987
AGUS74 KWCO 111512
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE MAR 11 2025

.Synopsis...
Moderate rainfall and forecast river flooding in Florida Panhandle and
South Georgia...Snowmelt resulting in rises on rivers and streams in
Eastern Oregon into Idaho...Additional rainfall beginning tomorrow in
California...Flooding impacts possible late this week through the weekend
in the Lower Mississippi Valley into the Ohio Valley...Snowmelt and
rainfall flooding possible early next week in the Northeast...

.Discussion...

.Florida Panhandle and South Georgia...
Rivers and streams near the Georgia and Florida line will remain elevated
through the rest of the week into the weekend. The St Marys river near
Macclenny is expected to remain in flood stage through Thursday. No
additional significant rainfall is expected over the next week allowing
streams and rivers to recede unimpeded.

.Eastern Oregon into Idaho...
Snowmelt in the higher elevations near Malheur River at Vale (VALO3) and
moderate rainfall over the region is expected to result in increased stream
flows including the potential of minor to isolated moderate flooding on
area rivers. Current forecasts indicate streams start to rise on and crest
by day 2 (Wed). Additional rises may be possible this weekend.

.California...
Multiple rounds of rainfall are forecast to impact the region on days 2 - 6
(Wed - Sun), with the heaviest rainfall expected on day 2 into day 3 and
again on day 6. Top soils are wet (55 - 70%, 0 - 10cm RSM, NASA SPoRT) in
areas along the coast, north of Santa Maria to Eureka, as well as the
Sierra Nevada, suggesting some infiltration capacity remains to mitigate
impacts. However, with streamflows being above normal, once infiltration
capacity is met, significant increases on streams will be possible.
Additionally, HEFS indicates the potential of only action stage rises at
the 10% exceedance probability, further building confidence that widespread
impact will be mitigated. The only exception will be in areas in or around
recent burned areas, where the likelihood of flash flooding will increase.

.Lower Mississippi Valley into the Ohio Valley...
Heavy rainfall will bring the potential for flooding impacts starting day 4
(Fri) and through the weekend. Recent rainfall has wetted soils (60 - 80%,
0 - 10 cm RSM, NASA SPoRT) and streamflows are normal to much above normal
indicating a diminished infiltration capacity across much of the Southeast
with relatively drier conditions northeast into the Ohio Valley. Little to
no precipitation is expected though Thursday, allowing soil moisture and
small streams to decrease, increasing both soil and stream capacity and
mitigating widespread impacts. However, given the potential for multiple
rounds of rainfall, flash, small stream and river flooding will be
possible. The deterministic National Water Model (NWM) Medium Range
Forecast (MRF) indicates the potential for Rapid Onset Flooding over much
of the Lower Mississippi into the Ohio Valley. However, AEPs across much of
the region are at or above the highwater threshold (50%). The NWM does
indicate the potential for more significant stream rises from Tennessee
into Kentucky with AEPs of 2 - 20%. Given this is still 5 days out, these
signals are likely to move between now and the event as they have over the
past few days.

.Northeast...
Potential for widespread, potentially significant, flooding impacts is
increasing across the region for late this weekend into early next week.
High elevation snow will begin to melt today, slowly increasing stream
flows and soil moisture through the week. Late in the week and into the
weekend, moisture will surge into the region resulting in rapid snow melt.
With up to 8" of SWE available to melt out, along with 1 - 2" of rainfall
forecast early next week, the potential for flooding on small streams and
rivers continues to increase. Ensemble guidance across the region suggests
at least minor river flooding in this region with GEFS and NAEFS indicating
the potential of isolated major river flooding, increasing confidence in
flooding impacts.

//GKendrick



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