266
FXUS63 KLOT 160832
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
332 AM CDT Wed Sep 16 2026

.KEY MESSAGES...

- Waves of showers and storms are expected in the general
  region through much of the week.

- While some areas may not see much rain at all, others may
  experience repeated downpours with a threat for localized
  flooding.

- The next few days will also be marked by high humidity.

- Another period of showers and storms is favored in the general
  region Friday night through the weekend.

&&

.DISCUSSION...
Issued at 332 AM CDT Wed Sep 16 2026

A parade of convectively enhanced mid-level impulses continues
to drive waves of convection early this morning as they track
east-northeastward along the northern periphery of the
subtropical ridge parked over the Southeast. Most of the
convection overnight has been focused mainly south of the I-80
corridor from northern MO eastward into west-central
ILessentially along the northern terminus of a ~30kt
southwesterly low-level jet (per area VAD wind profiles). While
showers and storms have been more widely scattered in our area
thus far early this morning, a wave of more widespread showers
and storms is quickly moving into western sections of our area
as of this writing. The primary threat of thunderstorms and very
heavy rainfall will remain south of I-80 with this wave through
around daybreak. Farther north, the Chicago metro area will
reside along the northern periphery of this wave, though a
period of lighter rain remains likely through daybreak,
particularly across southern sections of the metro.

Following this initial early morning period of showers and
storms, chances for scattered showers may persist at times
through the day as remnant upstream convectively enhanced
impulses track eastward into the lower Great Lakes. However, the
overall threat and coverage of thunderstorms during the day
should remain low, with the main chances this afternoon staying
to our south closer to the better MUCAPE. Cloudy skies and
northerly surface flow will result in another cool early-autumn
day, particularly along and north of I-80 where temperatures
will once again remain in the lower 70s. Farther south into
central portions of IL and IN, closer to the surface frontal
boundary, a warm and humid afternoon is expected.

Another round of heavy rain-producing showers and thunderstorms
is likely to develop tonight into early Thursday morning,
though not everyone will be impacted by the heavy rain. Instead,
a corridor of eastward-training storms is likely to develop
later this evening along the nose of an intensifying
southwesterly low-level jet. Initially, it appears this corridor
of storms will focus across eastern IA. However, as the low-
level jet veers overnight, the focus may expand east-
southeastward into portions of our area. These setups are always
tricky, as forecast guidance rarely depicts the precise
location of the heaviest rain axis and frequently places it too
far north. With this in mind, current thinking is that the
heaviest rainfall axis may remain largely south of the I-80
corridor, as depicted by the 00Z HREF. Wherever this favored
corridor for training storms sets up late tonight into early
Thursday morning, heavy rainfall could result in localized
instances of flash flooding.

A period of drier weather is expected Thursday afternoon through
at least the first half of Friday as surface high pressure
building into the Upper Great Lakes briefly pushes the surface
frontal boundary well south of our area. East-northeasterly
surface winds will yield seasonable temperatures in the 70s on
both Thursday and Friday. Shower and storm chances will return
late Friday as the next notable shortwave ejects from a
Southwest trough across the western Great Lakes. At this point,
the best shower and storm chances late Friday into Friday night
look to remain largely across WI, extending possibly as far
south as portions of far northern IL (north of I-88). Better
chances will return to most of our area over the weekend as the
next cold front sags southward into the area. Continued very
high atmospheric column moisture (precipitable water values near
2") will also bring another threat of locally heavy rainfall
with these weekend storms.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1249 AM CDT Wed Sep 16 2026

Main Concerns:

- A period of -RA early this morning.

- Lower flight category trends, including potential for low MVFR
  to IFR tonight into early Thursday morning.

- Additional SHRA and embedded TS tonight into early Thursday,
  though better potential may focus south of the terminals.

Spotty showers may occur near the terminals any time early this
morning. However, the most favored timing is from the pre-dawn
hours to mid morning on the northern edge of activity over
western/west central IL as of this writing. It appears any
embedded TS will remain primarily south of the terminals. Best
chance for reduced VSBY with the rain is at GYY.

CIGs are likely to deteriorate to MVFR today, with lower
confidence in exact details, and mostly maintained previous TAF
timing. Overnight into early Thursday, some of the guidance
suggests CIGs and VSBY lowering to IFR and even LIFR in spots.
The northern extent of SHRA and TS over the region is again
uncertain, though latest thinking is that TS chances are higher
south of the terminals. Given the overall uncertainty,
confidence in rain is low, but opted for a PROB30 at ORD and
MDW to also highlight the lower CIGs and VSBY. Expect generally
northeasterly winds for most of the period, becoming light/VRB
to calm in spots early Thursday.

Castro

&&

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

&&

$$

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