Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Mon Jul 20 2026
Day 2
Valid 12Z Tue Jul 21 2026 - 12Z Wed Jul 22 2026

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHWEST AND THE MID-ATLANTIC TO THE OHIO VALLEY...

...Intermountain West...

Monsoonal moisture continues to arrive over the Southwest from the
sub-tropical Pacific around a mid-level high centered over
Colorado. A shortwave trough will track from southwest NM into
eastern AZ which will promote increased convective coverage over
both AZ and UT into NV. The Slight Risk area was further expanded
to include most of UT through central NV. The greatest convective
coverage and most impactful flash flooding is still expected from
southeast AZ up through the Mogollon Rim to the Grand Canyon which
is considered a more "enhanced" Slight Risk. A fair amount of
convective coverage tonight over AZ may cause some opaque stratus
to persist into Tuesday which could at least locally disrupt the
diurnal trend in activity.

The PW anomaly reaches 4 standard deviations above normal over the
Sierra Nevada on Tuesday. This should promote vigorous diurnal
convection up the High Sierra to Lake Tahoe. A Slight Risk may be
warranted, but for now an expanded Marginal Risk is drawn.

...Mid-South through the Ohio Valley and Mid-Atlantic into New
England...

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
Ohio Valley and Interior Northeast through the Mid-Atlantic on
Tuesday, likely holding together for the into New England Tuesday
evening. PW of 2 to 2.25" ahead of the front and sufficient
instability will allow for heavy rainfall through this area,
possibly as far west as the Mid-South (per the RRFS and the 12Z
HRRR) and as far east as the New England coast up through Down East
Maine. Mean layer Wly to SWly flow of 40-50kt will keep activity
moving, but the threat for backbuilding and training storms as well
as the book ends of any segments could cause widely scattered
instances of flash flooding. The Slight Risk was expanded per 12Z
(and 18Z HRRR) CAM consensus along with chats with WFO PHI/OKX
through the northern Mid-Atlantic into Connecticut.

...Gulf Coast...

Tropical Depression 2 is still forecast to gradually drift west
with the center offshore until reaching southern Louisiana early
Thursday. Northerly shear and dry air entrainment will continue to
focus most associated precip south of the center with the banding
seen today east and north of the track over FL diminishing tonight
and having less coverage for Tuesday. This is in spite of this
being a tropical cyclone with PWATs up to 2.5 inches. Therefore,
the Marginal Risk for the Florida Panhandle through southeast
Louisiana remains in place with few changes.

Jackson/Wegman


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