Peotone Weather

National Weather Service Forecast for: Peotone, IL Issued by: National Weather Service Chicago/Romeoville, IL

Updated: Fri, 04-Sep-2026 10:21am CDT

- Select Forecast - Peotone, IL Manteno, IL Beecher, IL Monee, IL Kankakee, IL Willmington, IL Braidwood, IL Manhattan, IL OakForest, IL Stelle, IL Ottawa, IL Amboy, IL Byron, IL Rockford, IL Quad Cities, IL Champaign/Urbana, IL Peoria, IL Bloomington, IL Springfield, IL Carbondale, IL Vienna, IL Culver, IN

Peotone, IL

Today Mostly Sunny Saturday Slight Chance Showers And T-Storms then Sunny Sunday Mostly Sunny Labor Day Mostly Sunny Tuesday Partly Sunny Wednesday Slight Chance Showers And T-Storms Thursday Chance Showers And T-Storms then Slight Chance Showers And T-Storms   Hi 92 °F Hi 88 °F Hi 82 °F Hi 83 °F Hi 87 °F Hi 90 °F Hi 84 °F     Tonight Partly Cloudy then Chance Showers And T-Storms Saturday Night Partly Cloudy Sunday Night Partly Cloudy Monday Night Partly Cloudy Tuesday Night Partly Cloudy then Slight Chance Showers And T-Storms Wednesday Night Slight Chance Showers And T-Storms Thursday Night Slight Chance Rain Showers   Lo 71 °F Lo 65 °F Lo 60 °F Lo 62 °F Lo 70 °F Lo 68 °F Lo 62 °F

Heat Advisory issued September 4 at 9:44AM CDT until September 4 at 10:00PM CDT
Heat Advisory issued September 4 at 2:54AM CDT until September 4 at 10:00PM CDT
 

Forecast from NOAA-NWS for Peotone, IL.

653
FXUS63 KLOT 041457
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
957 AM CDT Fri Sep 4 2026

.KEY MESSAGES...

- Today will be another unseasonably hot and humid day with peak
  afternoon heat indices of 100 to 110 degrees.

- Gradually turning cooler and less humid this weekend, though
  remaining seasonably warm.

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

&&

.UPDATE...
Issued at 957 AM CDT Fri Sep 4 2026

Thunderstorms ongoing across southern WI have pushed an outflow
boundary southward into northeastern IL. In its wake, breezy
northerly winds continue to halt the warmth of temperatures this
morning, particularly across far northeastern IL. With this
likely to continue for at least the next 2 to 4 hours, it
appears that conditions (at least across Lake County IL) will be
hard pressed to experience peak heat indices above 100 degrees.
For this reason, we have opted to drop the heat advisory for
Lake County IL for today.

Conditions could also end up largely remaining below heat
advisory criteria (peak heat indices below 100-105) across much
of Cook and possible McHenry counties as well. However, we have
opted to hold onto the heat advisory headline in these areas for
the time being as conditions could quickly heat up this
afternoon as the flow begins to trend back to the west-
southwest. We will continue to monitor observational trends.

KJB

&&

.DISCUSSION...
Issued at 301 AM CDT Fri Sep 4 2026

An unusually strong late season mid-upper level ridge of high
pressure continues to dominate the weather across much of the
central and southern portions of the country east of the
Rockies. Shortwave troughs rotating around the periphery of this
upper ridge continue to support MCS activity in a "ring of
fire" type pattern more reminiscent of mid-summer than early
September.

One such shortwave is noted on water vapor imagery early this
morning just north of International Falls. DCVA in advance of
this shortwave combined with isentropic ascent associated with a
modest 25-30 kt low level jet has led to a couple of small
MCSs. The one of most immediate concern locally is over central
WI, near the nose of the west-southwesterly low level jet. An HP
supercell southwest of Green Bay has developed a bit of a cold
pool and is showing signs of organizing into a small bowing
convective line. Forward propagating Corfidi Vectors, 850-300 mb
thickness, and the instability gradient would all suggest this
developing small bow should remain well north/northeast of our
CWA. However, an outflow boundary from this line could
accelerate down the lake and result in a wind shift to
northeasterly across portions of northeast IL early this
morning. This has been depicted to varying degrees by many CAM
solutions over the past 24 hours.

