910
AGUS74 KWCO 211521
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT FRI JUN 21 2024

.Synopsis...
Considerable flooding is possible in the Northern Plains and Upper
Midwest... Flash flooding possible in the Four Corners region... Localized
urban flooding possible in the Northeast... Snow-melt induced flooding in
Alaska...

.Discussion...

.Northern Plains and Upper Midwest...
Flash, urban, and river flooding, with considerable impacts, are expected
today through the weekend from a multi-day storm system bringing repeat
rounds of heavy rainfall across the region. Widespread moderate to major
river flooding is expected across southeast SD, southern MN, and northern
IA this weekend into next week. Many locations along the Mississippi River
will approach flood stage towards next weekend. A brief lull is then
expected on day 3 (Sun) before additional rounds on days 4 - 5 (Mon - Tue),
although this rainfall should be less significant. The heaviest rainfall
(7-day totals) continues to be placed across southeastern SD, southern MN,
and central WI (3 - 5", locally higher possible). Soil conditions are wet
to saturated in areas of eastern SD and southern MN (0 - 10 cm, 80 - 90%
RSM, NASA SPoRT) and streamflows are running much above normal for all days
of the year, suggesting limited infiltration capacity. Given these
conditions, it will not take much rainfall to generate immediate runoff and
subsequent flooding of small streams and creeks, as well as low-lying and
poorly drained locations in urban areas. Each additional round of rainfall
will serve to further compound the flood potential. The National Water
Model (NWM) Short Range Forecast (SRF) is responding accordingly with
widespread responses and the potential for rapid-onset flooding near 25 -
50% with more local responses near 75%. Corresponding annual-exceedance
probabilities (AEPs) below 20% are seen across basins within the
aforementioned region of SD/IA/MN, where high flows are ongoing and
significant river flooding is expected. The Medium Range Forecast (MRF) is
much the same as far as responses, however, AEPs tend to be more aggressive
in the medium-range indicating more out-of-bank rises in the long run..

.Four Corners...
Locally heavy rainfall, bringing the potential for flash flooding in states
surrounding the Four Corners region, will be of concern today, especially
in areas of eastern UT, southwest CO and northern to central NM. The flood
threat is highest in areas on recent burn scars, slot canyons, dry washes
and where training is likely to occur.

.Northeast...
The potential exists for localized flooding impacts in primarily urban
areas today through day 4 (Mon) as showers and thunderstorms develop across
the region. Outside of sensitive urban areas, near normal relative soil
moisture values (50 - 70%, 0 - 10 cm, NASA SPoRT) and near to below mean
annual streamflows (USGS) suggest sufficient infiltration capacity overall
to capture runoff. These factors, combined with modest rainfall amounts
(less than 2", WPC), will help to mitigate any widespread hydrologic
responses and limit the threat to urban, low-lying, and poor drainage areas.

.Alaska...
Warming temperatures continue to cause snow and ice melt at high
elevations, leading to rivers running high in areas across Southcentral
Alaska. Minor flooding on the Chilkat River near Klukwan continues as well
as high water on the Nuyakuk River near Dillingham.

//Kirkpatrick



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