Weather WorldJefferson County, IL 7-Day Night Weather Forecast
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Jefferson County, IL Weather Forecast
Jefferson County, IL Weather Forecast Date: 117 AM CDT Thu Oct 15 2026
The area/counties/county of: Jefferson, including the city of Mount Vernon.or toggle through each period.
Overnight... Mostly cloudy with a slight chance of showers and thunderstorms. Areas of dense fog. Near steady temperature in the upper 60s. Calm winds. Chance of rain 20%.
Thursday... Patchy dense fog in the morning. Mostly cloudy with a chance of showers with a slight chance of thunderstorms in the morning, then partly sunny with showers likely with a chance of thunderstorms in the afternoon. Highs in the mid 80s. Southeast winds 5 to 10 mph, becoming south 10 to 15 mph in the afternoon. Chance of rain 60%.
Thursday Night... A chance of thunderstorms in the evening. Showers likely. Cooler with lows in the upper 40s. Southwest winds 10 to 15 mph, becoming northwest 15 to 20 mph with gusts up to 30 mph after midnight. Chance of rain 70%.
Friday... Partly sunny and breezy. Much cooler. Less humid with highs in the upper 50s. Northwest winds 15 to 25 mph.
Friday Night... Mostly cloudy in the evening, then becoming partly cloudy. Lows in the upper 30s. North winds 15 to 20 mph.
Saturday... Sunny. Highs in the lower 60s.
Saturday Night... Clear. Lows in the mid 30s. Highs in the upper 60s.
Sunday... Clear. Lows in the mid 30s. Highs in the upper 60s.
Sunday Night... Mostly clear. Lows in the upper 30s.
Monday... Partly cloudy. Highs in the lower 70s. Lows in the lower 40s.
Monday Night... Partly cloudy. Highs in the lower 70s. Lows in the lower 40s.
Tuesday... Mostly clear. Highs in the mid 70s. Lows in the mid 40s.
POP = Probability of Precipitation
Jefferson County Radar Loop
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