646
AGUS74 KWCO 251513
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT FRI APR 25 2025

.Synopsis...
Flash and urban flooding possible across the Southern Plains, Lower
Mississippi Valley, Tennessee Valley, and portions of the Southeast...Risk
of flooding and landslides in Puerto Rico...Significant river flooding
continues along the Lower Mississippi River...

.Discussion...

.Southern Plains...
Additional showers and storms through tonight may elicit flash and urban
flooding from portions of the TX Panhandle through the Red River Valley
(northern TX/southern OK). Repeated rainfall events, particularly across
portions of north TX and southern OK, has wetted soils (60 - 80% RSM, 0 -
10 cm NASA SPoRT) and has contributed to isolated areas of river flooding
across northern TX, indicating an increased vulnerability of hydrologic
responses. In contrast, soils across the majority of the TX Panhandle are
generally on the dry side (10 - 50% RSM, 0 - 10 cm NASA SPoRT), which
should allow for ample infiltration capacity for runoff. However, there is
concern with robust rainfall rates and localized training with these
storms, which may generate runoff into low water crossings,
ditches/culverts, and other typical flood prone areas. The latest guidance
from the HRRR-forced National Water Model (NWM) increases confidence in the
hydrologic responses being highly localized, as there are only isolated
areas of potential small stream responses across the region. Additional
showers and storms on day 2 (Sat) will likely generate similar responses
across the region and spread further east into portions of the Ozarks
(eastern OK/western AR).

After a brief reprieve in rainfall on days 3 - 4 (Sun - Mon), additional
rainfall returns to the region on days 5 - 6. However, given the current
convective pattern and differences in model guidance, the exact location
and magnitude of hydrologic responses remain uncertain.

.Lower Mississippi Valley, Tennessee Valley, and portions of the
Southeast...
Diurnal showers and storms (some heavy at times) across these regions may
generate flash and urban flooding through tonight. The wet pattern that has
taken shape over the region has contributed to wet to saturated top soils
(60 - 80% RSM, 0 - 10 cm NASA SPoRT) and elevated streamflows to above
normal historical flows (USGS), indicating diminished infiltration capacity
and vulnerability to hydrologic responses. While impacts are not expected
to be widespread, localized training convection may quickly overwhelm
current capacity, leading to rapid runoff into nearby urban drainages and
small streams. The HRRR-forced NWM has been consistent with indicating the
potential for scattered small stream response across much of MS, northwest
AL, and southern middle TN through the afternoon hours, with basin average
probabilities of rapid-onset flooding between 25 - 50%. Corresponding AEPs,
per the High Flow Magnitude Forecast, suggest mostly within channel stream
rises (AEPs at or greater than 50%). However, more localized significant
impacts may occur in areas where storms train and where more robust
rainfall rates materialize.

.Puerto Rico...
Periods of heavy rainfall associated with diurnal storms may generate urban
and small stream flooding across Puerto Rico through early next week, with
the most significant impacts expected days 3 - 5 (Sun - Tue). Landslides
are also possible, particularly in areas of steep terrain and more
saturated soils following periods of rainfall over the past week.

.Lower Mississippi River...
Significant river flooding along the mainstem of the lower Mississippi
River (AR/MS/LA) will continue for the foreseeable future as the flood wave
continues downstream. The floodwave is near Arkansas City, AR and
Greenville, MS, as crests in moderate flood stage are expected in these
locations this weekend. Significant rises are still expected from Vicksburg
to New Orleans over the next week, with the river in Baton Rouge expected
to crest in major flood stage mid to late next week. Showers and storms are
expected across the region over the next several days, which may briefly
delay ongoing recessions and crests however, renewed rises are not
expected.

//JDP





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