FOUS30 KWBC 200827
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Mon Jul 20 2026

Day 1  Valid 12Z Mon Jul 20 2026 - 12Z Tue Jul 21 2026

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST AS WELL AS FOR EASTERN NORTH CAROLINA...

...Southwest...

Very few changes were needed with the inherited Slight Risk area
from far west Texas, southwestern New Mexico, and much of Arizona
with this update. Monsoonal moisture will stream north off the Gulf
of California and into the Four Corners region today. With peak
heating, afternoon thunderstorms are expected over much of the
Slight Risk area. Much of the area has seen afternoon thunderstorms
causing localized flash flooding in recent days, and the same
pattern continues today. The threat further east will be driven by
a subtle shortwave disturbance retrograding west along the Mexican
border. This will allow for greater longitudinal spread of storms
to include far west Texas. MUCAPE values will be between 1,000 and
2,000 J/kg across much of the region, as PWATs rise above 1.5
inches in some areas. Between the aforementioned disturbance and
local topography, expect widely scattered instances of flash
flooding where the storms today are most persistent.

...Eastern North Carolina...

A stalled out front along the VA/NC border at the start of the day
will retreat northward in the form of a warm front as deep tropical
moisture advects northeastward from the tropical depression in the
Gulf. The front will provide enough forcing across much of eastern
North Carolina to allow for a renewed round of widespread showers
and thunderstorms in the area. Soils remain generally dry over most
of the area, despite storms impacting some of eastern North
Carolina yesterday. Due to the well above normal amounts of
moisture for the storms to work with, as well as the front
providing some forcing, the Slight Risk was expanded west to
overlap some of the areas of North Carolina that are being impacted
by storms currently, generally just east of Charlotte. Otherwise,
the threat remains similar to yesterday, so few changes were needed
with this update.

...Gulf Coast...

The outermost northern and western periphery of Tropical Depression
Two continues to impact much of the Gulf Coast of Florida, through
the Panhandle, and over to southeastern Louisiana. The storms are
few and far between, but ample moisture associated with a
developing tropical cyclone is allowing for any storms to have the
potential to produce multiple inch per hour rates. Regardless, the
center remains far enough offshore, with drier air aloft working to
significantly cut down on the overall coverage of storms.
Considering the dry soils and high FFGs typical of the immediate
Gulf Coast, even periods of heavy rain should only result in
isolated instances of flash flooding. Thus, the inherited Marginal
remains in place.

...Midwest...

The Marginal Risk across much of the Midwest and upper Great Lakes
also remains largely the same today. There remains considerable
uncertainty as to coverage of storms impacting the area today into
tonight. It appears the most likely areas to be impacted stretches
from the southeastern corner of Minnesota south through eastern
Iowa and into northeastern Missouri. However, even in this area,
dry soils and the height of the growing season should allow most of
the rain expected to water the crops in the region, with minimal
threat for flash flooding. Thus, few changes were needed with this update.

Wegman
 

Day 2  Valid 12Z Tue Jul 21 2026 - 12Z Wed Jul 22 2026

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
ARIZONA AND UTAH, AS WELL AS THE UPPER OHIO VALLEY AND INTO THE
MID-ATLANTIC...

...Arizona into Utah...

Increasing monsoonal moisture, particularly into southern Arizona
will combine with an approaching upper level shortwave trough to
further increase convective converage across portions of the
Southwest on Tuesday as compared with previous days. The
introduction of a northwestward-moving shortwave trough will allow
the convective activity to wane over eastern New Mexico and west
Texas, and instead promote more activity into eastern Nevada, Utah,
and portions of Colorado and Wyoming. Numerous highly flash-flood
prone slot canyons, dry washes, and rocky soils will allow the many
storms that form over the region to cause scattered instances of
flash flooding. The Slight Risk area was expanded north to include
much of Utah and into eastern Nevada for this region. The greatest
convective coverage and most impactful flash flooding is expected
over portions of Arizona and the boot heel of New Mexico. A
higher-end Slight remains in effect along the Mogollon Rim, but has
been expanded to the Mexico border along the AZ/NM border with this update.

...Upper Ohio Valley through the Mid-Atlantic...

A strong cold front pushing south across the Midwest will run into
plentiful tropical moisture being drawn north from Tropical
Depression 2 in the Gulf. The front will act as a catalyst for
numerous segments of mostly fast moving thunderstorms across the
Mid-Atlantic and Ohio Valley on Tuesday. With PWATs ahead of the
front over 2.25 inches in some instances, and in most areas above 2
inches, the storms will have plentiful juice to work with, allowing
for heavy rainfall to impact most areas from the central and
northern Appalachians to the urban I-95 corridor from Richmond up
through Boston. The fast moving nature of the storms should mean
most areas have severe concerns as higher priority than flash
flooding. However, it's likely that backbuilding and training
storms on the book ends of any segments could cause widely
scattered instances of flash flooding. Thus, the Slight Risk
inherited over much of the Mid-Atlantic remains in place with few changes.

...Gulf Coast...

Tropical Depression 2 is expected to gradually drift west, with the
center following near the Gulf Coast. All of the guidance suggests
that northerly shear and dry air entrainment will push any
meaningful associated heavy rainfall south of the center over the
Gulf, leaving very little rainfall to impact the immediate Gulf
Coast. Thus, despite being a tropical cyclone with local PWATs up
to 2.5 inches, the distinctive lack of rainfall for most land
areas, especially away from the immediate coast remains an unusual
feature with TD2. The Marginal Risk in place over most of the
northern Gulf Coast from the Florida Panhandle west through
southeast Louisiana remains in place with few changes.

Wegman
$$
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