Monday. Confidence remains in a focused area 
for repeating heavy rainfall south from the TX Panhandle to the NM
border where a Slight Risk remains without many changes...with main
activity occurring once again around the time of maximum daytime
heating and then persisting into or through the night. The suite 
of 04/00Z numerical guidance still shows the magnitude of 
precipitable water values to exceed 2 sigma by 00Z Tuesday with the
1.25" precipitable water line reaching the Caprock. The 12Z QPF 
consensus is for 2-4" over a sizable area just south of the TX
Panhandle...with locally higher amounts embedded in the broader QPF area.

Mojave Desert through Southern Utah...
Numerous showers with embedded daytime and evening thunderstorms is
still expected as upper low continues to meander over Arizona as 
it begins to fill. Moisture is still anomalous for this time of 
year...being some 2 to 3 standardized anomalies above climatology 
for early May...but concern would be greater for excessive rainfall
if the actual values of precipitable water values were greater and
intense rainfall rates would be sustained for a longer duration. 
As a result...the risk of excessive rainfall appears to be non-zero
but not enough to warrant a Marginal risk area based on 
coordination with local offices.

Northern Mid-Atlantic into southern New England...
Closed low will continue to meanders across portions of the Upper 
OH Valley through Monday night. Continued onshore flow brings the 
threat for repeating locally heavy rain over the northern Mid- 
Atlantic into southern New England which will have seen some heavy 
rain between now and then. A Marginal Risk is maintained.

Bann


Day 3
Valid 12Z Tue May 06 2025 - 12Z Wed May 07 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN MISSISSIPPI VALLEY/CENTRAL GULF COAST REGION...

Showers and thunderstorms capable of producing intense rainfall
rates and heavy/excessive rainfall will become more numerous  
on Tuesday as height falls make their way out across Texas and as
the parent upper low ejects out over the Southern Plains. With
increasing flow off the Gulf drawing deeper moisture on-
shore....the convection should become increasingly efficient 
rainfall makers.especially over portions of Louisiana and 
Mississippi. There is still some differences in where models place 
the heaviest rainfall...with the GFS and Canadian favoring a faster
solution while the EC/UK favoring the axis from eastern Texas into
northern Louisiana. This forecast cycle nudged the Moderate risk 
area a bit eastward but not as far east as the GFS/Canadian.

Bann

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