508
AGUS74 KWCO 301515
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SAT AUG 30 2025

.Synopsis...
Flash and urban flooding possible through Sunday across the Central
Plains...Isolated flooding possible across New Mexico and West Texas and
the Texas Hill Country into the Southeast this weekend...Lingering small
stream and river flooding in Alaska...

.Central Plains...
Showers and thunderstorms, with locally heavy rainfall (4+" of rainfall
possible), may elicit isolated flash and urban flooding through day 2 (Sun)
across portions of NE and KS. Antecedent conditions are not generally
conducive for flooding as soils are very dry and streamflows are below
annual median flows for the area of concern. However, given the potential
for robust rainfall rates with these storms, these conditions may be
locally overwhelmed, leading to rapid rises on small streams and pluvial
ponding in low-lying and poorly-drained areas. The HRRR-forced National
Water Model (NWM) is indicating isolated to scattered small stream
responses across the region, with peak flows expected later tonight.
Corresponding annual exceedance probabilities (AEPs), per the High Flow
Magnitude Forecast, indicate some potential for rapid stream rises (20%
AEP) particularly across southern NE. However, some higher magnitude flows
(AEPs 10% or less) are noted across the region, indicating an isolated
potential for significant small stream rises. Training convention will be
the primary driver for flooding impacts.

.Texas Hill Country into the Southeast...
A stalled frontal boundary will provide a focus for locally heavy rainfall
across portions of the TX Hill Country and east TX through day 2 (Sun) and
across portions of the Lower MS Valley and Southeast through early next
week, eliciting isolated flash and urban flooding. With exception to
far-eastern TX, where soils are more primed from recent rainfall,
antecedent conditions across the Hill Country and the remainder of eastern
TX are not favorable for flooding given dry soils and streamflows near or
below annual means for this time of year, precluding a larger and more
widespread flood threat. Regardless, given the potential for robust hourly
rainfall rates with these storms, antecedent conditions may be locally
overwhelmed, especially in urban areas and in the complex terrain of the
Hill Country. There is little to no response from the NWM, likely due to
dry soils and the model using higher annual recurrence interval thresholds
(3.2 ARI compared to the standard 1.6 ARI), across the region. Impacts are
most likely in areas of low-water crossings and typical flood-proned areas
in urban centers. Similar impacts are expected further east across the
Lower MS Valley and the Southeast over the next few days, although this
activity is not expected to be as widespread as in recent days.
Nevertheless, soils are primed from rainfall over the past few days and
locally heavy rainfall may generate flooding of small creeks/streams and
flooding in typical flood-proned areas.

.New Mexico and West Texas...
Daily afternoon thunderstorms, with locally heavy rainfall, may elicit
isolated instances of flash and urban flooding across the region through
day 2 (Sun), especially in and around recently burned areas. Convective
activity over the past several days have primed soils, particularly across
eastern NM and the TX Panhandle, suggesting some hydrologic sensitivity to
additional rainfall. Flooding of low-water crossings, arroyos, and rapid
rises in areas of steep/complex terrain are possible. Flash flooding and
debris flows are also possible near recently burned areas. Both the GFS and
NBM-forced NWM are indicating the potential for isolated small stream
responses across this region over the next 24 hours. Corresponding AEPs are
generally at or greater than 50%, which suggests that most stream rises
should remain within the channel. However, there are isolated AEPs at or
below 20%, supporting the potential for rapid stream rises and flooding
impacts outside of recently burned areas.

.Alaska...
Small stream and minor to moderate river flooding will continue across
portions of western AK and south-central AK due to runoff from recent
rainfall. Rivers across these regions are currently at or near crest and
will remain in flood through early next week.

//JDP





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