262
AGUS74 KWCO 151458
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE JUL 15 2025

.Synopsis...
Isolated flooding potential continues across Central Texas and the
Mid-Atlantic and the Central/Southern Appalachians... Increasing potential
for flooding impacts across the Central Gulf Coast and Florida... Isolated
flooding possible across the Northern Plains in the Midwest, Southwest, and
the Ohio and Tennessee Valleys...

.Central Texas...
Isolated flash, urban, and renewed river rises will remain possible through
this evening as locally heavy rainfall continues over already wet basins.
While the system is expected to gradually weaken throughout the day, the
hydrologic environment remains highly sensitive soils are nearly or fully
saturated, and in-channel storage is limited due to lingering high flows.
Given these conditions, flash and river flooding could develop rapidly with
localized heavy rainfall, and even modest additional rainfall amounts may
trigger renewed flood responses. This is supported by the National Water
Model (NWM) Short-Range Forecast (SRF), which continues to highlight
rapid-onset flooding across portions of the Hill Country, with the
strongest signals occurring between Ozona and Brownwood, some of which is
likely ongoing per the Rapid-Onset Flood Arrival Time Forecast, and some
that are expected to begin later this evening. In addition, higher
magnitude (between 10 - 2%, annual exceedance probability) streamflows can
be seen throughout this area, supporting the potential for isolated, yet
new out-of-bank rises.

.Mid-Atlantic and the Central/Southern Appalachians...
Isolated flash and urban flooding, some locally significant, remains
possible across portions of the region through this evening as additional
periods of locally heavy rainfall develop over already hydrologically
sensitive areas. Of particular concern is eastern VA, where 7-day rainfall
totals of 5 - 10"+ (RFC QPE) have left soils saturated and streamflows
elevated, with little to no recovery time. The NWM SRF is highlighting the
potential for rapid-onset flooding across eastern VA into the NC Piedmont,
however, overall streamflow responses remain modest, likely due to the
convective nature of the rainfall. Nonetheless, flooding impacts will be
possible anywhere training rainfall or intense rainfall rates develop,
especially in urban areas and areas of complex terrain.

.Central Gulf Coast and Florida...
In the short term, flash and urban flooding is likely across portions of
central FL as a low pressure system continues to move onshore, bringing
locally intense rainfall rates of up to 4"/hr and the potential for
localized totals between 4 - 7". Regardless of antecedent conditions, the
expected intensity of rainfall will likely exceed infiltration and drainage
capacities, and flash and urban flooding is expected should these higher
rates materialize. This is supported by the NWM SRF, which is beginning to
highlight the potential for rapid-onset flooding across portions of the
region, with the greatest consistency from Orlando eastward along the coast
from Palm Coast to Palm Bay.

Looking ahead, the potential for flooding impacts continues to increase
across the region as multiple rounds of moderate to heavy rainfall are
expected through the forecast period. Rainfall is expected to range from 2
- 5" (7-day totals), with higher totals of 5 - 7" (locally higher possible)
along the Central Gulf Coast as tropical moisture surges into the region,
bringing a prolonged period of heavy rain, especially across southeastern
LA. Antecedent conditions across this area are more dry, and flooding may
initially be limited by sandy, well-drained soils and generally near-normal
streamflows. However, repeated rounds of rainfall, with efficient warm
cloud processes capable of producing very high rainfall rates, could
eventually overwhelm local infiltration capacity and lead to flooding
impacts.

Across the FL Peninsula, antecedent conditions are wetter following several
days of rainfall, and streamflows are locally elevated, with isolated minor
flooding forecast later this week. While sandy soils and karst topography
will still help absorb initial rounds of rainfall, capacity may be exceeded
more quickly given the existing wet conditions. Urban corridors along I-10
in the Central Gulf Coast and I-95 in FL remain particularly vulnerable to
flash flooding due to impervious surfaces and poor drainage in some areas.

.Northern Plains into the Upper Midwest...
Isolated flash and urban flooding is possible across portions of central MN
and northern WI today and in the Quad Cities region through day 2 (Wed).
Antecedent soil conditions have recovered since the previous rainfall event
(50 - 65% RSM, 0 - 10 cm, NASA SPoRT) however, streams and rivers are
still running higher than normal for this time of the year, suggesting the
hydrologic environment remains somewhat vulnerable, particularly in areas
with flashy responses or limited channel capacity. While widespread
flooding is not expected, isolated flooding impacts cant be entirely ruled
out, especially if higher rainfall rates materialize in urban areas.

After a brief reprieve in rainfall on day 3 (Thu), additional rainfall
returns to the region on days 4 - 7 (Fri - Mon), although each round
appears modest (less than 1.5"), and the placement of the highest QPF each
day does not overlap. However, given the current convective pattern and
differences in model guidance, the exact location and magnitude of any
potential hydrologic responses remain uncertain.

.Southwest...
Isolated flash flooding is possible this week across portions of AZ and NM
as monsoonal moisture increases. Given ongoing drought conditions, rainfall
will be mostly beneficial in this region, but heavy downpours may lead to
flooding over sensitive basins, urban areas, complex terrain, and burn
scars. The greatest potential will be in southeast AZ today and NM on day 3
(Thu). A drying trend is expected to gradually reduce flood potential by
the weekend.

.Ohio and Tennessee Valleys...
A wet weather pattern bringing daily rounds of rainfall through the
forecast period will increase the potential for isolated flooding impacts.
Antecedent soil conditions are generally near normal to slightly wet and
streamflows are near to below normal for this time of the year. Combined
with the expected progressive nature of the convection, this should
initially allow for adequate infiltration. However, each subsequent round
may further increase hydrologic vulnerability, particularly in areas that
experience repeated rainfall. The greatest potential for flooding impacts
will be in areas where high rainfall rates or training storms develop,
which could quickly overwhelm current ground conditions and lead to
enhanced runoff and rising streamflows. For now, confidence in the exact
placement or magnitude of any hydrologic responses remains low given the
extended timeframe.

//Freeman

$$