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FOUS30 KWBC 231554
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1154 AM EDT Sat Aug 23 2025

Day 1
Valid 16Z Sat Aug 23 2025 - 12Z Sun Aug 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND FOR PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES...

...Southeast into the Appalachians...

Convection that occurred on Friday has increased the amount of soil
saturation and consequently the sensitivity for flooding from
additional rainfall. With similar environmental conditions
today featuring decent CAPE, lingering mid and upper level
vorticity with a weak circulation center lingering near the
Georgia/South Carolina coastline, and elevated precipitable water
values, the threat for scattered areas of flash flooding across
the region remains for portions of Georgia and extending east to
the coast. Areal averages of 1 to 2 inches will be common with
isolated maxima upwards of 4+ inches possible near the coast.

The existing Slight Risk area was extended farther northeast along
the coast to include the greater Wilmington, NC metro area, and
the Marginal up to the Albemarle Sound given latest trends in the
CAM guidance for later today. The Slight Risk was also extended
south to include the greater Tampa Bay metro area owing to radar
trends and locally higher QPF maxima in the CAM guidance. For the
central Appalachians, the QPF has generally trended upwards
compared to previous forecasts, and therefore the existing Marginal
Risk area was extended north to include central and western WV.

...Southwestern states...

Scattered to numerous showers and thunderstorms are expected across
much of the Desert Southwest and extending eastward to include
northern NM and into much of CO. Similar to earlier forecasts, the
heaviest QPF footprint is currently situated over the Sangre de
Cristos and San Juan mountains southward into northern New Mexico
given embedded shortwave energy and orographics providing areas of
focused ascent across that region. Slot canyons, burn scar
areas, and arroyos will once again be the target of interest for
flash flood prospects with model guidance continuing to show
localized QPF maxima on the order of 1-2 inches during the time of
maximum heating that persists into the evening.

Upon further examination of the latest CAM guidance suite and HREF
flash flood guidance exceedance probs, a Slight Risk has been added
for the general vicinity of the Mogollon Rim in Arizona. Slow
moving storms forming over the terrain this afternoon and moving
over the adjacent lower elevations could raise the risk of flash
flooding more so than the surrounding areas. In addition, the
existing Marginal Risk was expanded more to the west to include the
Peninsular Range of southern California and also includes more of
the Sierra Nevada where scattered slow moving storms could also
result in some localized flooding problems.

Bann/Hamrick

Day 2
Valid 12Z Sun Aug 24 2025 - 12Z Mon Aug 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE SOUTHWEST
AND FOR PORTIONS OF THE CENTRAL ROCKIES TO THE CENTRAL PLAINS...

...West...

Maintained the Slight Risk area in parts of Utah and northern
Arizona where models still depict convection occurring over/near
vulnerable slot canyons, burn scars and normally dry washes during
from later today into the evening...much like the placement and
timing of storms that occurred on Friday. The driving forces will
continue to be weak shortwave energy embedded within the
anticyclonic flow across the Intermountain region.

Father east...the risk of excessive rainfall starts to spread out
away from the central Rockies Front Range and out over the adjacent
plains. Deep layer shear is going to be enhanced as the flow aloft
is forecast to be northwesterly at this point while low level flow
from the southeast draws air with higher dewpoints/precipitable
water values upslope. Spaghetti plots along with the RRFS continue
to show potential for 2 to 3 inch rainfall amounts extending as
far east as western Kansas by the end of the period. Given the
precipitable water values forecast...the most active convection
could drop 1 to 2 inch rainfall amounts in an hour. The previously
issued Slight was largely unchanged.

...Appalachians to Mid-Atlantic and Pennsylvania/New York...

A deepening area of low pressure north of the border will force a
cold front to sweep eastward from the Great Lakes into the eastern
third of the country on Sunday. The airmass ahead of the front
across the central and southern Appalachian chain is forecast to
have 500 to 1000 J per kg of MLCAPE and precipitable water values
generally in the 1.5 to 1.75 inch range at the start of the day
which drops during the day. The area over portions of Pennsylvania
and New York continue to have a longer window of opportunity for
locally heavy rainfall. As a result...maintained the northern end
of the Marginal risk area near a region of lower flash flood
guidance due to the potential for heavier rainfall rates and
amounts overlapping.

...Coastal North Carolina...
A weak surface feature hugging the coastline will focus and
support locally heavy rainfall near the coast of North Carolina on
Sunday and Sunday night. Present indications are that the activity
should remain off-shore. However...even a subtle slowing of its
forward speed or shift in track could bring moderate to heavy
rainfall to the immediate coastline of North Carolina late Sunday.

...Southern Georgia and northern Florida...
On-shore flow of moist air interacting with the southern end of the
front associated with the low pressure/amplifying upper trough to
the north should combine for convection capable of producing heavy
rainfall Monday and Monday evening across portions of southern
Georgia into the northern Florida peninsula.

Bann

Day 3
Valid 12Z Mon Aug 25 2025 - 12Z Tue Aug 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL ROCKIES FRONT RANGE TO THE SOUTHERN PLAINS ON MONDAY...

Broad, cyclonic flow aloft will be in place across the Plains on
Monday while low level flow should continue to be drawn northward
at low levels of the Southern Plains...with a boundary extending
front northern Texas into northeast New Mexico and southern
Colorado helping to focus late day storms. The airmass south of the
front is expected to have precipitable water values approaching 2
inches across the region and values potentially in the 2 to 2.25
inch range near the Red River. Stability does not appear impressive
at this point...but the atmosphere should support locally heavy
rainfall should convection develop anywhere between
Oklahoma/northern Texas westward into the plains of eastern
Colorado and northeast New Mexico.

The Slight Risk area was embedded within a broader Marginal Risk
area extending across much of the central and southern portion of
the Great Basin and eastward to the central and southern Rockies
Front Range. Once again...weak shortwave energy embedded within a
broad upper leads to yet another round of late day showers and
thunderstorms. Slot canyons...normally dry washes and burn scars
remain most at risk for flooding.

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