FOUS30 KWBC 180834
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Sat Jul 18 2026

Day 1  Valid 12Z Sat Jul 18 2026 - 12Z Sun Jul 19 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHWEST, GREAT BASIN, WEST TEXAS, AND THE NORTHEAST...

...Western Texas to the Four Corners/Great Basin...
Overall, the forecast remains much the same, with mostly minor
spatial adjustments required based on the latest hi-res ensemble guidance.

One of the bigger adjustments was a northward extension
of the Slight Risk across western Texas into the southern
Panhandle. This northern expansion was supported by a slow-moving
upper level shear axis combined with low-level southerly flow,
fueling notable moisture advection into that region. Both the HREF
and REFS guidance have trended more bullish, showing localized
potential for rainfall amounts exceeding 3 inches. These totals
will be capable of producing rapid runoff and localized flash
flooding, especially where soil conditions are more sensitive from
recent rainfall.

Farther west, the Slight Risk remains largely unchanged across
portions of New Mexico, Arizona, southern Utah, and southwestern
Colorado. This remains supported by high-moisture anomalies and
indication from the HREF and REFS for rainfall rates likely to
reach at least 0.5 in/hr in the stronger cells. The Mogollon Rim
looks to remain a focus storm initiation and for some of the higher
storm totals, with both the HREF and REFS showing high
probabilities for accumulations over 2 inches in that area. Recent
heavy rains across this area will likely make it more susceptible
to additional flash flooding.

...Midwest to the Mid Atlantic and Northeast...
A progressive cold front dropping southeastward is expected to
interact with an anomalously moist airmass pooling ahead it. While
the primary Slight Risk remains focused across parts of the
northern Mid Atlantic to southern New England, the broad western
shield of the Marginal Risk was expanded farther west across the
Ohio Valley and into northern Illinois. Within this area, a smaller
Slight Risk area was added over portions western Pennsylvania
where the latest HREF and REFS are indicating localized amounts of
2-3 inches are likely.

For the Slight Risk area over the northern Mid Atlantic and
Northeast, guidance shows two rounds of storms impacting portions
of eastern Pennsylvania, New Jersey eastward to southern New
England. A leading round of storms, well in advance of the front,
is expected to impact the region this afternoon, followed by a second
round accompanying the front itself during the overnight. Many of
the hi-res members suggest the heavier rainfall and potential flash
flooding threat will accompany the initial round, with the loss of
daytime heating and more stable air limiting the threat with the
second. With at least the first round, highly-efficient warm rain
processes and localized cell training may yield quick, short-
duration totals capable of producing isolated to scattered runoff
concerns, particularly in low-lying or urbanized areas. The Slight
Risk largely reflects the higher HREF probabilities for
accumulations of 3 inches or more.

...Florida Panhandle into Southeast Alabama and Southwest Georgia...
Deep moisture spreading north ahead of a slow-moving mid-to-upper
level low will pool along a surface trough extending out of the
eastern Gulf. This moisture (PWs increasing to around 2 inches)
will fuel slow-moving storms developing by the late afternoon that
will be capable of producing heavy rates, which along with their
slow movement, may produce heavy amounts and isolated flash
flooding.

Pereira
 

Day 2  Valid 12Z Sun Jul 19 2026 - 12Z Mon Jul 20 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS THE
SOUTHWESTERN U.S. FROM WEST TEXAS TO SOUTHERN UTAH...

...Southwestern U.S....
The overall synoptic configuration remains largely unchanged from
the previous period, with a persistent monsoon pattern locked in
place -- keeping scattered to widespread convection in the forecast
from West Texas into the Great Basin and southern Rockies. Given
that PW anomalies remain notably high at 2-3 std dev above normal,
and soil conditions moist from prior rainfall, confidence was
sufficient to introduce a Slight Risk that extends from West Texas
northeastward across southern New Mexico, central and northern
Arizona, into southern Utah.

An upper-level high centered over northern Utah and Colorado will
support steady easterly flow across the southern tier, effectively
tapping into and beginning to pull mid-level energy that has been
centered over West Texas along this deeper moisture axis. The
highest areal average precipitation amounts are expected to center
along the higher terrain, where slow-moving storms are expected to
develop with afternoon heating, before propagating off of the
terrain along convective outflows. Given sensitive, moist soil
conditions from successive days of widespread storms, much of this
area remains vulnerable to rapid runoff. Complex terrain, slot
canyons, and recent wildfire burn scars will further accentuate the
threat for flash flooding across parts of the region.

...Mid Mississippi Valley east to the Carolinas and south to the
Eastern Gulf Coast...
A more expansive Marginal Risk has been drawn for this period,
reflecting deep moisture atmospheric profiles and an increasing
potential for localized heavy rainfall amounts producing isolated
runoff concerns. This risk is centered along a cold front dropping
into North Carolina and the Tennessee Valley, while is begins to
slow over the lower Ohio and mid Mississippi valleys. Diurnal
heating and prefrontal convergence will tap into this moisture
pool, generating clusters of slow-moving efficient thunderstorms,
capable of producing 1-2 inch totals, with isolated higher amounts.
There remains a greater threat for more widespread heavier amounts
along the eastern extent of this area, centered over southeastern
Virginia and eastern North Carolina, where more defined upper
forcing will help accentuate the threat for amounts over 3 inches.

Additionally, the Marginal Risk has been extended southward down to
the Gulf Coast. This accounts for the deep tropical moisture
arriving ahead of the slow-moving disturbance lingering in the
eastern Gulf, as well as favorable low-level convergence focusing
along a slow-moving surface trough extending north from the Gulf.
Highly efficient warm-rain processes along these features will
maintain a threat for heavy, short-term duration totals and
isolated runoff concerns.

Pereira
$$
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