Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
729 PM EDT Thu Aug 27 2026
Day 1
Valid 01Z Fri Aug 28 2026 - 12Z Fri Aug 28 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
GULF COAST AND THE NORTHEAST/MID-ATLANTIC...

...Northeast/Mid-Atlantic...
The Slight Risk area was adjusted for recent radar reflectivity
trends and 18z HREF/12z RRFS guidance. Portions of NJ were
stabilized by convection earlier today, and the guidance suggests
that heavy rain concerns could continue as late as 06z in/near an
area of 1.5-1.75" precipitable water values, effective bulk shear
of 25-30 kts, and ML CAPE of ~2000 J/kg. Hourly rain amounts have
peaked at 2.5" at times per radar estimates. Local totals near 5"
remain possible until convection wanes.


...Southeast and Gulf Coast...
The tail-end of the longwave upper trough, with distinct shortwave
energy traversing the Gulf Coast, along with the stationary front,
will provide the dynamical focus for more organized (widespread)
areas of convection across this region through 04z or so before
waning for several hours overnight, and then picking up during the
early morning hours on Friday. Flood prone urban areas such as New
Orleans, Mobile, and some of the more interior areas of
Mississippi dealing with the latest of multiple days of heavy rains
could experience widely scattered instances of flash flooding.


...Southwest...
Convection across the Southwest should fade by roughly 04z, while
activity across the High Plains lingers into early Friday morning
as current thunderstorms across NE drop southward with time. In the
High Plains, ML CAPE is 1500-3000 J/kg presently and effective bulk
shear of 30-40 kts should allow for convective organization,
including mesocyclone formation. Coverage is not expected to be
broad, so the Marginal Risk category continues to suffice. Hourly
rain amounts to 2" are possible where storms merge, congeal,
mesocyclones form, or thunderstorms show some training character.

Roth


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt