874
FXUS63 KLOT 150507
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1207 AM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Relatively quiet conditions will continue tonight through
  Saturday night.

- Hot conditions are expected Sunday through at least the middle
  of next week with daily highs in the 90s and overnight lows in
  the 70s.

- Daily chances for thunderstorms will return next week, though
  coverage is expected to be isolated to scattered at best.

&&

.DISCUSSION...
Issued at 243 PM CDT Fri Jun 14 2024

Through Saturday night:

A 1020mb surface high pressure system centered over Lake Superior is
leading to quiet conditions across the Great Lakes. A lake-enhanced
cold front continues to push through northeastern Illinois and
will cause temperatures to fall from the mid to upper 80s to the
mid to upper 70s. Meanwhile, a bank of dense fog and very low
clouds is traveling southward along the Illinois Lake Michigan
shoreline, and will reach the northwestern Indiana within the
hour. (It should dissipate within the next few hours).

Tonight looks quiet. A renewed push of winds over Lake Michigan may
cause waves to quickly build to 2-4 or even locally 5 feet, but
felt it would be best to maintain a "Moderate" swim risk given
overnight timing. Otherwise, clear skies and overnight lows in
the mid 50s are expected.

Tomorrow looks similar to today with highs in the low to mid 80s.
With the surface high translating further eastward into Ontario, our
surface winds will turn southeasterly and keep shoreline locations
cooler and in the low to mid 70s.

Tomorrow night, an upper-level shortwave will lift across Iowa and
into southern Wisconsin. A few showers or even a thunderstorm may
attempt to develop across northwestern Illinois overnight,
warranting slight chance (20%) PoPs. Otherwise, it looks like
another relatively quiet, though warmer, night with overnight lows
in the mid 60s.

Borchardt


Sunday through Friday:

The big story of the next week or so is the heat and humidity that is
expected to build into the area as a broad ridge and surface high
set up across the eastern US.

On Sunday, the ridge axis will pass overhead setting up
southwesterly flow. A shortwave is expected to lift across the
backside of the ridge and over the area. The jury is still out on
whether the showers and storms associated with this wave will impact
the CWA. Dry air in the low-levels should inhibit any showers/storms
from developing. Most model guidance keeps us dry on Sunday with
showers/storms moving to the north of the area, with the notable
exception of the GFS. Due to this being a few days out yet and the
possibility of things to change, have left slight chance PoPs for now.

Model guidance is in good agreement with the placement of the ridge
and high pressure with the core setting up in the Mid-Atlantic
before slowly drifting north into the Northeast. With the
progression, we will be on the backside gradient of the ridge,
putting us in play for several shortwave disturbances through the
week. Have gone with slight chance PoPs for almost every day next
week to account for this.

Despite the shortwave moving across the region, Sunday will be the
first day of what looks to be an extended period of seasonably warm
temperatures, however, there are discrepancies between the models as
to how hot it will truly be. The GFS seems to be buying more into
the train of shortwaves with higher dew points (70+ degrees), lower
temperatures (85-90 degrees), and more widespread convection through
the entire week. On the other end of the spectrum, the ECMWF and
Canadian mix dew points out resulting in higher temperatures (95-100
degrees) and dry conditions. Despite the wide variety of
temperatures spit out by the models, the accompanying differences in
dew points result in similar heat indices (95-100 degrees). Monday
is expected to be the hottest day with heat indices approaching or
potentially surpassing 100 degrees areawide. At this point it does
not appear that a heat advisory will be needed, however with
overnight lows only cooling into the mid-70s Sunday night
through Tuesday night conditions will be rather unpleasant.

Conditions will be hot and humid through the remainder of the work
week though not as hot as Monday as the ridge begins to break down
and push off to the east.

Carothers

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1207 AM CDT Sat Jun 15 2024

VFR conditions are expected with no significant aviation
weather concerns. Variable/light NW winds overnight will become
SE just after daybreak. Small potential winds veer 180-190
infrequently at ORD/MDW in the afternoon, but winds are expected
to remain largely east-of-south.

Carlaw

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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