Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Tue Sep 07 2021

Valid 12Z Tue Sep 07 2021 - 12Z Thu Sep 09 2021

...A heat wave will encompass much of the West with record high
temperatures possible...

...A strong cold front will bring the threat of locally heavy rains and
severe weather across the Great Lakes through tonight...

A mid- to upper-level ridge is expected to strengthen and expand its
influence across the western U.S. during the next few days, setting the
stage for widespread much above average temperatures across the region. 
Heat advisories are currently in effect across large sections of
California while Excessive Heat Warnings are in effect for the Mojave
Desert.  High temperatures are forecast to remain above 100 degrees for
the next couple of days, with 120 degrees possible in Death Valley. 
Record high temperatures are possible in the interior valleys of
California, across portions of the Great Basin, spreading into the central
High Plains on Thursday.  In addition to the heat, there will also be a
fire weather threat across large portions of the west where no
precipitation is expected over the next several days, which will
exacerbate the ongoing extreme to exceptional drought conditions.

As the ridge builds across portions of the west, a mid- to upper-level
trough will be amplifying downstream over the Great Lakes and into the
Ohio Valley.  This will propel a strong cold front through the Great Lakes
today.  Organized thunderstorms are anticipated ahead of and along this
front, bringing the threat of locally heavy rains, isolated flash flooding
and the risk of severe weather through the central Great Lakes today
before reaching the lower Great Lakes later tonight.  On Wednesday, much
of the East Coast will see an increasing chance of thunderstorms
especially later in the afternoon into the evening as the cold front
pushes steadily through the region.  By Thursday morning, the best chance
of showers and storms will be across eastern New England ahead of the
front while drier air will begin to filter into the Mid-Atlantic behind
the front.  In the wake of this cold front, cooler than average high
temperatures are expected to overspread the northern Plains, upper
Mississippi Valley and upper Great Lakes region today, and then across all
of the Great Lakes, Ohio Valley into the Upper Mississippi Valley on
Wednesday.

Elsewhere, showery conditions can be expected along the Gulf coast,
Southeast and Florida, along and to the south of a weakening frontal
boundary across the Southeast.  Some increase of thunderstorm activity is
possible near the eastern Gulf Coast on Wednesday as a modest amount of
moisture associated with a tropical wave could be drawn northward from
over the Gulf of Mexico.

Kong/Oravec