747
FXUS63 KLOT 080720
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
220 AM CDT Tue Sep 8 2026

.KEY MESSAGES...

- Showers and some thunderstorms are expected later tonight
  into Wednesday.
- Temperatures will remain near to above average through the
  upcoming weekend, warmest today and then again over the
  weekend.

&&

.DISCUSSION...
Issued at 220 AM CDT Tue Sep 8 2026

The upper ridge that has been responsible for our near record
warm first week of September is poised to be suppressed
southward a bit mid week as a pair of shortwave troughs pass by
to our north. These two shortwaves show up nicely on water vapor
imagery early this morning as a pair of closed circulations
embedded with a broader trough extending from southern
Saskatchewan into the Pacific Northwest. Associated sfc low will
track east into Manitoba today with a cold front trailing south
into the lower Missouri Valley by later this afternoon.

Out ahead of this system, southern winds will become
established across our CWA today leading to another unseasonably
warm day. Despite cirrus cloudiness obscuring the sun a bit,
still anticipate high temps to climb into the mid to upper 80s
today. With deeper low level moisture pooled ahead of the
boundary to our west, we could see dewpoints mix out some this
afternoon, especially eastern CWA, which should keep heat
indices near or a hair below ambient temperatures.

Convection is expected to develop over IA this afternoon ahead
of the cold front in an area of maximized instability and
moderate shear. This convection is expected to move eastward
into northern Illinois tonight, but as it does so, it will be
moving into a more stable environment with less moisture. In
addition, the lead shortwave will be lifting farther northeast,
becoming even more removed from what will likely be a decaying
convective complex moving into northern IL overnight. The low
level jet is expected to be focused to our north and also not be
of much assistance in maintaining the intensity of this MCS as
it moves into our area. With MUCAPE expected to be 500 J/kg or
less, there may not be much thunder left with this activity as
it moves into our area.

The remnants of that activity could linger into Wednesday
morning over our area, mainly bringing a threat of showers
without much threat for thunder. Wednesday`s set-up looks
potentially pretty messy, with the potential for outflow from
this prior convection resulting in an effective frontal boundary
setting up over central IL into north central Indiana Wednesday
afternoon, well ahead of the synoptic cold front which is
progged to move into northern IL during the afternoon. Mid and
upper level height falls in advance of trailing shortwave trough
is likely to support renewed convective development Wednesday
afternoon into Wednesday evening, but it isn`t clear if the more
widespread and stronger convection will be over central IL with
the lead outflow boundary or if the air mass in the wake of
that boundary will recover sufficiently allowing the true
synoptic cold front to be the primary focus for late day into
evening storms.

Mid-level lapse rates should remain pretty weak Wednesday,
limiting instability despite 70F+ dewpoints likely to be pooling
near and ahead of the boundary/boundaries. That degree of low
level moisture is still likely to support an axis of 1000-1500
J/kg of MLCAPE (given sufficient heating/breaks in the
cloudiness). The moderate instability paired with respectable
deep layer shear around 40kt, could lead to a localized threat
for severe storms Wednesday afternoon, particularly over our
southern CWA as it looks now. The showers and thunderstorms
should gradually settle south of our CWA Wednesday night as the
synoptic front pushes south of the area.

In the wake of the front, look for a brief cool down and return
to temperatures closer to average Thursday. Warm air advection
is already progged to start ramping up Friday in advance of the
next shortwave, allowing temps to warm a bit Friday and more so
into Saturday. The next cold front should move across the
region later Saturday or Saturday night bringing with it the
next chance of showers/storms followed by another return to near
average temps late in the weekend into early next week.

- Izzi

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1232 AM CDT Tue Sep 8 2026

Key messages for the 06Z TAF period:

* Showers and perhaps a couple of thunderstorms near and beyond
  the end of the 30 hour TAF period.

Light SE winds will gradually veer through the night and should
favor a SSW direction after about 14Z. A lake breeze will
protrude inland during the afternoon but may hold just short of
the Chicago sites. If it does make it across, a period of SSE is
likely during the late afternoon. Wind speeds during the day
should be near and largely below 10 kt.

A system of showers will approach from the NW early Wednesday
morning. Showers may reach Chicagoland as early as around
daybreak, but chances increase after 12Z and stick around
through the morning. A couple of embedded thunderstorms and
periods of MVFR will be possible, mainly after 12Z.

Doom

&&

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

&&

$$

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