054
AGUS74 KWCO 241518
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE JUN 24 2025

.Synopsis...
Considerable flooding expected, locally catastrophic flooding possible
today in portions of New Mexico and Southwest Texas... Flash and river
flooding possible through late week in the Central Plains and Mid to Upper
Mississippi Valley... Snowmelt runoff continues to cause flooding concerns
in portions of Alaska... Flash flooding possible later this week across the
Mariana Islands...

.New Mexico and Southwest Texas...
Considerable to locally catastrophic flooding is expected across portions
of NM through early day 2 (Wed), primarily near recently burned areas. The
highest rainfall amounts today are expected across portions of south
central and north central NM (2 - 4"). Locally higher amounts are possible
in these areas due to the convective nature of the rainfall. Low water
crossings, arroyos, and areas of steep or complex terrain will also be
particularly vulnerable to locally considerable flooding.

Beyond those areas under the highest threat, flash and urban flooding is
possible across much of southwest TX and surrounding areas of NM today
through day 2 (Wed) due to multiple rounds of rainfall. The National Water
Model (NWM) Medium Range Forecast (MRF) (NBM and GFS forced) continues to
signal the potential for high water conditions in portions of the Middle
Rio Grande Valley as well as streams draining the Sangre de Cristo
mountains. Associated MRF annual exceedance probabilities are below 10% for
some reaches, suggesting the potential for significant flows in normally
low flow channels.

.Central Plains and Mid to Upper Mississippi Valley...
Multiple rounds of convective rainfall will bring the potential for flash
and river flooding to eastern NE, eastern SD, IA, southern MN, and WI early
day 4 (Fri). The flood forecast has changed little in the leadup to this
event, with observed rainfall yesterday slightly less than expected and
forecast widespread totals of 2 - 4" locally up to 5" expected. Ahead of
this event, topsoils are generally drier in NE and SD compared to those in
MN, IA, and WI (NASA SPoRT). Additionally, rivers in southern MN and IA
remain above the action threshold leading into this event, along with above
to much above normal streamflows (USGS). Based on these antecedent
conditions, MN, IA, and WI appear to generally be more susceptible to
flooding impacts from this event. The NWM MRF supports that susceptibility,
as both GFS and NBM-forced versions indicate the potential for rapid onset
flooding across IA, southern MN, and WI, and even further west into eastern
NE. Areas that receive multiple rounds of precipitation will be most
vulnerable, making IA and southern MN the best candidates for potential
flooding impacts. River ensemble forecasts (HEFS) also indicate potential
for minor river flooding across much of IA and southern MN at the 30%
chance of exceedance. Given some model trends, locally significant flooding
could be possible, especually in urban areas and basins where heavy
rainfall aligns with local basins. However, with current guidence slow to
catch on and the 10% exceedence of the HEFS most likely being severly
overdone, confidence in location is low.

.Alaska...
Snowmelt continues to lead to high water levels and minor flooding on
various rivers across the state, and this will remain the case as long as
temperatures remain warm. The Chilkat River near Klukwan remains in minor
flood stage and is expected to remain above flood stage through day 2
(Wed). High water levels continue along the Yentna and Skwentna rivers in
the Western Alaska Range and the Matanuska River near Butte. Minor flooding
impacts remain possible along these rivers.

.Mariana Islands...
Heavy rainfall (5 - 10") beginning as early as late on day 3 (Thu) and
continuing through day 6 (Sun) from monsoonal flow could produce flash
flooding across the islands.

//GKendrick

$$