Weather Alert
St Clair County Weather Warning NWS WEATHER ALERT FOR THE ST CLAIR COUNTY, IL AREA - Issued: 219 AM CDT Thu Sep 17 2026 St Clair County Weather Warning

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St Clair County, IL Weather Forecast

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St Clair County, IL Weather Forecast

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St Clair County IL weather - Clear - 72°F
Clear
72°F
Updated 5:50 am
Feels Like 82°F
Humidity 100%
Wind N 0 mph
Barometer  30.2 in
Dew Point 72°F
St Clair County IL weather - Clear - 22°C
Clear
22°C
Updated 5:50 am
Feels Like 28°C
Humidity 100%
Wind N 0 km/h
Barometer  102.3 kPa
Dew Point 22°C
WX Settings

St Clair County Weather Forecast

TODAY TONIGHT FRIDAY FRIDAY NIGHT SATURDAY SATURDAY NIGHT SUNDAY SUNDAY NIGHT MONDAY MONDAY NIGHT TUESDAY TUESDAY NIGHT
St Clair County, IL Weather - Today Chance Of T-Storm St Clair County, IL Weather - Tonight Chance Of T-Storm St Clair County, IL Weather - Friday Chance Of T-Storm St Clair County, IL Weather - Friday Night Mostly Clear St Clair County, IL Weather - Saturday Mostly Sunny St Clair County, IL Weather - Saturday Night Chance Of T-Storm St Clair County, IL Weather - Sunday Chance Of T-Storm St Clair County, IL Weather - Sunday Night Chance Of T-Storm St Clair County, IL Weather - Monday Chance Of T-Storm St Clair County, IL Weather - Monday Night Chance Of Showers St Clair County, IL Weather - Tuesday Chance Of Showers St Clair County, IL Weather - Tuesday Night Partly Cloudy
Chance of T-Storm Chance of T-Storm Chance of T-Storm Mostly Clear Mostly Sunny Chance of T-Storm Chance of T-Storm Chance of T-Storm Chance of T-Storm Chance of Showers Chance of Showers Partly Cloudy
Hi: 99°FHi: 37°C
 Lo: 71°FLo: 22°C Hi: 95°FHi: 35°C
 Lo: 71°FLo: 22°C Hi: 95°FHi: 35°C
 Hi: 91°FHi: 33°C
Lo: 71°FLo: 22°C		 Hi: 91°FHi: 33°C
Lo: 71°FLo: 22°C		 Lo: 69°FLo: 21°C Hi: 85°FHi: 29°C
 Lo: 61°FLo: 16°C Hi: 80°FHi: 27°C
 Hi: 81°FHi: 27°C
Lo: 60°FLo: 16°C
POP: 20% POP: 20% POP: 20% POP: 20% POP: 20% POP: 40% POP: 50% POP: 50% POP: 20%
POP = Probability of Precipitation.
Weather Outlook Updated: 237 AM CDT Thu Sep 17 2026 St Clair County, IL Weather - WeatherWorld.com

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Issued: 243 AM CDT Thu Sep 17 2026

Key Messages

  • A late season heat wave continues through at least Saturday with peak heat index values of 100-105F+ along/south of I-70.
  • Scattered showers with an isolated sub-severe thunderstorm are possible (20-30%) across portions of the area this afternoon/evening.

Aviation

/00Z TAFS THROUGH 06Z FRIDAY/... Issued at 1108 PM CDT Wed Sep 16 2026

VFR flight conditions are expected to prevail through the period. Light and variable surface flow will turn to the west- southwest Thursday morning across m...