309
AGUS74 KWCO 142027
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
300 PM CDT MON SEP 14 2026

...Considerable flooding impacts likely by mid week across the Central Plains
into the Upper Great Lakes... Isolated flash and urban flooding impacts are
possible throughout the week across the Southwest... Isolated flooding
impacts possible in Alaska...

.Central Plains into the Upper Great Lakes...
Considerable flash and river flooding impacts will be possible this week as
successive days of rainfall (5 - 7" WPC QPF Days 1 - 5) impact the region.
The initial round is expected tonight over southern Iowa. Rainfall totals
of 2 - 3" with locally higher amounts will be possible (HRRR). The
HRRR-forced National Water Model (NWM) Short Range Forecast (SRF) is
starting to show stream responses in southwest IA from Omaha to Des Moines
with streams beginning to respond later this evening and continuing through
the overnight hours. This rainfall will likely prime the region ahead of
additional rounds of rainfall through the week.

Looking ahead in the forecast, flash and urban flooding will be possible
through the week along with an increasing threat of river flooding. Both
the GFS- and NBM-forced NWM Medium Range Forecasts (MRF) are showing robust
streamflow responses across southern IA. The NBM version even shows more
robust and widespread signals stretching into northern MO and into MN/WI.
Additionally, HEFS (30% exceedance) continues to indicate
isolated-to-scattered moderate-to-major river flooding across the region
suggesting the potential for significant river flooding. Despite the strong
signals, there remains some uncertainty and much of the potential for
impacts is predicated on where these rounds of rainfall overlap.
Nevertheless, this region needs to be closely monitored over the next
several days.

.Southwest...
Isolated flash and urban flooding impacts are possible throughout the week,
especially in the vicinity of steep terrain and recently burned areas. The
HRRR indicates scattered showers with  .5" - 2" of rainfall totals across
New Mexico this evening which is driving isolated stream response from the
NWM SRF. The SPoRT LIS 0 - 10cm relative soil moisture index indicates
localized Relative Soil Moisture up to 65% in some places across the
southwest already. The region is expected to remain in an active rainfall
pattern through the week which is reflected by the NWM MRF. The NWM MRF
(both GFS and NBM forced versions) continues to indicate potential for
fairly widespread small stream responses in headwater basins draining the
terrain of the eastern slopes of the Black Range Mountains, the San Andres
Mountains, and the Sangre de Cristo Mountains in NM by mid week.

This is a fairly robust and uncommon signal from the NWM for this part of
the country, so trends will need to be monitored closely as we head into
the week.

.Alaska...
Heavy rain is forecast today and is expected to continue through Wednesday.
(Lower Koyukuk Valley-Lower Yukon and Innoko Valleys-Lower Yukon
River-Middle Yukon Valley). Rainfall totals between 1 - 2" are expected
today. With already saturated ground conditions across the region (Variable
locations 65%, 0-10cm Relative Soil Moisture SPoRT). Mainstem river
flooding is not expected, but highwater flows and bankfull conditions are
likely through the week as area rivers respond. Localized flooding on
smaller creeks and streams are likely.

//RK/Smith

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