829
AGUS74 KWCO 241518
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SAT MAY 24 2025

.Synopsis...
Considerable flooding is likely this holiday weekend across portions of the
Plains into the Southeast...Flash, urban, and small stream flooding, along
with landslides is possible through today in American Samoa...

.Central and Southern Plains into the Southeast...
Several rounds of moderate to locally heavy rainfall will continue through
day 2 (Sun) across much of the region, which will likely cause considerable
flash and riverine flooding. Rainfall totals of 1 - 3", locally higher, is
forecast over the next 48 hours across much of the area with the highest
forecast rainfall across the portions of the Ozarks and surrounding basins.
MMEFS indicates many of these basins have already received 1 - 3" with Bull
Shoals Lake (MO) and James (MO/AR) river basins experiencing nearly 6" of
rainfall over the past 24 hours. Soils are wet and streamflows are
increasing due overnight rainfall that has primed the hydrologic systems.
River ensemble guidance continues to suggest minor to isolated moderate and
major flooding is also possible beginning early next week as the high water
flows are routed out of the headwaters and streams and into the mainstems.

By late day 2 (Sun) into day 3 (Mon) the system sags to the south which may
elicit some additional flooding responses from central TX through the
portions of the Southeast. These regions have experienced a rather wet
spring season, and as such remains susceptible to enhanced runoff, due
reduced infiltration rates, into streams and rivers that are generally
running above their climatological normals. This would suggest that while
widespread flooding is unlikely, training rainfall over vulnerable basins,
due to the aforementioned wet season, may elicit rapid rises on streams and
creeks, new and renewed river flooding, and an increased pluvial flooding
risk. The system then lingers through mid-week next week with small pockets
of heavy rainfall possible which could keep conditions primed, and slow
recessions of mainstem rivers.

The HRRR-forced National Water Model (NWM) is signalling rapid-onset
flooding and high water on small streams and rivers. Rapid-onset flooding
probabilities of 26 - 50% concentrated around southern MO, much of AR,
eastern OK, and western TN with peak flow arrival times occurring late
tonight. The NBM-forced NWM is also suggesting some of the larger order
rivers may peak through day 4 (Tue) due to regulated flows and routing of
water from the tributaries. High Water Magnitudes probabilities remain
similar as previous discussions at generally 50 - 20% annual exceedance
probabilities the most significant responses continue to shift around
slightly in the Ozarks as low as 4% AEPs. With the compounding factors of
vulnerable hydrologic systems and heavy rainfall rates, particularly during
the overnight hours, this event will likely generate significant flooding
impacts through the holiday weekend.

.American Samoa...
Widespread showers, with embedded heavier rainfall rates, may cause flash,
urban, and small stream flooding, along with landslides in areas of steeper
terrain through today (local). Flooding of roadways, low-lying areas, and
out-of-bank responses from streams are the likely responses from this event.

//JAC

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