Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 222359

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
659 PM CDT Fri Sep 22 2023

Issued at 124 PM CDT Fri Sep 22 2023

Through Saturday night...

Key Points:

* Outside of a few lingering showers west of I-39 this afternoon,
  no impactful weather is expected through Saturday night


Combined GOES-16 and 17 water vapor satellite imagery depicts a
fairly busy scene across the contiguous United States with a
tropical storm (Ophelia) nearing the Carolina coasts, a decaying MCV
lifting northeastward from Iowa into southern Minnesota, an active
sub-tropical jet stream arcing into the Southern Plains, and a
sprawling cut-off low pressure system centered over the Pacific
Northwest. Our area is sort of inbetween the "big player" features
(no complaints here), leading to an overall low-impact and
relatively banal forecast.

The only item of note at press time is showers and isolated
thunderstorms continuing to percolate in northwestern Illinois in
the broad warm-air advective regime of the aforementioned
Iowa/Minnesota MCV. As the circulation continues lifting
northeastward this evening, shower coverage should decrease locally
giving way to a dry overnight period. Lingering clouds across
northwestern Illinois will limit overnight radiational cooling with
lows expected to fall toward the 60 degree mark. Elsewhere (e.g.
southeast of I-55 or so), lows should fall into the upper 50s.

Tomorrow looks like a beautiful mid-September day with mostly sunny
skies, light winds, and highs in the mid to upper 70s. With clear
skies tomorrow night, lows into Sunday morning will fall into the
upper 40s to lower 50s, coldest in northwestern Indiana.



Issued at 144 PM CDT Fri Sep 22 2023

Sunday through Friday...

The area looks to be sandwiched between two upper-level lows at
the start of the period which should provide protection from any
shower activity to close out the weekend. However, guidance is
indicating that the western upper-low will begin to drift into the
Mississippi River Valley during the day on Sunday which may allow
a cold front to sneak into western Illinois. While the bulk of
any shower activity should remain west of our area, there is a
developing signal in ensemble guidance that a few isolated showers
may brush areas along and west of I-39 Sunday afternoon and
evening if the low-level dry air can be overcome. Therefore, I
have maintained a slight chance (around 20 percent) mention of
showers in the forecast, but suspect most areas will remain dry
with just increasing mid-level cloudiness.

Heading into next week, the aforementioned blocking pattern is
forecast to begin to break down towards the middle part of the
week which should return rain chances to the region. Guidance has
started to become in better agreement on when the pattern will
break, but continue to very in the location and coverage of any
resultant precipitation. Given this uncertainty I have maintained
the periodic chances (around 20 to 30 percent) for showers through
the period, but suspect many dry hours too. Otherwise, seasonable
temperatures are expected through the period with daily highs in
the 70s and overnight lows in the 50s.



For the 00Z TAFs...

Other than a couple light showers or sprinkles in the RFD area the
first hour or two of the TAF cycle, expect no significant weather
and VFR conditions. Winds will generally remain easterly and less
than 12kt.

- Izzi




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