983
AGUS74 KWCO 081523
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
10:15 AM CDT THU MAY, 8 2025

.Synopsis...
Flooding possible across the Gulf Coast into the Southeast... Localized
urban and small stream flooding is possible in the Mid-Atlantic and
Northeast... Flash flooding is possible today in response to rainfall and
snowmelt across Northern New Mexico... Flash and small stream flooding,
along with landslides, are possible this week in American Samoa...Lingering
rainfall may cause isolated flooding impacts in Puerto Rico and the USVI...
River ice breakup increasing in Alaska... Ongoing river flooding will
continue Southern Oklahoma through east Texas and northern Louisiana...

.Gulf Coast into the Southeast...
All flooding hazards are possible through day 7 (Wed), with variability in
exact timing, for portions of eastern LA, MS, AL, FL, GA, SC, and NC in
response to multiple days of scattered showers and storms. Cumulative
precipitation totals of 2 - 5", locally higher, are expected across the
region. LA, MS, and portions of western AL are already wet with relative
soil moistures of 60 - 90% (0 - 100 cm RSM, NASA SPoRT). GA, FL, and SC,
are somewhat drier with most deep layer relative soil moistures ranging
between 10 - 50% (0 - 100 cm RSM, NASA SPoRT). Many rivers across the
entire region are elevated with normal to above normal streamflows due to
ongoing and previous rainfall with the exception of FL which has below
normal streamflows (USGS). There is still some inherent uncertainty with
the extent and magnitude of potential flooding given this event will span
numerous days, but at minimum scattered flash flooding and areas of minor
river flooding can be expected through day 7 (Wed). Isolated moderate river
flooding cannot be completely ruled out.

The NBM and GFS forced National Water Model (NWM) Medium Range Forecasts
(MRF) are showing rises across the region with some variability as to
timing and magnitude. Rises in TX, LA, and MS will continue today, with
some mainstem rivers not cresting until at least day 3 (Sat) or beyond.
River rises in GA and SC will begin late this weekend into early next week
with low potential for rapid onset flooding and flows with annual
exceedance probabilities below 20% for northern FL through southern SC are
possible, however this region has the driest antecedent conditions which
should mitigate much of the initial hydrologic response. Ensemble guidance
shows potential for minor to isolated moderate river flooding as well
(MMEFS, HEFS, SR PQPF ensembles). Overall, flooding potential is variable
for the region, but there looks to be at least a minimal threat for
isolated flash and river flooding for the regions entirety.

.Mid-Atlantic and Northeast...
Localized urban and small stream/river flooding is possible today through
day 3 (Sat) due to persistent and locally heavy rainfall across portions of
the Northern Appalachians and New England. High water probabilities range
between 51 - 75% for much of the area (NWM MRF), particularly across
eastern NY and western New England. Recent rainfall and snowmelt has primed
the region leaving relative soil moistures ranging between 75 - 95% (0 -
100 cm RSM, NASA SPoRT). Rivers for the entire region are elevated with
much above normal streamflows due to ongoing and previous rainfall (USGS).
While widespread significant flooding is unlikely, the Susquehanna River is
expected to reach minor flood status, and ensemble guidance (MMEFS, HEFS)
shows potential for isolated river flooding by the end of this week.

.Northern New Mexico...
Flash flooding is possible today in response to rainfall and snowmelt of
0.5 - 1" (SNODAS). In particular, recently burned areas, creeks, streams,
low lying, and flood-prone areas are under threat from excessive runoff.
Cumulative QPF through today may total in the 0.5 - 0.75" range across the
area. Previous days have seen active precipitation leaving most relative
soil moistures ranging between 60 - 90% (0 - 100 cm RSM, NASA SPoRT). With
little infiltration capacity due to past rainfall and steep terrain being
at and in the foothills of the Sangre De Cristo Mountains, there is enough
evidence to suggest flooding could occur.

.American Samoa...
Flash, urban, and small stream flooding may continue today and through the
weekend due to prolonged rainfall across the island. The most significant
flooding impacts are likely to occur in low-lying areas and areas that may
be poorly drained. Previous weeks have also seen some active weather
causing saturated soil conditions. Most of the island is mountainous topped
with thin erodible soils, making them now favorable for landslides at the
base of steep slopes. Current forecast trends suggest a break in the
rainfall today with wet conditions returning day 2 - 3 (Fri - Sat)
favorable for elevated flooding risk.

.Puerto Rico and the USVI...
Localized flooding, including flash flooding, will be possible across much
of the island today through day 3 (Sat). In particular, the interior and
western sections are vulnerable due to continued rainfall and
thunderstorms. While the most significant impacts may have peaked,
antecedent soil conditions and stream flows are still vulnerable to
additional rainfall. This may result in mudslides/landslides, quick river
rises, and water surges.

.Alaska...
River breakup is underway in portions of AK, with minor to moderate
flooding possible on portions of the Yukon River as well as sections of the
Lower Kuskokwim river. In addition, several rivers north of the Alaska
Range and south of the Brooks Range have been characterized by steady stage
rises with intermittent rapid spikes indicative of ice jamming and
releasing. Flood potential on these rivers is expected to continue through
this week as breakup fronts continue to push downstream.

.Southern Oklahoma into Louisiana...
Ongoing river flooding will continue through tomorrow day 2 (Fri) due to
previous rainfall across portions of the region.

//DPL

$$