Jefferson County Climate
Jefferson County, Colorado
Avg Annual Temp
47.7°F
Annual Precip
19.9"
Annual Snowfall
95.9"
Extreme Heat Days
21.47142857142857
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Jefferson County Weather
Jefferson runs 14° cooler than U.S. median
Jefferson County's 47.7°F annual temperature sits 14 degrees below the U.S. median of 61.7°F, reflecting its high-elevation location near Denver's western foothills. Its 19.8 inches of annual precipitation exceed both the state average (16.0 inches) and national average (15.2 inches), making it Colorado's wetter mountain region.
Slightly above Colorado's average
At 47.7°F, Jefferson County runs 1.7 degrees above Colorado's state average of 46.0°F, ranking it in the warmer half of the state's 64 counties. Its 21 extreme heat days annually place it solidly above mountain peers but well below the eastern plains.
Mountain buffer between highlands and plains
Jefferson (47.7°F) sits warmer than the extreme-cold Gunnison and Jackson counties but cooler than the plains-influenced Kiowa and Kit Carson counties to the east. At 21 extreme heat days, Jefferson experiences notably more hot weather than alpine neighbors but far less than eastern counties.
Moderate winters, warm summers, occasional extremes
January averages 30.5°F and July reaches 69.4°F, creating a 39-degree swing with 21 days above 90°F annually. Jefferson receives 95.9 inches of snow yearly, requiring serious winter infrastructure but far less than high-mountain counties.
Balance mountain snow with summer cooling needs
Jefferson residents need reliable heating for winter snowpack (95.9 inches annually) and standard air-conditioning for 21 hot summer days. Spring and fall transition planning is critical for outdoor recreation, with May-September offering prime windows for hiking, water activities, and construction work.
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Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020.
Climate normals are 30-year averages of weather variables computed from 1991 to 2020. Station data is aggregated to county level using spatial averaging. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.