026
AGUS74 KWCO 251516
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE JUN 25 2024

.Synopsis...
Additional rounds of rainfall in the Northern Plains and the Upper and
Middle Mississippi Valley... Flash flooding possible in the Four Corners
region, Great Lakes and Northeast...Snowmelt induced flooding continues in
Alaska...

.Discussion...

.Northern Plains and the Upper and Middle Mississippi Valley...
Widespread moderate to major river flooding is ongoing and/or forecast
across southeast SD, southern MN, northern IA and record flooding is
ongoing along the Vermillion, West Fork of the Des Moines, Little Sioux,
and the Minnesota rivers. Many of these rivers are already in recession,
but will remain in flood status well into next week. Additional rainfall is
expected over the next week (1 - 3", NBM), which could exacerbate the
ongoing flooding and delay recessions however, the heaviest totals are
currently forecast to mostly stay in south-central IA, away from the worst
of the ongoing flooding. Topsoils have recovered slightly from last weeks
rain, but are still near saturation (0 - 10 cm RSM, NASA SPoRT), and
rainfall will quickly convert to runoff into streams, rivers, and low-lying
areas. In MN, the Rapidan Dam along the Blue Earth River has breached and
is in danger of a total failure as of Tuesday morning. Multiple levee
failures in IA have also led to additional flooding impacts.

In southern IA, northern MO, and western IL, 2 - 3" of rainfall is
expected, and antecedent conditions are less favorable for runoff compared
to areas further north. That being said, southern IA is somewhat
hydrologically sensitive with topsoils in the 50 - 60% range (0 - 10 cm
RSM, NASA SPoRT) and above average flows (USGS). Within-bank rises to area
streams are likely, and some localized flooding impacts are possible.
Northern MO and western IL are both on the drier side and should be able to
absorb the rainfall without significant flooding impacts. Flash and urban
flooding is possible anywhere heavy rainfall persists or storm training
sets up.

.Four Corners...
Moisture will persist over the region throughout the week, particularly in
parts of NM and AZ, leading to locally heavy rainfall and the potential for
flash flooding. Areas that have recently received rainfall may continue to
face a risk of flash flooding and excessive runoff. The highest flood
threat is in areas with recent burn scars, slot canyons, dry washes, and
regions where training and more persistent storms occur.

.Great Lakes...
Flooding impacts are possible for states along the Great Lakes today as
convective rainfall sweeps across the area. Antecedent conditions are
relatively dry with topsoils generally between 40 - 55% RSM (0 - 10 cm,
NASA SPoRT) and streams running at or below annual mean flows. These
conditions will likely preclude any significant small stream or riverine
response to this rainfall, but high rainfall rates could lead to localized
instances of flash and urban flooding.

.Northeast...
Isolated incidences of flash and urban flooding on day 2 (Wed) and again on
Sat (day 5) remain possible across the region as multiple frontal
boundaries generate scattered showers and storms. Outside of urban areas,
the Adirondacks and northern New England (VT/NH/ME) are most vulnerable to
hydrologic responses given wet soils (60 - 75% RSM, 0 - 10 cm NASA SPoRT)
from recent rainfall. Impacts will be dependent on storm motion and the
intensity of rainfall rates.

.Alaska...
Warming temperatures continue to cause snow and ice melt at high
elevations, leading to rivers running high in areas across Southcentral AK.
Minor flooding on the Chilkat River near Klukwan continues into early this
week. Also, there continues to be high water on the Nuyakuk River near
Dillingham. The Skwentna and Yentna Rivers will also likely have high water
with out-of-bank conditions today.

//Bliss/Pritchard



$$