620
FXUS63 KLOT 091729
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1229 PM CDT Wed Sep 9 2026

.KEY MESSAGES...

- Showers and possibly a few isolated thunderstorms this
  morning, shower chances may linger near/south of the Highway
  24 corridor this afternoon into tonight

- Dry weather with seasonable temperatures expected to end the
  work week.

&&

.DISCUSSION...
Issued at 533 AM CDT Wed Sep 9 2026

Vigorous upper level trough noted on water vapor imagery over
the northern Plains early morning with an attendant upper level
jet extending from WY to Lake Superior. Evening ROABs sampled a
nearly 100kt jet in this area. Convection continues to develop
over IA early this morning, in the broad, divergent right
entrance region of this jet. Objective analysis data depicts a
reservoir of 1000+ J/kg of MUCAPE across IA with a 40+ kt low
level jet aimed right into IA. As this convection develops and
pushes eastward into northern IL cloud tops have been rapidly
warming and convection diminishing as it moves east of the nose
of the LLJ and encounters a substantially more stable air mass.

A pair of small MCVs are evident on regional WSR-88d mosaic,
one moving into NW IL just after 07z and a second one over
central IA. The area of rain associated with that lead MCV is
likely to continue weakening and probably gradually dry up as it
reaches lake Michigan. However, this lead MCV will likely
increase moisture in the low-mid levels of the atmosphere and
should allow for the second MCV to maintain itself better as it
moves into and across northern IL later this morning. Still
anticipate minimal instability, but a second wave of rain and
perhaps a couple of isolated thunderstorms (especially western
CWA) should move across northern IL and extreme northwest IN in
the 11-15z time frame.

While the second MCV and its associated rain shield should tend
to weaken later this morning, remnant cloud cover and footprint
of rain cooled air will likely result in the effective frontal
boundary being pushed into our southern CWA by this afternoon.
Cannot rule out some showers continuing into our southern CWA
later this morning into the early afternoon, but coverage is
expected to be on the decrease. Renewed convective development
this afternoon appears unlikely across IL given the lack of
forcing and weak instability.

Another shortwave over the northern Rockies is expected to
shear rapidly eastward into the lower Missouri River Valley
later tonight, likely resulting in an uptick in coverage of
showers and thunderstorms over Missouri late tonight. As this
activity pushes east into Illinois, it is possible that the
northern flanks of the showers could scrape across our far
southern CWA late tonight into Thursday morning, but the vast
majority of this rain and all of the associated thunderstorm
activity should stay south of our area.

Temperatures today will be heavily dictated by cloud cover with
highs potentially topping out in the lower 80s far southern CWA
prior to thicker cloud cover and potential showers. Also, far
northwest CWA could see highs in the lower 80s assuming some
partial clearing this afternoon. Over the majority of the CWA,
highs will probably hold in the 70s given the cloud cover.

Other than the small chance of showers near/south of Highway 24
in the morning, Thursday looks to be a pretty nice day weather-
wise across the area. Skies are expected to clear out, lower
dewpoints will advect in, and highs will top out in the 70s. By
Thursday night, the center of the high pressure ridge should set
up over the area. This should set the stage for nearly ideal
radiational cooling with clear skies and calm winds. Have nudge
low temps downward Thursday night, especially in the typical
cool spots where lows could dip into the 40s. The urban heat
island should keep the heat of the city of Chicago in the lower
60s for low temps. Friday looks like another spectacular early
autumn day with highs around 80, low humidity, and sunny skies.

The weekend forecast overall looks ok, though forecast
confidence is a bit lower with some chance it could rain a bit
at some point. Another trough is expected to pass well north of
the area over the weekend with a weakening cold front reaching
the area Saturday or Saturday night before probably washing out
altogether. Cannot totally rule out a few showers with that
front, but given weak frontal convergence, antecedent dry air
mass, and minimal upper forcing, the more likely scenario looks
to be dry weather for most. Southerly winds in advance of this
front should allow temps to warm more solidly into the 80s on
Saturday. Another trough is expected to move into the region
early next week bringing what looks to be a somewhat better
chance of showers and thunderstorms in the Monday/Tuesday time
frame. There is still model variability in the timing and track
of that trough, so forecast confidence is still on the lower end
of the spectrum.

-Izzi

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1228 PM CDT Wed Sep 9 2026

Key Aviation Messages for the current TAF period:

- MVFR cigs linger through this afternoon. Moderate confidence
  on timing of improvement to VFR

Winds are currently out of the west around 10 knots. Most rain
showers have dissipated for many terminals with linger showers
south of a KVYS to KVPZ line. Most terminals remain under a
broad area of MVFR cigs between 1000-1500 ft AGL, though
isolated pockets of IFR cigs are occurring. There is lower
confidence in IFR trends at any one terminal. However, as a
front (observed on satellite imagery currently over southern
Wisconsin) continues to move south over the region, VFR should
return to all TAF sites by the late afternoon. Specific timing
may be adjusted, but there is moderate confidence given latest
satellite trends.

A drier period is in store for the TAFs beginning at 00Z
tonight. VFR conditions are expected to prevail. As winds
lighten this evening, they will turn to the northwest and
eventually to the northeast around and after daybreak. There is
the chance for a lake breeze to push inland tomorrow afternoon
providing more easterly wind directions at Chicago terminals.

DK

&&

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

&&

$$

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