FOUS30 KWBC 190921
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
521 AM EDT Sun Jul 19 2026

Day 3  Valid 12Z Tue Jul 21 2026 - 12Z Wed Jul 22 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST, CENTRAL APPALACHIANS, OHIO VALLEY, AND THE MID ATLANTIC COAST...

...Southwest to the northern Rockies...
Models show the upper high continuing to shift east as an upper
trough begins to drift into the Pacific Northwest. This will allow
the monsoon moisture plume to spread further north, with moisture
anomalies over 3 std dev above normal extending as far north as the
northern Rockies. This will support increasing convective
development with isolated flash flooding concerns as far north as
southwestern Montana and southern Idaho.

However, the greater heavy rainfall and flash flooding threat is
expected to remain centered over western New Mexico, Arizona, and
southern Utah. Guidance shows a fairly well-defined shortwave
moving around the western periphery of the upper high, which along
with PWs over 1.5 inches in many spots, and highly sensitive soils,
will likely generate additional widespread storm coverage and flash
flooding concerns. Given the synoptic setup and anomalous
moisture, this can be considered a high-end Slight for parts of the
region and a future upgrade may be required.

...Central Appalachians and Ohio Valley...
A Slight Risk remains in place across portions of the central
Appalachians and Ohio Valley. Moist soils and flood-prone mountain
terrain are likely to contribute to the flash flood threat across
this region. Deep moisture (PWs around 2 inches) will fuel showers
and storms ahead of a strong cold front advancing southeast across
the region. These storms will be capable of producing 1-2 in/hr
rainfall rates, raising flash flooding concerns.

...Mid Atlantic...
A separate Slight Risk has been introduced along the Mid Atlantic
Coast for late Tuesday into early Wednesday. Strengthening
southeasterly flow ahead of the system moving through the Ohio
Valley will transport a deeply anomalous moisture plume into a
region of strong ascent. This combination will support increasing
coverage of showers and storms capable of producing heavy rainfall.
While the exact spatial coverage of heaviest amounts remains
somewhat uncertain, portions of the the more flood-prone urbanized
I-95 corridor appear to likely be impacted, warranting the upgrade
to a Slight Risk.

...Gulf Coast...
With the heavy rainfall footprint associated the Gulf disturbance,
remaining offshore in most of the guidance, continued to maintain
only a Marginal Risk along parts of the immediate Gulf Coast.

Pereira
 

Day 4 and Day 5  Valid 12Z Wed Jul 22 2026 - 12Z Fri Jul 24 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE COASTAL
CAROLINAS AND SOUTHEAST VIRGINIA ON BOTH WEDNESDAY AND THURSDAY...

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
INTERMOUNTAIN WEST ON WEDNESDAY...

...Tidewater Region of Virginia and the Carolinas...

A slow-moving cold front pushing southeast out of the Mid-Atlantic
on Wednesday is likely to continue slowing down its forward speed
as it approaches the Tidewater Region of Virginia and the Carolinas
on Wednesday. Meanwhile, plentiful tropical moisture will be drawn
northeastward from the tropical system that will likely be
meandering somewhere near the Louisiana coast on Wednesday. This
moisture will ride northeastward ahead of the front, spiking PWATs
above 2.25 inches over this entire region. The result of a strong
but slow-moving front, well above normal amounts of moisture, and
upper level support in the form of a deep trough over the Northeast
supporting the surface front from behind/north will make for a
nearly ideal scenario for training and backbuilding storms from the
afternoon through the evening.

This Day 4/Wednesday period is likely to be the fourth consecutive
day that showers and thunderstorms have been dropping locally very
heavy rain and multiple-inch rainfall totals somewhere in and
around eastern North Carolina. The front will act to greatly expand
the footprint of heavy rainfall in this area. Since soils are all
but certain to be nearly saturated in this area by Wednesday, flash
flooding concerns continue to increase. Thus, a higher-end Slight
was introduced with this update from Raleigh east, and from
Wilmington north through the Hampton Roads area. It's probable that
should the trends continue to increase both with the expected
rainfall on Wednesday, and the prior days' rainfall in this same
region, that a Moderate Risk upgrade will be needed with future updates.

By Day 5/Thursday, the front will sag a hair bit further south,
likely sparing the Raleigh and Hampton Roads metros from much
additional rainfall, but instead concentrating the heaviest rains
from the Outer Banks southwest down the coast through Wilmington
and including Charleston, SC in heavy rainfall. The ERO thus was
started this morning with a Slight Risk for this area. Of course,
even just a small increase in forward speed will push the front up
to the coast, which would then concentrate all of the heaviest
rains off the coast, making the Slight Risk an over-forecast.
However, any slower/westward positioning of the front will make
for a 5th consecutive day of heavy rains in eastern North
Carolina...meaning the Slight Risk would be an under-forecast.
Thus, the Slight represents the "happy medium" of these scenarios
and fits best with the current rainfall forecast in the area for Thursday.

...Intermountain West...

A Slight Risk upgrade was introduced with this update for a portion
of the Intermountain West on Wednesday. The area highlighted
includes all of southeastern Idaho, much of western Wyoming outside
of Yellowstone, as well as far northern Utah and the northwestern
corner of Colorado. Well above normal amounts of atmospheric
moisture to the tune of up to 4 sigma above normal, and PWATs
locally exceeding 1.25 inches will be in place across this region.
An approaching longwave trough will direct a strong shortwave
northeastward during the afternoon hours. This will result in
widespread shower and thunderstorm activity over this area.
Topographic interaction with the storms will locally enhance
rainfall rates, while also supporting impactful flash flooding as
the rain water races down the slopes of the mountains. Due to the
abundant moisture available, the storms will not only be numerous,
but capable of 2 inch/hour rainfall rates with the strongest cores,
a phenomenon not often seen in this part of the country.

Wegman
$$
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