FOUS30 KWBC 180834
QPFERD

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

Day 3  Valid 12Z Mon Jul 20 2026 - 12Z Tue Jul 21 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
ARIZONA AND NEW MEXICO...

...Southwest...
The primary adjustment for this forecast cycle is the introduction
of a Slight Risk across portions of New Mexico and Arizona. For
parts of the region, the setup remains much the same, with
anomalous moisture (2+ std dev above normal) supporting convective
activity and rainfall efficiency.

Mid-to-upper level energy/an inverted trough drifting east across
the region will provide larger-scale ascent to help better
organize monsoon convection. Furthermore, this feature will help
steer and push the convective and heavy rainfall threat a bit
farther west across portions of southeastern Arizona than in the
previous days. Given the combination of persistent anomalous
moisture, enhanced upper-level support, and sensitive soils,
expect localized rainfall rates to easily raise runoff concerns
across parts of the region. A surrounding broad Marginal Risk
remains in place extending up into the Great Basin and central
Rockies -- outlining the risk for less-organized storms, producing
isolated runoff concerns in those area.

...Upper Great Lakes...
A well-defined shortwave interacting with deepening moisture is
expected to produce strong storms capable of producing heavy
rainfall across the region. Guidance shows southwesterly to
easterly inflow supporting PWs increasing to around 2 inches. This
moisture along with strong ascent, afforded in part by favorable
upper jet dynamics, will fuel the potential for heavy rainfall-
producing storms. Training storms along the front may raise the
threat for heavy amounts and flash flooding concerns. Models differ
on the details, but there is some consensus for the heaviest
amounts centering from southern Wisconsin to northern Illinois,
where an upgrade to a Slight may be introduced in a future
issuance, if the trends hold.

...Eastern North Carolina...
A Marginal Risk was maintained where a front and coinciding pool of
deep moisture (PWs at or above 2 inches) are expected to linger,
extending the threat for heavy rainfall and possible flash flooding
into a second day.

...Florida Gulf Coast...
It remains uncertain how the disturbance in the eastern Gulf will
evolve and track. However, regardless of development, it is
expected that heavy rainfall will remain a threat for parts of the
Gulf Coast. Therefore, a Marginal Risk was maintained from the
Tampa Bay region to the Panhandle.

Pereira
 

Day 4 and Day 5  Valid 12Z Tue Jul 21 2026 - 12Z Thu Jul 23 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST AS WELL AS THE CENTRAL APPALACHIANS ON TUESDAY...

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN NORTH
CAROLINA AND SOUTHEASTERN VIRGINIA ON WEDNESDAY...

...Southwest...

The Southwest Monsoon will remain in full force across Arizona and
into Utah on Tuesday. Moisture anomalies especially to the north
across Utah could approach 5 sigma above normal for this time of
year, while into Arizona, PWATs to 2 inches will be a solid 3 sigma
above normal. With daytime heating, renewed rounds of thunderstorms
are expected to redevelop for the latest in the multi-afternoon
pattern. Soil moisture levels are already saturated over much of
Arizona and into southern Utah. Expect with the thermal low peaking
in intensity on Tuesday, that flash flooding concerns will become
more widespread as rains impact beyond the 4 Corners into Nevada,
Idaho, and Wyoming. A Slight Risk upgrade was introduced with this
update, and it's possible localized areas may see further upgrades
as Tuesday approaches. By Wednesday, ridging over the Southwest
will push the greater threats for thunderstorms further north into
the Intermountain West, with a low developing over the Plains
allowing for some of the moisture to overspread into portions of
the central Plains. The signal for heavy rain lessens on Wednesday,
so the threat drops to Marginal for now, though a Slight may be
needed into the Intermountain West with continued consistency in
the guidance.

...Central Appalachians...

A Slight Risk upgrade was also introduced for portions of the
Central Appalachians, particularly across West Virginia and into
southwest Pennsylvania. Abundant moisture across the Mid-Atlantic
will interact with a strong cold front pushing southwest across
Ohio during the afternoon. This will allow for numerous
thunderstorms to develop Tuesday afternoon. Upslope flow into the
flash flood prone mountains of West Virginia and Pennsylvania will
support additional thunderstorm development as compared with areas
further west where the front will clear the moisture, and further
east where there will be less forcing. PWATs approaching 2 inches
will also support storms capable of multiple inch per hour rainfall
rates, especially as they run into the mountains.

To the east across the Mid-Atlantic, moisture levels further
increase, with some areas perhaps reaching 2.25 inch PWATs Tuesday
afternoon. The forcing will be a bit more uncertain, but any storms
that form will be capable of very heavy rains. The I-95 corridor
from DC to NYC will have to be closely monitored as these heavily
populated and flood prone areas may have enough widespread activity
to need further upgrades.

...Tidewater of North Carolina and Virginia...

On Day 5/Wednesday, the same cold front that swings through the
Midwest, Northeast, and Mid-Atlantic on Tuesday slows down its
forward speed, perhaps even stalling to the west of the Tidewater
of North Carolina and Virginia. Plentiful tropical moisture
continues riding northeastward along that front, providing ample
opportunity for numerous training showers and thunderstorms to
develop over the region, likely moving out over the Atlantic off
Ocean City, Maryland and points north. Thus, the focus will be in
the highly urbanized Hampton Roads area, extending into much of the
coastal plain of North Carolina. Given the pretty impressive signal
for heavy rain, have started out the Day 5 ERO with a Slight Risk
in this region. There remains some uncertainty as to whether any
tropical development over the northeastern Gulf contributes to the
heavy rainfall expected in this region on Wednesday. Given the
signals for heavy rain expected Sunday/Monday over eastern North
Carolina, expect the soils by Wednesday to be significantly more
saturated than they are now, contributing to the heightened flash
flooding risk.

Wegman
$$
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