990
AGUS74 KWCO 091511
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
915 AM CST THU JAN 9 2025

Synopsis...
Localized flooding impacts possible in Southeast Texas and the Gulf
Coast...River rises possible in Alaska...Ice jams possible in the Missouri
River Basin...Flash and small stream flooding possible in American Samoa...

.Discussion...

Southeast Texas and the Gulf Coast...
Moderate to heavy rainfall of up to 2.5" with locally higher totals is
forecast for the region with some of the higher totals across the southeast
TX coast today, bringing the potential for localized urban flooding and
isolated river rises. Rainfall is starting to expand across the region and
is expected to increase in coverage and intensity through the afternoon and
into the early part of day 2 (Fri). Soils are near normal (55 - 65% RSM, 0
- 10cm, NASA SPoRT) and streamflows are near normal (USGS), suggesting
there remains some infiltration and channel capacity available which will
help to mitigate any widespread flooding impacts. Most of the rainfall is
captured in the HRRR-forced National Water Model (NWM) Short Range Forecast
(SRF) and responses have been modest overall, particularly for rapid-onset
flooding However, the existing responses suggest rises on some of the area
rivers will be possible including minor river flooding. This is suggested
in both the NBM-forced NWM and the river ensemble forecasts (HEFS, SR QPF
Ensembles). The latest RFC forecasts indicate new minor river flooding
across the Sabine and Neches River basins. Urban flooding will also be
possible, particularly near coastal areas where the heaviest rainfall is
expected.

.Alaska...
An atmospheric river will move into the AK Panhandle this week, bringing
heavy rainfall of up to 3" with locally higher totals through Friday. The
influx of warmer temperatures will also raise the snow levels of the area
between 4000 - 5000 feet, increasing runoff amounts from snowmelt as well
as decreasing the likelihood of snowfall in lower elevations. The
combination of rainfall and snowmelt runoff will prime hydrologic
conditions in the area and possibly allow for significant river rises.

Across the Kenai Peninsula north into the Mat-Su Valleys, recent and
continuing warm weather and widespread rainfall have led to rising creeks
and streams. This could create ice movement and lead to ice jam flooding.



.Missouri River Basin...
An extended period of frigid temperatures across the lower Missouri River
basin continues and could potentially exacerbate ongoing low flows on the
Missouri River and smaller tributaries. The Missouri River at Omaha (NE),
near Blair (NE), and at Sioux City (IA) is either below the low flow
threshold or within a few feet of the threshold, suggesting that any ice
blockage upstream could drive the river at those locations even lower and
result in impacts due to low flow conditions. Additionally, some of the
smaller tributaries and headwaters near low flow thresholds could also be
impacted.

Conversely, areas upstream of any jams can expect rises and the potential
for ice jam-induced flooding, particularly on any streams or rivers running
normal to above normal.

.American Samoa...
Flash and small stream flooding is possible through day 2 (Fri).
Additionally, landslides, mudslides, and/or rockslides are also possible in
areas of steep terrain.

//Smith



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