122
AGUS74 KWCO 091520
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
10:15 AM CDT WED JUL 9, 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...

.Mid-Atlantic and Northeast...
The primary hydrologic concern on Day 1 (Wed) is the potential for flash
flooding across central to southeastern Virginia, the DelMarVa Peninsula,
and North Carolina. While widespread river flooding is not expected,
locally considerable urban flooding impacts are possible. Antecedent
rainfall from the past 24 hours, of 1 to 2 inches with localized totals
near 3 inches, has increased soil moisture and elevated the potential for
excessive runoff. Thunderstorms are expected to produce intense rainfall
rates of 1 to 2 inches per hour, according to the High-Resolution Rapid
Refresh (HRRR), leading to rapid rises on smaller streams and creeks.
However, some model guidance indicates uncertainty in whether these storms
will maintain intensity as they reach the immediate coast, which may temper
the hydrologic response in those specific areas.

While the National Water Model (NWM) shows potential for isolated
rapid-onset flooding, the corresponding Short-Range Forecast (SRF)
probabilities remain below 25%, likely reflecting a known underperformance
of the HRRR model in this pattern. SRF maximum high flow magnitude values
are variable, ranging from 10% to 50% in scattered locations throughout the
region. Looking ahead to days 2 - 6 (Thu - Mon), additional rounds of
rainfall are forecast. Although daily totals may be modest, repeated
precipitation over the same basins could increase hydrologic vulnerability
and renew the threat of flooding.

.Southern Plains and Lower Mississippi Valley...
The primary hydrologic concern is the potential for isolated flash flooding
during days 4 - 5 (Sat - Sun) across eastern Oklahoma, western Arkansas,
and southern Missouri. The reason for this threat is the possibility of
slow-moving thunderstorms with intense rainfall rates developing over an
area with complex terrain. Antecedent conditions, including near-normal but
slightly elevated soil moisture and some already elevated streams, could
enhance runoff. According to the Weather Prediction Center (WPC), while
there are discrepancies between the Global Forecast System (GFS) and the
National Blend of Models (NBM) as to the location of the greatest
precipitation, this reflects typical forecast uncertainty at this range.
Regardless of the exact placement, any high-intensity rainfall could
overwhelm local infiltration capacity, leading to rapid rises on smaller
streams and urban flooding.

.Central Plains into the Upper Midwest...
Isolated flash and urban flooding is possible on days 2 - 3 (Thu - Fri),
primarily across IA and MN where the heaviest rainfall (up to 2 inches, locally
up to 4 inches) 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.

//Leisure

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