858
AGUS74 KWCO 191517
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
915 AM CST SUN JAN 19 2025

.Synopsis...
Rapid river ice development likely in the Upper Great Lakes...Potential ice
jams and low-flow impacts across the Missouri River Basin...Rainfall to
return to portions of the Lower Mississippi/Ohio Valleys and the Southeast
mid to late next week...

.Discussion...

.Upper Great Lakes...
Below freezing temperatures will persist through at least early next week
across the region, generating conditions favorable for rapid ice
development on rivers. The greatest concern is along the Rock, Fox, Des
Plaines, and Kankakee rivers in northern IL and IN where freeze up ice jams
are possible. These jams may lead to river rises and isolated areas of
flooding.

.Missouri River Basin...
Cold temperatures are expected to continue through mid-week across the
Lower Missouri River Basin, potentially worsening ongoing low flows along
the mainstem Missouri and tributaries. Of greatest concern is the Missouri
at Omaha (NE), near Blair (NE) and at Sioux City (NE) as these locations
remain near/below the low-flow thresholds. Ice blockages may exacerbate
ongoing low flows in this region. Conversely, river rises and isolated
instances of ice jam induced flooding are possible upstream of these
blockages, especially on streams currently near or above climatological
normals for this time of year.

.Lower Mississippi/Ohio Valleys and the Southeast...
Guidance from both the GFS and NBM-forced National Water Model (NWM) is
indicating the potential for small steam responses on days 8 - 10 in
response to periods of moderate to locally heavy rainfall. Corresponding
annual exceedance probabilities (AEPs), per the High Flow Magnitude
forecast, are indicating the potential for impactful stream rises (AEPs
down to 10%), although given the extended nature of the forecast, the
placement and magnitude of these responses remain uncertain. Several days
of dry weather ahead of this rainfall should allow for soils to recover
from recent rainfall/snowmelt (outside of urban areas), but these regions
should be monitored over the next week.

//Pritchard



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