Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Fri Aug 7 2026
Day 2
Valid 12Z Sat Aug 08 2026 - 12Z Sun Aug 09 2026

...THERE IS A SLIGHT RISK ALONG THE SOUTHEAST COAST OF SOUTH
CAROLINA...

20Z Update..

In coordination with CHS, a Slight Risk was introduced for the
southeast coast of South Carolina. An inverted trough will move
northward from the east coast of FL, eventually reaching the SC
coast. Moisture from the Atlantic/Gulf Stream will push inland
beginning in the morning. 850mb flow will be nearly orthogonal to
the coast, and a persistent influx of moisture should aid in
sustaining showers and thunderstorms along the coast. HREF and RRFS
indicate medium-to-high chances (65% and 70% respectively) of rates
exceeding 1"/hr, and even medium (~45%) chances of 2"/hr during
the morning and early afternoon. SREF Spaghetti Plots also indicate
a large concentration of at least 1" along the coast. The biggest
limiting factor is expected to be the dryness of the soils.
Antecedent conditions suggest that soils will be able to handle a
lot of rain, however, persistent moisture flow, favorable rain
rates, and the urban centers of Charleston and Savannah being prone
to flash flooding, ultimately resulted in the addition of the
Slight Risk area.

Elsewhere, only minor adjustments were needed for the remaining
MRGL Risk areas. Global models were in a surprising amount of
disagreement over the Iowa and southern Minnesota, particularly
between the GFS and ECMWF regarding the QPF core. AI/ML guidance
(EC-AIFS & AIGFS) have honed in on an area in northern Iowa, almost
along the border. Totals also seem to be trending down with this
latest run. Given this and overall lack of a consensus among the
global suite, an upgrade was not considered. There is, however, an
agreement that northern Illinois no longer seems to be in the
picture for this setup, and as such, the MRGL Risk area was reduced
to remove that area.

Blanco-Alcala

Previous Discussion...

Monsoonal moisture across the Southwest will continue on Saturday,
especially across Arizona. As usual, the greatest rainfall will be
along the Mexican border where the Gulf of California's influence
is greatest, as well as along the Mogollon Rim. There appears to be
little rain in between in the populated areas. Lack of signal for
more organized heavy rain should preclude a Slight Risk upgrade.

Across the Midwest, specifically Iowa, an overnight Saturday night
MCS is expected to impact much of Iowa and small portions of the
neighboring states. While guidance has come into better agreement
on the areas likely to be affected, there remains a broad variety
of solutions as to how much rain will fall across much of central
and eastern Iowa. Thus, for now the area remains in a Marginal, but
will continue to be monitored for a Slight risk upgrade with future
updates.

Signals for heavy rain across much of the Eastern Seaboard remain
very diffuse again on Saturday. Similar to Friday, there remains
plentiful moisture all up and down the Atlantic coast. Somewhat
better forcing from a negatively tilted trough north of the Great
Lakes should allow for more widespread storms, but they will remain
quite progressive. Further south, there will be more moisture, but
a lack of forcing. Most of the heaviest rains look to be from north
Florida through coastal South Carolina.

Wegman


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