Climate change in Jefferson County, Missouri
Since 1979, Jefferson County, Missouri has warmed 3.0°F, with 6 more days above 90°F, 9 more nights above 70°F and 8% more precipitation a year. Its climate in 1996–2025 is most like Alexander County, IL's was in 1951–1980.
- Average temperature: +3.0°F
- Summer highs (Jun–Aug): +0.5°F
- Winter lows (Dec–Feb): +4.3°F
- Precipitation: +8%
- Wettest day of the year: +14%
- Longest dry spell: −2 days
- Days above 90°F: +6 days
- Nights above 70°F: +9 days
- Freezing nights: −23 days
- Frost-free season: +25 days
- Muggy days: +11 days
- Summer heat index (Jun–Aug): +1.6°F
- Extreme fire-weather days: +8 days
Changes follow the trend line through every year from 1979 to 2025. Data: NOAA nClimGrid-Daily; humidity from gridMET, adjusted to airport observations.