Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
835 PM EDT Thu Aug 20 2026
Day 2
Valid 12Z Fri Aug 21 2026 - 12Z Sat Aug 22 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
VIRGINIA AND THE CAROLINAS...

20Z Update...

Changes to the previous Day 2 ERO includes expanding the SLGT Risk
in the Carolinas and Virginia westward to include parts of the
southern/central Appalachians, including northwest NC and Southwest
VA. Additionally, a MRGL Risk was added for parts of central NE and
north-central KS.

For the southern Mid-Atlantic, the meteorology remains consistant
to previous discussions. 12Z CAMs and REFS/HREF guidance show solid
coverage over 2-4" amounts across central NC into adjacent north-
central SC, with localized maximum amounts up to 7". HREF/REFS
neighborhood probabilities for >5" are now 30-60%. This includes
the Sandhills of the Carolinas where FFGs are higher, but also
extends into the Piedmont where terrain is more at risk for flash
flooding. Given the expansive QPF westward, the SLGT risk was also
expanded. A MDT risk was considered, but given some uncertainty in
placement of heaviest QPF and still limited areal coverage of 5"+
probabilities, a SLGT was maintained.

For parts of the Central Plains, northwest flow around an upper-
level ridge centered over the Southern Rockies will allow for a
diving weak shortwave to interact with a frontal boundary to
produce locally heavy rainfall. Guidance remains isolated with this
risk, but the setup and PWs creeping up to 1.5" support the
potential for overrunning showers/storms during the evening and
overnight across parts of central NE into north-central KS.
HREF/REFS neighborhood probabilities are not too impressive for at
least 2", but do reach up to 30% as of the 12Z runs.

Snell

...Virginia to Carolinas...

Cold front will slowly advance south into the Carolinas during the
end of the D1 into D2 time frame with an eventual transition to a
quasi-stationary front as it reaches the latitude of north GA into
the Piedmont of SC. Moisture pooling along the front with continued
forcing driven by another shortwave advancing through the
Tennessee Valley will lead to another round of heavy convection in-
of the Southern Mid Atlantic with the primary axis likely to occur
from the southern Delmarva through the VA Tidewater into the
Carolina's. Environment across the region outlined will remain very
buoyant with PWATs between 2-2.3" for the entire area along and
south of the front. Models are consistent with their signature of
1-2" of rainfall on an areal average basis with some of the
deterministic outputs approaching upwards of 3-5" where storm
materialize and settle as the steering pattern weakens as we step
into the D2. Rainfall rates between 2-3"/hr with intra-hour rates
upwards of 4"/hr are forecast across the aforementioned area,
plenty aggressive enough to cause at least scattered flash flood
prospects, especially in more urbanized zones along I-95 and points
east. The most notable locations in the guidance are over the
Columbia, SC area up through Florence into east-central NC. 00z
HREF neighborhood probabilities for >3" within the 12z Fri to 00z
Sat period are running between 50-90% with the above zone with the
maxima focused between I-74/95 just southwest of Raleigh.
Instability across the area will be fairly robust with 1000-2000
J/kg of MLCAPE on average across NC with upwards of 2500-3500 J/kg
located down into SC. Deep, moist atmospheric profiles are
prevalent with the latest CAMs suite, as well relaying a textbook
heavy convective signature across much of the Carolina's,
especially along and east of the Piedmont.

With the signal maintaining consistent in the heavy QPF placement
and with a favorable environment for locally enhanced rainfall, the
SLGT risk was maintained from the previous forecast with an
addition of high-end SLGT wording as the threat for locally
significant rainfall >4" has increased steadily since the last few
updates.

...Southwest...

Monsoonal activity will continue for another day as the Southwest
CONUS lies underneath a broad ridge centered over the Four Corners
with multiple mid-level vorticity maxima pivoting under the ridge
axis. Seasonal to slightly elevated PWATs will extend throughout
the Southwest, even reaching a bit further north into the Great
Basin by Friday leading to some locally heavy rainfall even making
its presence into portions of NV and central UT while also
impacting those same areas that saw activity the prior period.
Local totals of 1-2" are forecast, but areal QPF average is pretty
much between 0.25-0.5" which is typical for these types of setups.
A broad MRGL remains in effect for much of the Desert Southwest up
into the Great Basin, extending east into the Southern Rockies
located over southwestern CO into NM.

Kleebauer


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