459
AGUS74 KWCO 021521
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE JUL 2 2024

.Synopsis...
Renewed flooding, isolated flash flooding possible this week for the Upper
and Middle Mississippi Valley... 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, northern IA and MO and is forecast through this week along the
Missouri (moderate) and Mississippi (moderate to major) river mainstems.
Rainfall continues across the region through day 3 (Thu), though light
rainfall could persist through day 6 (Sun). Ample deep layer soil moisture
remains in place across southeastern SD, southern MN, IA, and WI (60 - 75%
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 the next 7 days (thru Mon). At the
minimum, this rainfall will likely cause delayed recessions of ongoing
flooding and isolated flash flooding.

Given those conditions, river flooding is also possible, including the
potential for new and renewed rises at moderate and/or major flood stage
(HEFS, CR Ensemble QPF hydrographs) if heavier rainfall totals occur. The
National Water Model (NWM) Short Range Forecast (SRF) as well as Medium
Range Forecast (MRF), continue to indicate rapid-onset flooding
probabilities generally between 25 - 50% with corresponding annual
exceedance probabilities between 4 - 20% on many smaller tributary rivers
across the aforementioned region. With ongoing flooding and wet soils,
significant impacts cannot be ruled out.

.Four Corners Region...
Daily convection will continue to bring the potential for isolated
significant flash flooding in arroyos, slot canyons, dry washes, urban
areas, and recently burned regions. This potential will persist through the
end of the week, with the highest chances occurring through day 2 (Wed),
particularly in NM, southeastern AZ, and eastern CO. Locations that have
received multiple rounds of rainfall over the past week are most
susceptible to new flooding impacts.

.Puerto Rico...
Showers and thunderstorms through this evening across Puerto Rico will
bring 1 to 2 inches of rainfall, with 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 2 and 3 (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"). Later in the forecast period, on day 6 (Sun),
another heavy round of rainfall will affect southern AK (1 - 2"). This
could lead to rapid rises on streams and rivers, potentially leading to
flooding in affected areas.

//Wood/Kirkpatrick



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