271
AGUS74 KWCO 241524
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT MON JUN 24 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 and Northeast...Snow-melt induced flooding continues in Alaska...

.Discussion...

.Northern Plains and the Upper and Middle Mississippi Valley...
Additional rounds of rainfall continue today through the end of the week
bringing the potential for flash, urban and small stream flooding. Any
rainfall today will likely be on the lighter side and is expected to have
minimal hydrologic impacts while days 2, 4 and 5 will be the heaviest (Tue,
Thu, Fri). Widespread moderate to major river flooding is ongoing and/or
expected across southeast SD, southern MN, and northern IA into next week.
Record forecasts are ongoing and/or forecast for many rivers seen over the
same areas. Soil conditions are still wet in areas of southeastern SD,
northern IA, southern MN and central WI  (0 - 10 cm, 65 - 85% RSM, NASA
SPoRT) given that widespread rainfall amounts of 2 - 5" (MRMS) have fallen
over the past 48 hours. However, given the lull in activity yesterday, some
soil moisture was allowed to recover. Even so, streamflows still continue
to run much above normal for all days of the year, suggesting that while
soils are still wet, there is limited storage capacity to store additional
rainfall and any remaining soil capacity will likely be overwhelmed once
again. Each additional round of rainfall will serve to further compound the
flood potential. The National Water Model (NWM) Medium Range Forecast (MRF)
continues to highlight much of the same region that has just seen past
rainfall including areas of southeast SD, northeast NE, southern MN,
northern IA, and central WI. Rapid-onset flooding probabilities (ROF) are
near 25 - 50% in these areas with corresponding annual-exceedance
probabilities (AEPs) near 50% with more localized probabilities near 20%.
Given these conditions, any given rainfall may delay recessions and may
potentially cause some renewed rises.

.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.

.Northeast...
Moderate to locally heavy rainfall continues to impact the region bringing
the potential for isolated instances of flash and small stream flooding
today and then again on days 3 and 6 (Wed and Sat). Prior rainfall has
primed the region, wetting soils (60 - 75%, 0 - 10 cm, NASA SPoRT) and
elevating streamflows to above normal mean annual streamflow (USGS). Today,
the greatest flood risk lies in southern ME and the northernmost parts of
NY and VT, where the highest rain totals are forecasted (1", with locally
higher amounts). Later in the forecast period, on day 3, the threat shifts
southward, with a bullseye of 2" totals centered between NY and MA. Beyond
that, areas with continuous rainfall, particularly urban areas, are at the
highest risk for flooding.

.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 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.

//Kirkpatrick/Wood



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