Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Sat Sep 02 2023

Valid 00Z Sun Sep 03 2023 - 00Z Tue Sep 05 2023

...Risk for scattered flash flooding in the Intermountain West as
unsettled and cool weather pattern continues...

...Many record-tying/breaking temperatures possible as hot weather remains
in place over the Northern Plains/Upper Midwest...

...Unseasonably hot temperatures for the Mid-Atlantic to end the Holiday
Weekend...

An unsettled and cool pattern will remain over much of the West this
weekend as an upper-level low has stalled out overhead. Waves of
upper-level energy rotating around the low and a lingering frontal
boundary will help to trigger widespread showers and thunderstorms, with a
focus on the Intermountain West. Plentiful, anomalously high surface
moisture will be in place to contribute to numerous heavy rain producing
storms both due to the coverage/duration and intensity of the downpours.
There is a Slight Risk of Excessive Rainfall in place for portions of the
northern Great Basin/Northern Rockies Sunday where the best combination of
upper-level energy and moisture/instability will lead to the highest
chance for some scattered instances of flash flooding. The upper-level
wave will begin to move eastward on Monday, with the threat for heavy
rainfall shifting into the Northern Rockies/adjacent High Plains. An
additional Slight Risk of Excessive Rainfall is in place with a continued
risk for some scattered flash flooding. High temperatures will remain
unseasonably cool for early September across most of the West. Forecast
highs both Sunday and Monday will range in the 60s and 70s for much of the
Pacific Northwest, western Great Basin, and California, with only the
Desert Southwest seeing hotter temperatures into the 90s and low 100s.
These cooler temperatures will also spread into the Northern
Rockies/adjacent High Plains and eastern Great Basin Monday.

Meanwhile, to the east, a broad upper-level ridge will keep temperatures
unseasonably hot for much of the central/eastern U.S. It what has already
been a long, hot Summer, highs will remain in the upper 90s to low 100s
for Texas and the Southern Plains, as well as portions of the Central
Plains.   
However, much of the focus will be on the Northern Plains and Upper
Midwest where highs into the low 100s are upwards of 20-30 degrees above
average and will be at record-tying/breaking levels. Some monthly records
are even possible. The unusual nature of heat of this magnitude this time
of year will heighten the related health risks, especially over a holiday
weekend. The upper-level wave over the West will continue eastward into
Tuesday helping to drive a pair of frontal systems into the region,
bringing a chance for showers and storms and eventual relief from the heat
just beyond the current forecast period into Wednesday. The unseasonably
hot weather will also overspread the Northeast by Sunday. Highs will range
in the mid- to upper 80s Sunday before reaching as high as the low 90s on
Monday. Some record-tying/breaking temperatures will be possible in the
Mid-Atlantic as highs soar into the mid-90s. Elsewhere, a weak upper-level
wave and lingering frontal boundary will bring a chance of some
thunderstorms to the Lower Mississippi Valley. Highs across the Lower
Mississippi Valley and into the Southeast and Florida will also be more
seasonable compared to the rest of the central/eastern U.S., with mid-80s
and upper 90s expected for Sunday and Monday.

Putnam

Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php