Absent any significant increase in the size and strength of the
attendant cold pool with the eastern WI MCS, it seems likely
that the lake enhanced outflow should mix out by mid-late
morning with winds turning southwesterly, even right up to the
lakefront by early afternoon. This should set the stage for
another day of unseasonably hot and humid conditions. Given
925mb temps at near record levels in the mid-upper 20s Celcius,
high temps solidly into the low to mid 90s appear likely today.
Pooling dewpoints near and south of the synoptic warm front,
enhanced by late season evapotranspiration should result in
dewpoints in the 70s once again this afternoon. Peak afternoon
heat indices of 100 to 107 degrees are likely this afternoon,
with the typically higher dewpoint more agricultural areas
likely seeing peak heat indices around 110 degrees again this
afternoon.

For this reason, have expanded the heat advisory north to
encompass our entire CWA again today. Heat indices in Chicago
failed to reach 100 degrees yesterday, so the 3+ consecutive day
100+ heat index criteria for an extreme heat warning for Cook
County isn`t going to be met. For our southern CWA, this will be
the 4th consecutive day with advisory level heat indices, which
could justify an upgrade to an excessive heat warning. However,
most nights have had low temperatures dipping into the lower
70s with many hours of relief from the heat at night, so opted
not to upgrade to an extreme heat warning for these areas. Given
the strong instability present and low level jet veering toward
the IL/WI border toward and just after sunrise, certainly
cannot rule out the possibility of some isolated to widely
scattered showers/storms developing near and behind the lake
enhanced outflow boundary early this morning into northeast IL.
However, forcing along this boundary is expected to be pretty
shallow and low level jet likely to weaken diurnally, so threat
of any isolated showers/storms should wrap up by mid-late
morning. The remainder of today should be dry with no forcing
mechanisms for any storms this afternoon.

The upper ridge is expected to begin to retrograde westward
tonight with mid-upper level height falls likely to allow a weak
cold front over the upper Great Lakes to begin moving
southward. The trend in guidance has generally been toward a
slower southward progression, which would make sense given the
expectation of not much convection to our north to aid its
southward push. There is still some signal in HREF guidance for
some convection tonight ahead of this boundary, but with pretty
muted forcing, opted to go with nothing more than 20-30%
chances.

If the progression of the front continues to slow in guidance,
then it is probable that we will need to extend the heat
advisory into Saturday for portions of our southern CWA. Given
that confidence isn`t all that high yet on frontal timing, opted
to defer any advisory extension for the day shift to consider.
Behind the front, it will be somewhat cooler and a bit less
humid, but probably still a bit above average for September.
Temperatures and humidity will continue to moderate on Sunday.

A period of moderately strong northerly winds down the full
fetch of the lake should result in an increase in waves later
Saturday through early Sunday. It is possible that a beach
hazard statement may be needed for dangerous swim conditions for
a part of this weekend, which is the closing weekend of the
beach season.

Dry and seasonably warm weather is expected Labor Day.
Temperatures will warm some and humidity will be on the increase
Tuesday into Wednesday in the warm air advection regime ahead of
the next shortwave. An associated surface cold front could bring
some showers and thunderstorms with it midweek before another
bout of somewhat cooler, more seasonable, temperatures filter in
behind the front to close out the short work week.

- Izzi

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 619 AM CDT Fri Sep 4 2026

Key messages for the 12Z TAF period:

* Wind shift to NE near start of period at Chicagoland sites

* MVFR likely early Saturday

An outflow boundary from prior convection up in Wisconsin is
pushing south across northeast IL as of this writing. It`s
expected to pass over the Chicagoland sites and flip winds to NE
early this morning. ORD is expected to go NE prior to 12Z, MDW
near or shortly after 12Z, and GYY closer to 13Z. They`ll
continue to veer around the compass through the morning and are
expected to return to SW by early afternoon.

A low potential exists for a passing shower or thunderstorm
this evening and tonight. Chances are too low at this time to
warrant any mention in the TAFs.

A cold front dropping in from the north early Saturday will
bring an MVFR deck overhead for the morning and flip light NW
winds to NNE.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 10 PM CDT this evening for ILZ003-ILZ004-
     ILZ005-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-
     ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105-
     ILZ106-ILZ107-ILZ108.

IN...Heat Advisory until 10 PM CDT /11 PM EDT/ this evening for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

Visit us at weather.gov/chicago

NWS LOT Office Area Forecast Discussion