095
AGUS74 KWCO 081637
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
1015 AM CDT TUE JUL 8 2025

.Synopsis...
Locally considerable flooding is possible in the Mid-Atlantic and
Northeast... Isolated flooding possible in the Southern Plains and Lower
Mississippi Valley and the Central Plains into the Upper Midwest...
Isolated flash flooding remains possible in American Samoa...

.Mid-Atlantic and Northeast...
Flash, urban, and small stream flooding, some locally considerable, will be
possible across the Delmarva region into eastern PA, NJ, the coastal
Northeast, and portions of the Central Appalachians today through day 2
(Wed), as well as across much of NC on day 2, as slow-moving storms develop
across the region. Antecedent conditions are variable but generally range
from dry to near normal, with pockets of wetter soils and locally elevated
streamflows due to recent rainfall. Nonetheless, the combination of urban
sensitivities, slow storm motion, and locally intense rainfall rates may
quickly overwhelm topsoil capacity, enhancing runoff and leading to rapid
rises on small streams, creeks, and urban drainages. Locally significant
urban flooding impacts may develop if heavier rainfall focuses over the
urban corridor from Delmarva to MA, or across the steep terrain of the
Central Appalachians. While widespread small stream and river flooding is
not expected, the NWM continues to highlight potential for at least
isolated rapid-onset flooding, however, SRF 12-hour rapid-onset flooding
probabilities remain below 25%, largely due to current runs of the HRRR
underperforming in the east.

Additional rounds of rainfall are expected across much of the region during
days 3 - 7 (Wed - Mon), bringing a renewed threat of flooding impacts.
While daily rainfall totals are generally expected to remain below 2",
repeated rounds of precipitation may further increase hydrologic
vulnerabilityespecially where rainfall repeats over the same areas.

.Southern Plains and Lower Mississippi Valley...
Isolated flash, urban, and small stream flooding is possible through this
evening across eastern OK, western AR, and southern MO as showers and
thunderstorms continue to impact the region. Current radar data and trends
indicate this convection is slow-moving and contains intense rainfall
rates. Even with relatively normal to slightly elevated topsoils, these
high rain rates, as well as overall rainfall amounts, will be able to
overcome remaining soil infiltration capacity, leading to quick runoff into
already elevated streams, especially given the complex terrain. The
National Water Model (NWM) Short Range Forecast (SRF) is signaling the
potential for rapid-onset flooding within the next several hours, although
12- hour probabilities remain below 25% due to the NWM being slow to pick
up on the convection. However, the latest HRRR is coming in line with
observations, resulting in the deterministic run of the NWM likely to
increase probabilities for rapid-onset flooding.

.Central Plains into the Upper Midwest...
Isolated flash and urban flooding is possible on days 3 - 4 (Thu - Fri),
primarily across IA and MN where the heaviest rainfall (up to 2", locally
up to 4") is forecast. While antecedent conditions are generally primed,
fast storm motion and relatively low QPF totals should help limit any
significant flooding concerns. Still, isolated instances of flooding can`t
be ruled out, especially if training rainfall develops.

.American Samoa...
Isolated flash flooding remains possible through at least this morning
(local time) as additional rounds of locally heavy rainfall continue to
develop over the island.

//Freeman



$$