421
AGUS74 KWCO 301523
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
915 AM CST THU JAN 30 2025

.Synopsis...
Flood potential continues for Southern Plains into the Tennessee Valley and
Kentucky and West Virginia... Localized flooding possible tonight in
Northeast KS into Northwest MO... Prolonged rainfall and flood potential
along the West Coast... Flash flooding remains possible through Friday in
Hawaii... Rain on frozen grounds poses a low potential for isolated
flooding concerns across the Middle Mississippi River Valley and Upper
Great Lakes...

.Discussion...

.Southern Plains into the Tennessee Valley...
Widespread moderate-to-heavy rainfall (2 - 4"+, WPC) and isolated flooding
impacts are expected from east TX through the TN Valley through tonight.
Soil moisture across this region has increased from where it was yesterday
at 50 - 70% RSM (0 - 10 cm, NASA SPoRT), but is not yet saturated in most
areas and should be able to handle a good bit of runoff. Nonetheless,
northeast TX through AR is seeing a prolonged period of moderate-to-heavy
rainfall and infiltration capacity is expected to be exceeded with
scattered minor and isolated moderate river flooding beginning today and
continuing over the next couple of days.

Consistent National Water Model (NWM) Short Range Forecast (SRF) responses
are being observed from the DFW area through central and northern AR.
Probabilities for rapid onset flooding are highest across west-central and
northern AR where basin average probabilities are 75 - 100% between I-30
and I-40 in western AR and just north of Little Rock. Peak flows on small
tributaries can be expected late morning through early afternoon according
to the NWM, except in northeast TX where peak flows are either ongoing or
expected through the morning hours. Forecast max flow magnitudes struggle
to reach 20% AEP, suggesting widespread significant river flooding is not
expected. The river flooding potential will increase tonight into tomorrow
morning across the lower OH River Valley, where the NWM SRF is showing
potential for rapid onset flooding across southern IN/IL/western KY.

.Kentucky and West Virginia...
Rain (1 - 2.5" through day 2 (Fri) WPC), warmer temperatures, and above
freezing dewpoints are pushing into the region and will continue through
day 2 (Fri). The higher dewpoints, warming temperatures, and windy
conditions across WV will lead to snowmelt (1 - 2", SNODAS), primarily on
day 2 (Fri). The combination of rainfall and snowmelt will produce total
liquid runoff of 2 - 4"+ and likely produce efficient responses on area
streams and rivers. MMEFS (NAEFS and GEFS) are showing potential for
isolated moderate-to-major river flooding across both states, and QPF and
snowmelt totals going into the ensemble runs looks to be reasonable, so
locally significant river flooding cannot be ruled out, especially across
northern WV where snowmelt will be a significant factor. Recent runs of the
NWM have also shown potential for locally significant river responses
(flows with AEPs around 10%) across WV, however, this signal has not been
consistent.

.Northeast KS into Northwest MO...
Slow moving moderate rainfall (1 - 2", WPC) in the Topeka, KS to Kansas
City, MO region late tonight into tomorrow morning will introduce an
isolated flooding threat. Top layer soils are fairly wet (70 - 85% RSM, 0 -
10 cm, NASA SPoRT), however streamflows are generally still below
climatological normals (USGS), so this should help mitigate most of the
riverine flood threat and restrict most of the flooding potential to the
urban areas of Topeka and Kansas City. Nonetheless, the NWM SRF is showing
some isolated potential for riverine response on smaller tributaries, so
isolated small stream flooding cannot be completely ruled out.

.West Coast...
An atmospheric river will impact much of the west coast beginning on day 2
(Fri) and continuing through the weekend. The primary area of interest
continues to be northern CA where rainfall totals for the event may get as
high as 5 - 10" (7-day QPF, WPC). A lack of rainfall over the last several
weeks has allowed soils to dry to normal levels (50 - 60 % RSM, 0 - 10 cm,
NASA SPoRT), which should allow for decent rainfall infiltration. A
majority of streamflows in the area are well below normal to normal and
channels should be able to handle excess runoff (USGS). As these conditions
do not support widespread flooding conditions, the main concerns for the
next few days will be urban flooding with localized flooding possible as
rainfall continues into early next week. River flooding will become more of
a concern across northern CA by the end of the weekend, when the potential
for mainstem river flooding will increase. This is supported by HEFS 30%
exceedance forecasts showing the Sacramento and Russian River basins
potentially responding into minor flood or higher. Trends continue to
slowly show an increase in flooding potential across northern CA, and
messaging may need to be amplified as we head into the weekend.

.Hawaii...
Isolated flooding will be possible across all islands through Friday.

.Middle Mississippi River Valley and Upper Great Lakes....
Rainfall (1 - 1.5", WPC) atop frozen ground will produce efficient runoff
and introduce an isolated flooding potential from eastern IA into northern
IN through day 2 (Fri).

//JEC





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