Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
407 PM EDT Thu Sep 01 2022

Valid 00Z Fri Sep 02 2022 - 00Z Sun Sep 04 2022

...Prolonged and potentially dangerous heat wave continues to expand
across much of the West...

...Widespread showers and thunderstorms, including a Slight Risk for flash
flooding, forecast from Texas into the Lower Mississippi Valley...

...Cold front to bring fall-like temperatures to the Upper Midwest and
Great Lakes...

A prolonged and possibly record heat wave building over the Western U.S.
is the main headline as we head into the upcoming holiday weekend (and
lasting well into the medium range period as well). Starting in the
interior Pacific Northwest,  high temperatures in the low to mid-100s are
forecast on Friday before the passage of a cold front brings some relief
for Saturday. Temperatures will soar into the upper 90s to low 100s for
the Northern Rockies and Northern High Plains of Montana on Saturday.
These temperatures are upwards of 25 degrees above normal for early
September. For the Great Basin, highs will be in the upper 90s to low 100s
both Friday and Saturday. The Desert Southwest as well as the Sacramento
and San Joaquin valleys of California will see highs in the mid-100s to
low 110s, while highs for interior portions of coastal California will be
in the upper 90s and low 100s. Numerous record-tying/breaking highs are
possible across the entire region and widespread heat-related advisories
are in place. The heatwave will pose a high to very high risk to the
general population, particularly the elderly and those without adequate
air conditioning, due to both the intensity of the high temperatures and
duration of the heat wave. Low temperatures will also be well above
normal, providing little relief from the heat overnight. The hot
temperatures, minimal moisture/low relative humidity values, and
sufficient sustained winds of 20+ mph have also prompted a Critical Fire
Weather Risk area from the Storm Prediction Center on Friday for
south-central Oregon, far northeastern California, and far northwestern
Nevada.

An weakness/disturbance in the upper-level flow between the ridge to the
west and high pressure off the coast of the Carolinas combined with ample
tropical moisture flowing northward from the Gulf over a wavy stationary
boundary will support the development of widespread showers and storms
from Texas east through the Lower Mississippi Valley and into the
Southeast through Saturday. Heavier rainfall totals over portions of Texas
into the Lower Mississippi Valley will pose the risk of flash flooding
both Friday and Saturday. There is a Slight Risk of Excessive Rainfall on
Friday for the Arklatex and Big Bend region of Texas as heavier downpours
may produce hourly rain rates between 2-3". There is also a Slight Risk
for the Texas Gulf Coast into the Lower Mississippi Valley on Saturday for
more widespread heavy rainfall. Areal average totals between 1-2" are
forecast, with localized amounts between 3-5" possible.

Further to the north, the aforementioned cold front over the Northern
Plains will continue southeastward into the Midwest and Great Lakes. The
passage of the front will usher in much cooler temperatures, with highs
only getting into the low 60s for areas around the Upper Great Lakes on
Saturday and the low to mid-70s elsewhere in the region. Notably, areas in
North Dakota will go from highs in the mid- to upper 90s today (Thursday)
to lows in the upper 40s Saturday morning. In addition to the cooler
temperatures, the cold front may tap into enough moisture to produce light
and scattered precipitation and thunderstorms from the Central Plains to
the Upper Great Lakes. Elsewhere, temperatures will be a bit below average
across the the South due to the widespread showers and storms, while highs
will be near normal from the Ohio Valley into the Mid-Atlantic and
Northeast.  

Putnam/Santorelli

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