10-Day Weather Forecast - O'Fallon, IL

Mostly sunny. Isolated showers and thunderstorms this afternoon. Hot with highs around 100. Northwest winds around 5 mph. Chance of rain 20 percent. Heat index values up to 110.

Partly cloudy with isolated showers in the evening, then mostly clear after midnight. Humid with lows in the lower 70s. Northeast winds around 5 mph. Chance of rain 20 percent. Heat index values up to 106 early in the evening.

Mostly sunny. Highs in the lower 90s. Northeast winds 5 to 10 mph.

Mostly clear. Lows in the mid 60s. East winds 5 to 10 mph.

Sunny. Highs in the upper 80s. East winds around 5 mph.

Mostly clear. Hot. Lows in the mid 60s.

Mostly clear. Hot. Highs in the mid 90s.

Mostly clear. Hot. Lows in the mid 70s. Heat index values up to 105.

Mostly clear. Hot. Highs in the upper 90s. Heat index values up to 105.

Mostly clear in the evening, then becoming partly cloudy. A slight chance of thunderstorms. A slight chance of showers in the evening, then a chance of showers after midnight. Lows in the lower 70s. Chance of rain 50 percent. Heat index values up to 100 early in the evening.

Mostly sunny with a slight chance of thunderstorms. A chance of showers, mainly in the morning. Highs around 90. Chance of rain 50 percent.

Partly cloudy in the evening, then mostly clear with a slight chance of showers and thunderstorms after midnight. Lows in the mid 60s. Chance of rain 20 percent.

Mostly sunny with a slight chance of showers. A slight chance of thunderstorms in the afternoon. Highs in the upper 80s. Chance of rain 20 percent.

Clear. Low temperature around 66F. Dew point will be around 64F with an average humidity of 77%. Winds will be 3 mph from the E.

Sunny. High temperature around 89F. Dew point will be around 64F with an average humidity of 58%. Winds will be 3 mph from the S.

Clear. Low temperature around 68F. Dew point will be around 64F with an average humidity of 73%. Winds will be 4 mph from the S.

Sunny. High temperature around 90F. Dew point will be around 65F with an average humidity of 57%. Winds will be 5 mph from the S.

Clear. Low temperature around 69F. Dew point will be around 66F with an average humidity of 74%. Winds will be 4 mph from the S.