986
AGUS74 KWCO 192008
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
300 PM CDT SAT SEP 19 2026

...Considerable flooding impacts possible across portions of the Upper
Midwest into the Upper Ohio Valley... Locally considerable flash and small
stream flooding possible for the Northern Rockies into the Northern High
Plains... Locally considerable flash and small stream flooding impacts are
possible across New Mexico... Flooding impacts possible for the Central
Appalachians into the Mid-Atlantic... Isolated flooding impacts through
Thursday for Guam and Rota...

.Upper Midwest into the Upper Ohio Valley...
A Considerable flood threat area remains in place across portions of
northern Illinois into northern Indiana, with an extension west into
southeastern Minnesota following heavy overnight rainfall of 6 - 7"+, where
significant hydrologic responses are already ongoing and moderate to major
river flooding is expected near the tri-state area. Significant river
flooding may also linger into early next week across affected basins.
Surrounding this area, a Limited remains in place across the broader region
where flooding impacts remain possible through Monday.

In the short term, the primary focus is across eastern Iowa, southern
Wisconsin, and northern Illinois, including the Chicago metro area, as well
as the Upper Wabash Basin in Indiana. Topsoils across the region are
saturated and primed for efficient runoff, leaving basins highly sensitive
to additional rainfall. Additional heavy rainfall capable of producing high
rainfall rates could quickly overwhelm remaining infiltration capacity,
leading to significant flash and urban flooding along with sharp rises on
already elevated small streams. The National Water Model (NWM) Short Range
Forecast (SRF) continues to highlight rapid-onset flooding potential across
this corridor, along with higher magnitude streamflow responses, with high
rainfall rates expected to be the primary driver of significant hydrologic
responses.

Through Sunday, the threat for considerable flash, urban, and river
flooding continues across portions of Illinois and Indiana where repeated
rounds of heavy rain may produce efficient runoff, additional sharp stream
rises, and minor to moderate river flooding. HEFS ensemble guidance and NWM
Medium Range Forecasts (MRF) support significant hydrologic responses
across this region, particularly where training convection overlaps the
more sensitive basins.

.Northern Rockies into the Northern High Plains...
Locally considerable flash and small stream flooding is possible through
Sunday across portions of Montana and Wyoming as repeated rainfall occurs
over steep terrain and areas with limited infiltration capacity. This could
lead to rapid runoff and quick rises on small streams and creeks, with
flash flooding and debris flows also possible in the vicinity of burn
scars. In the near term, the NWM SRF highlights rapid-onset flooding
potential across southern Montana, primarily in and around the Billings
area beginning late tonight. Probabilities remain generally modest (less
than 50%), but will likely increase as rainfall continues and is captured
within the 12-hr forecast window.

.New Mexico...
Locally considerable flash flooding is possible beginning Tuesday and
continuing through late week as another surge of monsoonal moisture brings
repeated rounds of thunderstorms and locally heavy rainfall to the region.
Rapid runoff will be possible across small streams, creeks, dry washes, and
mountain canyons, with flash flooding and debris flows also possible in the
vicinity of burn scars and across steep terrain. Both the NBM and
GFS-forced NWM MRF have consistently highlighted the potential for renewed
flooding, although some variability remains in the general placement and
magnitude. Nonetheless, the greatest potential for significant impacts is
likely to be along and east of the Central Mountain Chain, especially
across portions of the Pecos River Valley on Tuesday and Wednesday.

.Central Appalachians into the Mid-Atlantic...
Multiple rounds of rainfall may lead to flooding impacts starting Monday
and continuing through midweek. While antecedent conditions vary across the
region, repeated rainfall will gradually increase runoff efficiency and
could lead to flooding where heavier rainfall occurs. The threat will be
greatest across urban, low-lying, and poor-drainage locations, particularly
where higher rainfall rates occur or bands repeatedly develop over the same
areas. However, given the extended timeframe, uncertainty remains regarding
the placement and magnitude of potential flooding impacts. A Limited flood
threat remains in place across the region, with adjustments made to the
overall selection based on the latest QPF trends.

.Guam and Rota...
Flash and urban flooding is possible through Thursday as tropical moisture
continues to support locally heavy rainfall across the islands.

.Alaska...
Additional rainfall through the remainder of the weekend may produce
localized flooding across portions of the state. Across portions of the
Interior, impacts are expected to remain limited to minor pooling and
ponding in low-lying and flood-prone areas. Farther southeast, heavy
rainfall combined with ongoing snow and ice melt may lead to more notable
rises across portions of the Northern Panhandle. Given the generally
isolated nature of the expected impacts, no FHO areas are warranted.

//Freeman

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