681
AGUS74 KWCO 161501
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT WED JUL 16 2025

.Synopsis...
Potential for flooding impacts along the Central Gulf Coast and the Ohio
Valley into the Mid-Atlantic... Isolated flash and urban flooding possible
across the Central Plains and Upper Midwest... Isolated flash flooding
possible across the Southwest into the Rockies...

.Central Gulf Coast...
There is an increasing potential for flooding impacts on days 2 - 3 (Thu -
Fri) as tropical moisture surges into the region, bringing heavy rainfall
totals of 2 - 5", with locally higher amounts possible in southeast LA.
Antecedent conditions leading into this event are dry to near normal, and
any flooding should be initially limited by the regions sandy,
well-drained soils and the ability to absorb early rounds of rainfall, as
well as by the ample storage capacity remaining in area streams and rivers.
However, repeated rounds of rainfall capable of producing very high
rainfall rates could eventually overwhelm local infiltration capacity and
lead to flooding impacts, most likely of the flash and urban variety. Urban
corridors along I-10 remain vulnerable to flash flooding due to impervious
surfaces and poor drainage in some areas. Nonetheless, there is still a lot
of uncertainty around the placement and development of the tropical
moisture, which will influence where the heaviest rainfall occurs and how
the event evolves.

.Ohio Valley into the Mid-Atlantic...
A wet weather pattern bringing daily rounds of rainfall will maintain the
potential for flooding impacts through the forecast period. Rainfall totals
of 2 - 4" are expected, with locally higher amounts possible. Antecedent
conditions are unusually wet for this time of year from eastern VA into NJ,
with NASA SPoRT indicating soil moisture percentiles above the 95th
percentile (0 - 40 cm) and streamflows running much above normal (USGS).
This combination suggests a primed hydrologic environment with limited
capacity for additional runoff, especially where high rainfall rates or
repeated storms occur. In the short term, this is supported by the National
Water Model (NWM) Short Range Forecast (SRF), which is starting to
highlight the potential for at least isolated rapid-onset flooding, with
the strongest signals occurring in the Delmarva region, beginning late
tonight.

In contrast, the remainder of the region ranges from near normal to
somewhat wet, which will initially allow for some infiltration and storage
capacity, though hydrologic sensitivity will increase with each successive
round of rainfall. Overall, widespread flooding is not expected, but the
greatest potential for flooding will be where storms train or become
slow-moving, especially in urban areas or complex terrain.

.Central Plains and Upper Midwest...
Isolated flash and urban flooding is possible today, primarily across WI,
where the heaviest rainfall is forecast. Antecedent conditions are wet but
not saturated, and combined with fast storm motion and relatively low QPF
totals, will limit any significant flooding concerns. However, isolated
instances of flooding cant be ruled out, especially if training rainfall
or high rainfall rates develop. This is supported by the NWM SRF, which
highlights the potential for isolated rapid-onset flooding in central WI,
with the strongest signals occurring in and just east of La Crosse later
this afternoon.

After a brief reprieve in rainfall on day 2 (Thu), additional rounds return
to the region on day 3 (Fri) and continue through the forecast period. Each
daily round appears modest (less than 2"), and the placement of the highest
QPF each day does not overlap. As such, significant or widespread flooding
is not expected at this time.

.Southwest into the Rockies...
Isolated flash flooding is possible through day 2 (Thu) as monsoonal
moisture increases. While rainfall will generally be beneficial, localized
heavy downpours may lead to flash flooding in sensitive basins, urban
areas, and burn scars. The greatest potential will be along the Front Range
and Sangre de Cristo mountains (CO/NM), where conditions will be most
favorable for higher rainfall totals.

//Freeman



$$