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Simpson Lake, IL Weather Forecast
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Simpson Lake Weather Forecast
| TONIGHT | SUNDAY | SUNDAY NIGHT | MONDAY | MONDAY NIGHT | TUESDAY | TUESDAY NIGHT | WEDNESDAY | THURSDAY | FRIDAY | FRIDAY NIGHT | SATURDAY |
 |  |  |  |  |  | |  | | | | |
| Mostly Clear | Mostly Sunny | Partly Cloudy | Chance of T-Storm | Chance of Showers | Partly Sunny | Partly Cloudy | Partly Cloudy | Partly Cloudy | Partly Sunny | Partly Cloudy | Partly Cloudy |
| Lo: 71°FLo: 22°C | Hi: 99°FHi: 37°C | Lo: 70°FLo: 21°C | Hi: 90°FHi: 32°C | Lo: 65°FLo: 18°C | Hi: 79°FHi: 26°C | Hi: 79°FHi: 26°C Lo: 59°FLo: 15°C | Hi: 79°FHi: 26°C Lo: 59°FLo: 15°C | Hi: 79°FHi: 26°C Lo: 59°FLo: 15°C | Hi: 80°FHi: 27°C | Hi: 81°FHi: 27°C Lo: 59°FLo: 15°C | Hi: 81°FHi: 27°C Lo: 59°FLo: 15°C |
| POP: 40% | POP: 40% |
POP = Probability of Precipitation.
Weather Outlook Updated: 1132 PM CDT Sat Sep 19 2026 
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Issued: 1242 AM CDT Sun Sep 20 2026
Key Messages
- The Heat Advisory remains in effect until early this evening, with high temperatures again reaching the middle to upper 90s this afternoon.
- A cold front will move through our region late today and tonight, allowing much cooler air to gradually filter into our region for the beginning of the work week.
- Temperatures by Tuesday into Tuesday night will be near to a little below seasonal normals, with these conditions persisting the rest of the week and into next weekend.
- 30-60% chances o...