621
FXUS01 KWBC 211855
PMDSPD

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Fri Jun 21 2024

Valid 00Z Sat Jun 22 2024 - 00Z Mon Jun 24 2024

...Record hot temperatures over portions of the Midwest/Ohio
Valley & the Mid-Atlantic states this weekend...

...Heavy rain and flash flooding concerns across the Upper Midwest
Friday night and Great Lakes Saturday...

...Monsoon-like conditions for this Southwest this weekend into
Monday...Heat building across the West...


A heat wave should continue for portions of the Midwest/Ohio
Valley and the Mid-Atlantic States, to the south of a stationary
front. Forecast high temperatures will rise into the upper
90s/near 100 Saturday in the Mid-Atlantic, with
record-tying/breaking temperatures possible. Heat-related
Advisories and Warnings are in place as these temperatures, when
combined with the humidity, will bring heat index values into the
100-105 degree range, with values as high as 110 possible through
the southern Mid-Atlantic on Saturday. Additionally, overnight low
temperatures will remain in the mid-70s for many locations, at
potential record-tying/breaking levels, providing little relief
from the heat. The early arrival of this heat in the Summer
season, persistence over multiple days, and abundant sunshine will
aggravate heat stress on those without reliable air conditioning.
Temperatures more broadly from the East Coast to the
central/southern Plains will be in the mid-90s this weekend.
Meanwhile, relief continues to the north of a frontal boundary
draped though southern New England, with highs now mostly in the
70s and low 80s.  Isolated to scattered excessive rainfall/flash
flooding is possible near the stalled frontal boundary.

The greatest threat for significant heavy rainfall will be ahead
of a surface wave over portions of the Upper Midwest as
thunderstorm complexes late on Friday unleash their potential.  A
Moderate Risk of Excessive rainfall (level 3/4) is in effect, from
southeast South Dakota to in and near the Minnesota/Iowa border,
where the highest potential for heavy rainfall/significant flash
flooding exists.  Moderate to major river flooding is also
forecast to worsen.  Additional scattered instances of flash
flooding will be possible more broadly across the Upper Midwest.
An upper-level shortwave approaching from the west will help to
deepen the frontal wave and push the system eastward on Saturday,
bringing the threat for heavy rainfall/flash flooding to portions
of the Great Lakes southwestward into the Upper Mississippi Valley
as an organized complex of storms is expected to follow the system
eastward.  Some severe thunderstorms will again be possible with a
Slight Risk in place mainly for the threat of damaging winds.  As
the system pushes into New England on Sunday, it brings an
elevated risk of flash flooding to the region.

Near the Southeast Coast, a small convective low has the potential
to bring isolated heavy rainfall/flash flooding over the next
couple of days as it moves inland into portions of far northeast
Florida and Southeast Georgia.  The National Hurricane Center is
monitoring it for tropical cyclone development, as it has a 60%
chance to become a tropical depression prior to landfall Friday
night into Saturday morning.  Across the southern Gulf of Mexico,
another tropical disturbance has a 60% chance of formation into a
tropical depression over the next 2-3 days, and it brings a risk
of isolated flash flooding this weekend to areas which received
heavy rainfall from Alberto on Wednesday.

The warm core high across the Mid-South is expected to shift into
the West with time, towards the Four Corners.  When combined with
moisture brought into the region by the former tropical storm
(Alberto), whose remains will be moving west-northwest from
southern Baja California into the open North Pacific, monsoon-like
afternoon and evening thunderstorms are expected with associated
locally heavy rainfall/flash flooding, which would be most
problematic in dry washes/arroyos, slot canyons, and locations
with burn scars.  Some of the storms could also cause haboobs --
dust storms caused by strong, cool thunderstorm outflow.  Forecast
highs will soar into the 100s on Saturday for portions of the
Great Basin and central California Valleys, bringing high
temperatures close to record values across northern California and
portions of Utah. Heat-related Advisories and Watches have been
issued for the central Valleys south into interior southern
California. Conditions will also be notably hot over the Desert
Southwest on Friday, particularly over central Arizona where
Excessive Heat Warnings are in place, with highs into the 110s.

Roth/Putnam


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