172
AGUS74 KWCO 031514
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE JUN 3 2025

.Synopsis...
Widespread flooding, including considerable flash and river flooding,
possible across the Central and Southern Plains into the Middle Mississippi
Valley... Isolated urban flooding possible in Florida through the Coastal
Carolinas... Isolated flash and river flooding possible in the Southeast...

.Central and Southern Plains into the Middle Mississippi Valley...
Considerable flash and river flooding is becoming more likely late week
across portions of northeast TX and OK, with locally considerable impacts
also possible in surrounding areas, as a wet weather pattern bringing daily
rounds of rainfall through day 7 (Mon) is expected. Although recent
rainfall has left topsoil layers wet across eastern OK/KS and western MO,
deeper soil moisture conditions (10 - 40 and 40 - 100 cm, NASA SPoRT)
remain near normal across much of the area (up to 70% RSM), suggesting
infiltration capacity remains available, at least early on. However,
initial rounds of rainfall will begin to saturate topsoils and prime the
area for faster runoff, with each additional round of rainfall further
exacerbating the flood potential. Current streamflows are near to above
normal across much of the area, with most gages reporting in the 76th to
90th percentile for historical flows (USGS). This suggests that rivers and
streams have been running higher than usual for some time, reducing the
hydrologic systems ability to absorb additional rainfall and increasing
the potential for widespread small stream and river flooding as the event
continues. The Hydrologic Ensemble Forecasting Service (HEFS) and other RFC
ensemble guidance supports this, projecting widespread minor and isolated
moderate flooding across eastern portions of KS, OK, and TX into western
MO, along with isolated major river flooding in OK (30% chance of
exceedance).

In the short term, the HRRR-forced National Water Model (NWM) Short Range
Forecast (SRF) is signaling the potential for rapid-onset flooding across
primarily eastern KS, with probabilities continuing to slowly increase with
each run. However, these signals may be underdone in both magnitude and
extent due to the relatively fast storm motion of the ongoing convection
and the bulk of the QPF remaining just outside the 12-hour probability
window. Corresponding annual exceedance probabilities (AEPs), per the SRF
High Flow Magnitude, remain mostly at or above 50% overall, with isolated
higher magnitude/lower AEPs (10% - 2%) occurring on some smaller order
streams.

In the medium range, both the GFS- and NBM-forced NWM continue to indicate
widespread stream responses beginning on day 2 (Wed), with isolated higher
magnitude/lower AEPs (10% - 4%), per the NBM High Flow Magnitude forecast,
signaling across central and eastern OK. This remains the primary area of
concern for potential considerable flooding impacts later this week, with
peak flows not expected until day 6 (Sun) for smaller streams, and day 8
(Tue) or beyond for larger mainstem rivers.

.Florida through the Coastal Carolinas...
Isolated urban flooding remains possible through this evening across South
FL, primarily from Homestead to West Palm Beach, as showers and
thunderstorms with high rainfall rates continue across the region.

Further north, isolated urban flooding will be possible along portions of
the Southeast Coast on days 2 - 3 (Wed - Thu) as tropical moisture brings
rounds of locally heavy rainfall. Any flooding impacts should remain
limited to immediate coastal and low-lying urban areas, with riverine
flooding not expected.

.Southeast...
Isolated flash flooding and river may be possible for portions of MS and AL
on days 6 - 7 (Sun - Mon). Recent rainfall has left upper-layer soils
across the region wet but not saturated, allowing for better absorption of
additional rainfall into the system and reducing the overall flood threat.
However, multiple days of rain, as well as periods of higher rainfall
rates, could still lead to some flooding impacts.

//Freeman



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