519
AGUS74 KWCO 111517
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SUN MAY 11 2025

.Synopsis...
Isolated flooding impacts through early this week expected for The
Southeast and The Mid-Atlantic... Snowmelt runoff for the Intermountain
West into this week... Isolated flooding impacts through today for Puerto
Rico and the USVI... Ongoing river flooding across eastern Texas/Louisiana
and the Northeast...

.The Southeast...
Heavy rainfall continues to bring the potential for flooding impacts from
MS through SC today before shifting northward into NC/VA on days 2 - 3 (Mon
- Tues).

Rainfall is already ongoing this morning across parts of FL, AL, GA, and
SC, and the potential for flooding impacts will increase as it continues
through the day today. With precipitation totals of 1 - 3"+ expected across
the region today (WPC) on top of the 1 - 3"+ that fell yesterday (24-hr
MRMS), flash, urban, and small stream, and minor river flooding are all
possible. Topsoils are generally close to saturation across the region (60
- 90% RSM, 0 - 10 cm, NASA SPoRT) but despite the recent rainfall, pockets
of FL, GA, and SC remain on the drier side, which will help mitigate
flooding impacts from the today`s rainfall. Streamflows are elevated across
MS and AL, but gradually become closer to normal/below normal further to
the northeast in GA and SC. Minor river flooding is forecast across parts
of MS, AL, and SC, and ensembles (MMEFS, HEFS, SR PQPF) are in fairly good
agreement on there being potential for additional minor or isolated
moderate flooding, especially in coastal GA/SC. Signals from the
HRRR-forced National Water Model (NWM) support the potential for rapid
rises on small streams, with the 12-hr rapid-onset flooding (ROF)
probability service showing isolated basins (HUC-10) with 25%
probabilities, and these signals are only expected to increase throughout
the day. The highflow magnitude service has pockets of stream reaches
exceeding in the 20 - 4% annual exceedance probability (AEP) range in AL/GA
and the FL Panhandle, suggesting a higher potential for impactful flooding
in those areas.

.The Mid-Atlantic...
The system moves into NC and VA on days 2 - 3 (Mon - Tue) and is expected
to bring rainfall totals of 2 - 5" across the region. The flooding threat
will mostly be flash, urban, and small stream in nature, but isolated minor
river flooding is also possible. Antecedent conditions are on the drier
side, with topsoils in the 30 - 50% RSM range and streamflows running at
near to much below annual mean flows. These conditions will initially help
to mitigate flooding impacts, but areas that see high totals and embedded
high rainfall rates could see significant flooding. The highest threat for
flash flooding will be along the upslope of the Blue Ridge Mountains where
rainfall totals are higher (4 - 5"+) and complex terrain will enhance
runoff. Minor flooding is already forecast in the Rocky and South Fork
Catawba basins, and river ensembles (MMEFS, HEFS) indicate a 30% chance or
greater for at least isolated minor river flooding in NC/southern VA. The
NBM-forced NWM is showing mostly highwater exceedance (1.3 year ARI) and
scattered reaches exceeding the 50% AEP threshold, but overall signals
continue to be muted and may be underdone, especially along the
aforementioned upslope of the Blue Ridge.

.Intermountian West...
Snowmelt (SNODAS) and associated runoff will continue into early this week
as above normal temperatures spread across the region. This will elevate
streamflows and lead to isolated small stream flooding impacts (flooding of
rural mountain roads, low-water crossings, etc). Regions of particular
concern include the Sangre de Cristo, Tusas, and Jemez mountains in
northern NM, the San Juan and Sangre de Cristo Mountains of south-central
Colorado, and the Absaroka Range/Bighorn Mountains (MT/WY). Across these
regions, soils are moist and streamflows are elevated heading into this
weekend, so runoff should be able to produce efficient small stream
responses. Any precipitation is expected to be very minimal and not
exacerbate the snowmelt runoff.

.Puerto Rico and the USVI...
Water surges, isolated landslides, urban, and small stream flooding are all
possible through this weekend as periods of heavy rainfall continue across
the saturated islands.

.Ongoing River Flooding...
Minor to isolated moderate and major river flooding is ongoing in East
TX/LA and the Northeast. Most locations have crested, but some of the
slower responding rivers will remain in flood status through the week.

//Bliss



$$