876
AGUS74 KWCO 131511
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE MAY 13 2025

.Synopsis...
Flooding impacts possible through today for the Mid-Atlantic... River
flooding forecast across the Southeast... Elevated streams and rivers in
Intermountain West ... Isolated flooding impacts continue today for
American Samoa...

.Mid-Atlantic...
A lingering threat of flash and urban flooding remains in place today from
VA into central PA as persistent locally heavy rainfall (2 - 3" totals
WPC) continues to impact the region. Saturated antecedent conditions across
western VA and the Appalachians, with relative soil moisture generally
greater than 65% (0 - 10 cm RSM, NASA SPoRT), make the area more vulnerable
to runoff. Central VA into eastern PA has relative soil moisture closer to
50% (0 - 10 cm RSM, NASA SPoRT) suggesting there remains some infiltration
capacity. Streamflows show a similar pattern with streams running higher in
western VA and the Appalachians suggesting streams have reduced channel
capacity and thus could reach bankfull to out-of-bank flows quickly. The
National Water Model (NWM) Short Range Forecast (SRF) has been consistently
signaling the potential for rapid-onset flooding (ROF) across northcentral
VA and into southcentral PA. The time-lagged ensemble of the SRF shows the
highest ROF probabilities (25 - 75%) across steep terrain of the eastern WV
panhandle and central PA. The SRF Maximum High Flow Magnitude Forecast
continues to depict isolated stream reaches with lower Annual Exceedance
Probabilities (AEPs) suggesting that while out-of-bank flows may be
possible, they will likely also be rather isolated. These factors suggest
that flooding impacts will remain possible throughout the day but in
particular in urban areas and areas of steep terrain.

.Southeast...
Flooding impacts, including flash, small stream, and minor river flooding,
will continue for eastern portions of the Carolinas due to locally heavy
rainfall forecast today. Total rainfall of 1 - 3"+ is still expected across
the eastern portion of NC today with locally higher amounts possible
(HRRR). In the western and coastal portions of the Carolinas soils are wet
with relative soil moisture ranging between 65 - 85% (0 - 100 cm RSM, NASA
SPoRT). Steeper terrain and higher soil moisture in the Appalachians
suggest an increased chance of runoff potential should any lingering
convection persist. Minor and isolated moderate river flooding is forecast
across parts of AL, GA, and the Carolinas, and ensembles (MMEFS, HEFS) are
in fairly good agreement on there being potential for additional
minorflooding, especially in the coastal areas of NC. Signals from the
HRRR-forced National Water Model (NWM) Short Range Forecast (SRF) support
the potential for rapid rises on small streams. The 12-hr rapid-onset
flooding (ROF) probability service is showing isolated basins (HUC-10) with
25% probabilities, especially in NC. The maximum highflow magnitude
service has pockets of stream reaches in the 20% annual exceedance
probability (AEP) range in AL, GA, and the Carolinas, suggesting a higher
potential for continued but isolated flooding in those areas.

.Intermountain West...
River and stream rises continue to rise due to recent snowmelt. Snowmelt
may continue over the next couple of days but at a much lower rate than
this past weekend (SNODAS). Later today, lower elevation rainfall begins
and may keep some of the streams and rivers running high for a couple of
days. The NWM is showing some decent streamflow responses across the Upper
Snake basin across southern ID and into northeast WY. The NWM signals could
be a bit overdone however it will be good to keep an eye on the region as
this forecast rainfall materializes.

.American Samoa...
Widespread rainfall which may be locally heavy at times will bring the
potential for flooding through Tuesday.

//Smith/Leisure



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