354
FXUS63 KLOT 051720
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1220 PM CDT Sat Sep 5 2026

.KEY MESSAGES...

- Hot again today away from the lake with afternoon heat indices
  in the 90s, and as high as 100 to 105 south of the Kankakee
  and Illinois river valleys.

- Relatively cooler early next week, although remaining
  seasonably warm.

- Moderate to high swim risk expected late Saturday into early
  Sunday during the final weekend of beach season.

&&

.DISCUSSION...
Issued at 211 AM CDT Sat Sep 5 2026

It`s an unseasonably warm start to our Saturday with
temperatures across most of the area still sitting in the middle
to upper 70s as of 2 AM. A cold front is gradually inching
south across the area as we speak. The placement of the front
isn`t terribly defined, but it looks to be draped roughly along
the I-88 corridor. There isn`t much of a cold advective response
immediately behind the boundary, but slightly cooler temps in
the lower 70s are found north of the front across our northern
CWA and up into southern WI. A few thunderstorms traversed our
northern CWA along the boundary late last evening driven by a
midlevel shortwave impulse scooting east atop the area. That
wave has since moved away to the east and taken the precip
coverage with it, but a reservoir of elevated instability
remains over the area and it`s possible that a light shower or
even isolated thunderstorm develops along the boundary early
this morning as it progresses south. A general lack of forcing,
however, will largely inhibit precip development this morning.
We are seeing some areas of fog developing in the wake of the
front up in southern WI. Nothing too dense has been observed nor
is expected, but it`s possible that some visibility reductions
spread into northern IL early this morning north of I-80.

Mixing into relatively cooler, northerly BL flow today will
keep temperatures a couple to a few degrees cooler than
yesterday with highs forecast in the middle 80s to lower 90s
across inland areas. The warmest temperatures and highest
dewpoints are forecast in our far southern CWA where afternoon
heat indices may approach 105. Expectations are for largely
closer to 100 though, so opted against issuing any heat
headlines for today. Elsewhere across inland areas, forecasting
heat indices throughout the 90s today. It`ll be a different
story near the lakeshore where the onshore flow will bring
noticeably cooler conditions than yesterday with afternoon
temperatures forecast in the 70s up to a few miles inland from
the lake.

The breezy northerly fetch will also generate choppy conditions
on the lake this evening into early tomorrow. Will continue to
advertise a Moderate Swim Risk for now as waves generally look
to top out in the 2 to 4 foot range, but expectations are not
far from warranting a High Swim Risk for a period this weekend,
especially at northwest Indiana beaches.

The midlevel ridge will center itself over the region early
next week shunting any meaningful baroclinicity well away for a
few days. Highs in the lower 80s are forecast for tomorrow and
Monday with mostly sunny skies. Upper 80s and lower 90s are
favored again for the middle part of next week with scattered
chances for rain returning as early as Tuesday night.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1220 PM CDT Sat Sep 5 2026

Key Messages:

- Low MVFR cloud bases gradually improve through the afternoon.

- Threat for some ground fog at DPA and RFD around, daybreak
  Sunday morning.

A deck of IFR to low end MVFR stratus continues to shift into
the area on northeasterly winds early this afternoon. While
this cloud cover is expected to persist this afternoon, bases
are expected to gradually improve through the remainder of the
day, with VFR conditions potentially returning at most
terminals after 20Z.

Some patchy ground fog is then possible early Sunday morning at
DPA and RFD. Otherwise, expect quieter weather during the day
Sunday, with east-northeasterly surface winds.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 7 PM CDT this evening for ILZ032-ILZ033-
     ILZ039.

IN...Heat Advisory until 8 PM EDT this evening for INZ019.

LM...None.

&&

$$

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