133
FXUS63 KLOT 212341
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
641 PM CDT Mon Sep 21 2026

.KEY MESSAGES...

- Below average temperatures expected for the remainder of the
  work week.

&&

.DISCUSSION...
Issued at 155 PM CDT Mon Sep 21 2026

A strong (1031 MB) high over Lake Superior is helping produce rather
brisk northeast winds which have been ushering in cooler
temperatures and gradually lower dewpoints. A closed mid-upper level
low seen on water vapor imagery is moving into western IA early this
afternoon. This upper low is expected to slowly weaken as it pushes
east into northern IL by midday Tuesday. The unseasonably moist air
mass that helped feed heavy rainfall totals over the weekend is
being shunted off to the south of the area. However, cold mid-level
temps (around -15C) associated with this weakening upper low should
be enough to result in scattered showers this afternoon across IA.
This shower activity is expected to attempt to spread east into
northern IL late tonight into Tuesday morning as the upper low
pushes this way, however, the showers are expected to encounter a
gradually drier air mass as they move east of the MS River. Have
maintained some 20-30% chances for showers late tonight into Tuesday
AM, especially across our western CWA.

This shortwave trough is progged to continue eastward toward the
East Coast by Wednesday into Wednesday night, likely aiding in
intense coastal cyclogenesis. A Rex Block is expected to develop
over southeastern Canada into the Great Lakes later this week as a
strong, large cut-off coastal cyclone becomes quasi-stationary to
the south of a strong mid-upper high over southeastern Canada. For
our area, this should result in an extended period of somewhat
cooler temperatures and very little threat of precipitation from mid
week through the upcoming weekend. One small possible exception to
the dry weather could be Wednesday morning into the Chicago Metro
area when there could be a few sprinkles or very light lake effect
rain showers. Thermodynamics are marginal and with fairly dry low
level air mass, the chances appear pretty small so didn`t introduce
any precip into the grids at this time, but did nudge pops up to
around 10%. Otherwise, look for temperatures that will likely slowly
moderate late in the week into the weekend with temperatures
probably warming back into the 70s.

- Izzi

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 641 PM CDT Mon Sep 21 2026

There are no significant aviation forecast concerns for the
current TAF period.

Patchy MVFR ceilings are still being observed at and near ORD
and RFD at press time and may linger in the area for a while
longer this evening. Additional periods of MVFR ceilings appear
to be possible at times tomorrow, though prevailing VFR
conditions are still favored at all of our TAF sites over the
course of the TAF period.

Light rain will likely persist at and near RFD through this
evening. An additional wave or two of rain showers may pass
over or near RFD again tomorrow, and sprinkles or a brief period
of rain showers may also occur at ORD and MDW towards the end
of their current 30-hour TAF period, but will let the potential
need for additional precipitation mentions in the TAFs be
addressed in forthcoming TAF issuances.

Otherwise, expect persistent northeasterly winds throughout the
TAF period with gusts to around 20 kts at times.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through Wednesday evening for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement through Wednesday afternoon for INZ001-
     INZ002.

LM...Small Craft Advisory until 7 PM CDT Wednesday for the IL
     nearshore waters.

     Small Craft Advisory until 10 AM CDT Wednesday for Calumet
     Harbor IL to Burns Harbor IN.

     Small Craft Advisory until 7 PM CDT this evening for Burns
     Harbor to Michigan City IN.

&&

$$

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