018
AGUS74 KWCO 081524 RRA
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
915 AM CST WED JAN 8 2025

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

.Discussion...

.Alaska Panhandle...
An atmospheric river will move into AK 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.

.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.

East Texas and the Gulf Coast...
Moderate to heavy rainfall of up to 2.5" with locally higher totals is
forecast for areas of East Texas through the Gulf Coast on days 2 - 3 (Thu
- Fri), bringing the potential for localized flooding impacts. Top soils
are around average (55 - 65% RSM, 0 - 10cm, NASA SPoRT) and streamflows are
normal (USGS), suggesting there is infiltration capacity available. In the
South however, colder temperatures resulting in partial ground freezing
could potentially offset some of the infiltration capacity and make surface
runoff more likely, and therefore increase flooding impacts.

.American Samoa...
Flash and small stream flooding is possible through day 3 (Fri).
Additionally, landslides, mudslides, and/or rockslides are also possible in
areas of steep terrain.

//Ducre



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