918
AGUS74 KWCO 011512
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT MON JUL 1 2024

.Synopsis...
Renewed flooding, isolated flash flooding possible this week for the Upper
and Middle Mississippi Valley... Isolated flash flooding possible in
portions of the Southeast... Daily convection continues across the Four
Corners Region... Isolated heavy rainfall through Tuesday across portions
of Puerto Rico as Hurricane Beryl tracks south of the island... Increased
snowmelt and glacier runoff, heavy rainfall expected in Alaska...

.Discussion...

.Upper and Middle Mississippi Valley...
Moderate to major river flooding is ongoing across far southeast SD,
southern MN, and northern IA and is forecast through this week along the
Missouri (moderate) and Mississippi (moderate to major) river mainstems.
Rainfall returns to the region today and lingers through day 4 (Thu),
though light rainfall could persist through day 7 (Sun). Ample deep layer
soil moisture remains in place across eastern SD, southern MN, IA, and WI
(60 - 80% RSM 0 - 100 cm NASA SPoRT), suggesting that the already
elevated/flooded rivers across the region will likely respond fairly
efficiently to the runoff from the additional rainfall. Generally 2 - 4"
inches of rainfall is expected across the area through day 5 (Fri). At the
minimum, this rainfall will likely cause delayed recessions of ongoing
flooding and isolated flash flooding.

Given those conditions, river flooding is possible, including the potential
for new and renewed rises above moderate and major flood stage (HEFS, CR
Ensemble QPF hydrographs) if heavier rainfall totals occur. The National
Water Model (NWM) Medium Range Forecast (MRF), both the NBM and GFS-forced
versions, continue to indicate potential for widespread new and renewed
river rises in response to this rainfall with peak flows mostly on days 3 -
6 (Wed - Sat) across southern MN, IA, and WI. The magnitude of response is
still uncertain, but the NWM MRF is indicating potential for 4 - 20% AEP
flows on many smaller tributary rivers across the aforementioned region.
With ongoing flooding and saturated soils, significant impacts cannot be
ruled out.

.Southeast...
Isolated flash and small stream flooding is possible across portions of
northern FL, southern GA, and coastal SC through day 2 (Tue). With normal
to below normal streamflows (USGS) in place and mid-layer soils dry (less
than 50% 10-40 cm RSM, NASA SPoRT), river flooding is not expected.
Top-layer soils are wettest across portions of northern FL but are
otherwise dry across those areas this leaves flash/urban flooding as the
most likely flood mode, especially if intense rainfall rates occur.

.Four Corners Region...
Daily convection will continue to bring the potential for isolated
significant flash flooding in arroyos, slot canyons, dry washes, urban, and
recently burned areas. The potential will persist through the end of the
week, but the best chances will be through day 3 (Wed). Locations that have
received multiple rounds of rainfall over the past week are most
susceptible to new flooding impacts.

.Puerto Rico...
Moderate to heavy rainfall (1 - 4") through Tuesday across southeast Puerto
Rico will bring the potential for isolated flooding impacts. Streamflows
across this portion of the island are generally normal to above normal in
comparison to both the daily and annual climatological normals (USGS), and
soils range from dry to wet but not saturated (NASA SPoRT). Considering
these antecedent conditions and the convective nature of the rainfall,
flooding impacts should remain isolated.

.Alaska...
Recent warm temperatures continue to lead to increased snowmelt and glacier
runoff, leading to elevated flows and minor flooding on a few rivers in
southern AK. Minor flooding along the Chilkat River near Klukwan continues,
and elevated flows continue along the Klutina River near Copper Center and
the Nuyakuk River northeast of Dillingham.

On days 3 and 4 (Wed and Thu), heavy rainfall is expected across western
portions of the Brooks Range (2 - 4") and portions of the Interior,
including Fairbanks (1 - 2"). This could lead to rapid rises on streams and
rivers and flooding cannot be ruled out.

//Watson

$$