Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Fri Aug 7 2026
Day 1
Valid 16Z Fri Aug 07 2026 - 12Z Sat Aug 08 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
NORTHEAST AND THE NORTHERN MID-ATLANTIC...

16Z Update..

A Slight Risk was introduced in this update for eastern
Pennsylvania, southeast New York, and northern New Jersey. A pulse
of upper-level forcing by way of a shortwave will quickly move
through the northern Mid-Atlantic in the afternoon hours.
Anomalously high moisture availability, with PWATs exceeding 2", is
also expected. A line of short- lived thunderstorms will bring
heavy rainfall, in the afternoon and early evening, with hourly
rain rates potentially reaching and/or exceeding 2"/hr. Previous rainfall
over the past few days have also lowered FFGs, to where areas in
eastern PA, southern NY, and northern NJ only need around 0.5-0.75"
per hour to exceed them. Latest HREF and RRFS runs also support
the potential, with medium-to-high chances (~65%) in the FFGs
exceedance probabilities in both models. As such, and in
coordination with the OKX, LWK, PHI, and BGM, a Slight Risk was
introduced. Additionally, MPD #962 in association with this event
has been issued through 21Z.

Elsewhere, no further changes were needed in terms of the MRGL Risk
throughout much of the country. Thought was given toward an upgrade
in northern AR, where an influx of moisture intersecting with the
Ozarks could result in heavier rain throughout the afternoon.
Ultimately, an upgrade was not needed mostly due to the very high
FFGs, which rainfall will struggle to meet. Isolated flash flooding
will remain a concern, however.

Ongoing convection in Minnesota is set to continue over the next
several hours, and has already brought spots of 1"/hr rates.
7-8/C/km lapse rates, solid instability (~2000J/kg), and PWATs
around 1.5" will continue to support heavy rainfall. Storm motion
will be quite progressive, however, and 1hr FFGs remain above 1.5".
Given that, keeping a MRGL area was sufficient. Isolated instances
of flash flooding remain possible however, and as such, MPD #963
has been issued through 2130Z.

Blanco-Alcala

Previous Discussion...

Marginal Risks for excessive rainfall cover large portions of the
country from the Southwest through much of the eastern half of the
country. The Marginal was expanded to include much of Oklahoma and
north Texas, as well as expanded through Louisiana and portions of
the central Gulf Coast, as well as much of Florida.

Abundant deep tropical moisture is in place across much of the
Southeast and up the Eastern Seaboard. Forcings remain mesoscale,
as the synoptic pattern with a trough generally along the northern
tier of states generally is not overlapping most of the deepest
moisture. Thus, where there is enough forcing, there's a lack of
moisture, and in large swaths of the country where there's plenty
of moisture, a lack of a defining synoptic feature to provide
forcing will likely mean any storms will be reliant on smaller
mesoscale features such as local terrain, cold pools, sea breezes
etc. to get them going.

Due to a lack of defining features overall, large Marginals remain
the most prudent forecast. However, given the aforementioned deep
tropical moisture over much of the country, it's quite feasible
that there will be Slight Risk levels of impacts wherever the
storms can interact with each other in a positive way. This appears
most likely on Friday across portions of Arkansas, where the deep
tropical moisture will run into the terrain of the Ozarks, and the
base of the distant upper level trough could provide a bit of
organization to the convection. That said, the very dry soils from
the lack of rainfall across the state in recent days will make
Slight level impacts difficult to attain.

From eastern Ohio through much of Pennsylvania and southern New
York, there too will have some minimal amount of forcing from weak
upper level shortwaves running over the abundant summertime
moisture in place across much of the east. Here too there is a
higher risk of Slight Risk level impacts, in part due to low FFGs.
Convection across this region looks to be quite progressive though,
so it will likely take topographic enhancement in localized areas
to produce enough rain to produce widely scattered instances of
flash flooding. These should be few and far between enough to not
need a Slight there for now.

Wegman


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