326
FXUS01 KWBC 221220
PMDSPD

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
819 AM EDT Sat Jun 22 2024

Valid 12Z Sat Jun 22 2024 - 12Z Mon Jun 24 2024

...Heat wave focus shifts from the Midwest/Ohio Valley into the
Mid-Atlantic states this weekend...

...Heavy rain and flash flooding concerns across the Upper Great
Lakes/Mississippi Valley Saturday and northern New England
Sunday...

...Heat building across the West this weekend, monsoon-like
conditions for the Desert Southwest...

A heat wave will continue over much of the eastern U.S. south of a
quasi-stationary boundary and under the influence of longwave
ridging aloft this weekend. Forecast high temperatures Saturday
will generally be in the mid- to upper 90s from the
central/southern Plains to the East Coast. These temperatures
remain the most anomalous and dangerous for early Summer over
portions of the Midwest/Ohio Valley east to the Mid-Atlantic.
Heat-related advisories and warnings are in place as humidity will
bring heat index values as high as the mid-100s. A potent
upper-level shortwave will help to finally push the boundary
southward Sunday, bringing welcome relief to much of the
Midwest/Ohio Valley, while the Mid-Atlantic continues to simmer.
Numerous record-tying/breaking highs are possible. In addition,
overnight low temperatures will remain to the mid- and even upper
70s, providing little relief from the heat overnight. The
combination of this heat coming early in the Summer season and
persisting over several days increases the level of heat stress
for those without reliable air conditioning.

Widespread showers and thunderstorms will continue to the north
along the quasi-stationary boundary draped from New England west
through the Great Lakes and into the Upper Mississippi Valley.
Plentiful moisture will increase the chance for locally heavy
downpours. The highest chance for potentially significant heavy
rainfall will be along the boundary ahead of an upper-level wave
over portions of the Upper Great Lakes/Upper Mississippi Valley
Saturday. Ongoing organized storms from overnight Friday as well
as the risk for more widespread, organized storms into the day
Saturday has prompted a Moderate Risk of Excessive Rainfall (level
3/4) over southern Wisconsin and northeastern Iowa for the threat
of scattered to numerous instances of flash flooding. A broader
Slight Risk (level 2/4) covers the region. In addition, a few
storms may be severe, with a Slight Risk of severe weather (level
2/5) issued by the Storm Prediction Center for the threat of some
damaging winds and a few tornadoes. A locally higher threat for
heavier downpours will also exist over southern New England, with
a Slight Risk in place. The noted more potent upper-level
shortwave arriving Sunday will help to push the boundary south and
eastward, bringing higher storm chances more broadly across New
England and southwestward though the Mid-Atlantic/Ohio
Valley/Tennessee Valley. Stronger, very moist low-level flow
interacting with the boundary over northern New England will bring
the greatest chance for heavy downpours and scattered flash
flooding, with another Slight Risk in place. A Slight Risk for
severe weather also covers much of the same region and
southwestward into the northern Appalachians/Upper Ohio Valley,
where damaging winds and a few tornadoes will once again be the
main threats.

Upper-level ridging will begin to build over the western and then
central U.S. following the shortwave passage, bringing rising
temperatures across this region as well. Forecast highs Saturday
across much of the interior Pacific Northwest, Great Basin, and
California will be in the mid-90s to low 100s. Locally higher
temperatures into the mid-100s have prompted heat-related
advisories and warnings for the central California Valleys into
portions of southern California. The focus over the northern tier
will begin to shift eastward with the ridge on Sunday, with cooler
highs in the Pacific Northwest but temperatures soaring into the
mid- and upper 90s over much of the central/northern High Plains.
Conditions will remain hot from central to southern California.
Temperatures will still be hot but closer to average for the
Desert Southwest as Monsoon-like conditions remain over the
region. Highs Saturday and Sunday will range in the mid- to upper
100s, with scattered showers and storms bringing the threat for
some locally heavy downpours and an isolated risk for flash
flooding. Elsewhere, a pair of waves of low pressure passing over
portions of the Southeast/Florida as well as south Texas will
bring daily shower and storm chances.

Putnam


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