763
AGUS74 KWCO 221523
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT SAT JUN 22 2024

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

.Discussion...

.Northern Plains and Upper Midwest...
Flash, urban, and river flooding, with considerable impacts, are expected
to continue today from a multi-day storm system bringing repeat rounds of
heavy rainfall across the region. As there is a brief lull in activity on
day 2 (Sun), additional rounds of rainfall continue early next week with
heavier rainfall forecast on day 7 (Fri). Widespread moderate to major
river flooding is expected across southeast SD, southern MN, and northern
IA this weekend into next week. Record forecasts are ongoing and/or
forecast for many rivers seen over areas of southeast SD and northern IA.
Soil conditions are saturated in areas of southeastern SD, northern IA,
southern MN and central WI  (0 - 100 cm, 75 - 90% RSM, NASA SPoRT) and
streamflows are running much above normal for all days of the year,
suggesting limited to no storage capacity to store additional rainfall and
any remaining remaining soil capacity will likely be overwhelmed. 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 10% 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 indicating continued significant
hydrologic rises through the period..

.Four Corners...
Locally heavy rainfall, bringing the potential for flash flooding, will
continue to shift west of the Rio Grande in NM into areas of AZ. Areas that
received past rainfall may continue to see a threat of flash flooding and
excessive runoff today. The flood threat is highest in areas on recent burn
scars, slot canyons, dry washes and where training is likely to occur.

.Northeast...
Moderate to heavy rainfall continues to impact the region bringing the
potential for localized flash flooding in primarily urban areas today
through day 3 (Mon) and then again on day 5 (Wed). Soils are near normal
(55 - 75%, 0 - 10 cm, NASA SPoRT) and near to below mean annual streamflows
(USGS) suggesting there is still 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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