003
AGUS74 KWCO 271524
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
10:15 AM CDT WED AUG 27, 2025

.Synopsis...
Potential for flooding across the Central and Southern Plains, Lower
Mississippi Valley, and Gulf Coast States... Isolated flash and urban
flooding expected across the West... River rises/potential flooding in
Alaska...

.Central and Southern Plains, Lower Mississippi Valley, and Gulf Coast
States...
A slow-moving precipitation system, including embedded heavy rain, will
track southeastward across the Central and Southern Plains through day 1
(Wed), reaching the Lower Mississippi Valley and Gulf Coast states (MS/AL)
by days 2 - 3 (Thu - Fri). The primary risk is localized runoff-driven
flash flooding, with the nature of the threat evolving as the system
progresses. The highest precipitation, up to 5" in a 24-hour period, is
forecast through day 2 (Thu), posing a potential flash flood risk to urban
areas, poorly draining regions, and steeper terrain. Antecedent conditions
are generally unfavorable across the region, as relative soil moisture is
generally below 40% (0 - 10 cm, NASA SPoRT) and streamflows are generally
near or below annual means for this time of year (USGS). However, it is
possible that these conditions will be  least locally overwhelmed given the
potential for more robust hourly rainfall rates (up to 2"/hr). While
widespread river flooding isnt expected, isolated minor river flooding is
forecast across southeastern KS, and isolated areas of significant river
flooding are possible if heavier rainfall rates overcome current dry
conditions. Both the GFS and NBM-forced National Water Model continue to
indicate isolated small stream responses in southeastern Kansas (near
Wichita) on day 2 (Thu), with rises generally near or above the high water
threshold (50% and higher annual exceedance probabilities (AEPs)). However,
there are isolated higher magnitude flows possible on smaller streams given
isolated AEPs at or below 20%, somewhat increasing the confidence in the
potential for localized higher-end impacts. As the system moves into the
Gulf Coast states, it is expected to weaken and rainfall will become more
scattered.

.West...
Daily showers and storms will persist across portions of the Sierra Nevada,
Great Basin, and Rocky Mountains through today and across portions of the
Intermountain West and Northern Rockies through early day 2 (Thu) as
moisture pushes northward across these regions. Widespread flooding impacts
are not expected however, locally robust rainfall rates may generate rapid
rises along small streams in areas of steep terrain, as well as in arroyos,
slot canyons, and normally dry washes. Urban flooding is also possible as
well, especially in areas where training convection materializes. There is
a risk of debris flows and subsequent flash flooding near recently burned
areas.

.Alaska...
A period of wet and unsettled weather is expected to continue across much
of the state, with the heaviest rainfall totals in the south and west of
Fairbanks, through the end of the week. River rises and subsequent flooding
are ongoing across portions of the Upper Koyukuk River basin following
recent rainfall over the past several days. As rainfall continues today,
sharp river rises are expected across the remainder of the Koyukuk and
Kobuk basins. Additional rainfall impacting south-central AK may generate
sharp rises and subsequent flooding along streams and rivers across the
Kenai Peninsula, across the Prince William Sound, and along the Yentna,
Susitna and Skwentna rivers on days 3 - 4 (Fri - Sat).

//DPL





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