Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
620 PM EDT Tue Jul 21 2026
Day 2
Valid 12Z Wed Jul 22 2026 - 12Z Thu Jul 23 2026

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL OVER PORTIONS
THE TIDEWATER OF VIRGINIA AND NORTH CAROLINA...

...Carolinas, Southern Virginia, and Northern Georgia...

21Z update... Given the steady influx of tropical moisture from
T.S. Bertha northeastward into the sinking strong cold front,
widespread convection with embedded heavy rainfall will focus over
North Carolina and Virginia Tidewater region. There is a signal for
2 to 4 inches for this part of the country and rainfall rates could
easily exceed 1.5/2 inches per hour. Training/repeating of storms
expected along the frontal boundary therefore a Moderate Risk was
raised for this period.

Campbell

A strong cold front running into highly anomalous moisture being
siphoned from the circulation of Tropical Storm Bertha will
exacerbate the gradient of moisture along the frontal interface
through the day across the Carolinas and into southeastern
Virginia. This will work to keep any forward progress of the front
minimal. Storms will train along the front, especially across
northeastern North Carolina and into southeastern Virginia. This
area remains in a higher-end Slight Risk and with the stalled out
front remaining to guide the frequent development of additional
storms, a Moderate Risk upgrade in areas where the storms focused
in the Day 1 period remains a distinct possibility. Guidance has
been laser focused in this area and so forecast changes have been
minimal. Further south and west, however, guidance has become
increasingly optimistic on storms developing further west into the
southern Appalachians. As such, the Slight Risk was expanded west
to include this region from north of Atlanta through the western
Carolinas.

...Intermountain West...

21z update... Minor expansions of the Marginal Risk were made
across north-central Arizona and eastern Kansas to reflect the new
WPC QPF placement. The latest CAMs indicated a modest uptick in
convection for north-central and southeast Wyoming and northeast of
Boulder Colorado, which was just outside the inherited Slight Risk
area. Therefore eastward adjustments were made to the Slight Risk
area.

Campbell

Highly anomalous amounts of atmospheric moisture associated with
the monsoon over the Intermountain West will be activated by rapid
height falls as an upper level and highly negatively tilted trough
pushes east from off the coast of Washington and Oregon. Meanwhile,
separate upper level energy undercutting the ridge will also
provide additional forcing further east across eastern Idaho and
Wyoming. Once again, numerous thunderstorms will form in the
anomalous moisture and for many areas, will be tied to the local
topography. Few changes were needed with this update. The greatest
amounts of rain look to concentrate in western Wyoming, where any
storms south of Yellowstone could necessitate a higher-end Slight
for some of those areas, as well as for the Uintas of northern
Utah. With nearly all of the forcing further north, the Marginal
Risk into southern Arizona and southern New Mexico was trimmed
significantly with this update, as ridging quickly overtakes this
area and limits convective potential south/west of the Mogollon Rim
as a result.

...Tropical Storm Bertha/Gulf Coast...

Strengthening shear across the circulation will continue to keep
any organized convection and meaningful rainfall out over the open
waters of the Gulf. The immediate coastline could still see amounts
greater than an inch, but the rainfall footprint continues to shift
off the coast. In coordination with LIX/Slidell, LA forecast
office, the inherited Slight Risk for this region was downgraded
with this update, with the overall area of the surrounding Marginal
remaining little changed. What little rainfall does impact land
areas remains with the potential to be locally heavy, so
unfortunately no changes to the Marginal Risks can be made so long
as Bertha remains a tropical entity.

Wegman


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt