946
AGUS74 KWCO 271523
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT THU JUN 27 2024

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

.Discussion...

.Central Plains and the Upper and Middle Mississippi Valley...
Widespread moderate to major river flooding is ongoing and/or forecast
across southeast SD, southern MN, and northern IA. Record flooding is
ongoing and forecast along the Minnesota and Des Moines rivers. Much of the
ongoing major river flooding is in recession. However, as the flood wave
routes downstream and additional rainfall is forecast, flooding impacts on
mainstem rivers, including the Mississippi and Missouri rivers, are still
to come.

An additional 1 - 3" of rain is expected through day 2 (Fri) over portions
of the northern Plains into the Midwest. As soil is already saturated (70
- 90% RSM, 0 - 10 cm RSM, NASA SPoRT), any rain that falls within the
Missouri and northern Mississippi basins, will most likely runoff into
already swollen streams and rivers. Though this amount of rainfall will
most likely not have a major impact, it will allow moderate to major river
flooding to persist, and new localized flooding impacts can be expected.

Over the Central Plains, up to 3" of rain is expected through tomorrow
morning near the Kansas-Nebraska line. Though this may cause isolated
instances of urban flooding, rural flash, and small stream flooding are not
expected as soils in the area are rather dry (less than 50%, RSM, 0 - 10 cm
RSM, NASA SPoRT), and streams are below normal (USGS).

There is potential for locally heavy rainfall forecast day 5 (Mon) across
MN and northern IA. This area will have some time to recover from ongoing
impacts before this next event but will need to be monitored closely, given
the vulnerable antecedent conditions.

.Four Corners...
Moisture will persist over the region throughout the week, particularly in
parts of NM, AZ, and western CO, leading to locally heavy rainfall and the
potential for flash flooding. Areas that receive multiple rounds of
rainfall are more susceptible to flooding impacts as soils reach
saturation. 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 heavy rainfall on day 3 (Sat) will bring the potential for
isolated flash and urban floodings to portions of the Adirondacks and
northern New England. Soils are generally wet closest to the Canadian
border (65 - 75% RSM, 0 - 10 cm NASA SPoRT), making this region more
susceptible to flash flooding. Though areas to the south are somewhat
drier, if heavy rainfall occurs, soils will not take long to become near
saturated, increasing the threat of flooding. The latest GFS-forced NWM MRF
has started to indicate the potential of rapid onset flooding over the
Adirondacks and northeast along the Canadian border. These signals are
generally for lower-order streams, where AEPs are generally around 20%.
This suggests that though streams may see a rapid rise, flows will likely
not significantly increase, especially on higher-order streams.

.Southeast...
Daily scattered precipitation through the weekend will bring the potential
for isolated flash and urban flooding to the region, with the highest
potential being over southern LA/MS though FL/GA/SC. This area is generally
dry, suggesting that flooding impacts will generally be mitigated and
rainfall will be beneficial. However, given how soils have reacted to
recent rainfall over AL (NASA SPoRT), both urban and flash flooding is not
out of the question if training occurs.

.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, with ample snow available to melt. Minor river flooding is expected
on the Skwentna and Yentna Rivers through the week. Also, high water
continues on the Nuyakuk River near Dillingham.

//GKendrick


$$