Boulder, CO climate
Boulder has chilly, snowy winters and warm summers, with very little rain. A typical July afternoon reaches 88°, a January night drops to 17°, and about 85 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Boulder feels like
Winter
Spring
Summer
Fall
Boulder weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 46° | 17° | 0.7" | 10.2" | 6 | 25° – 37° |
| February | 47° | 19° | 0.9" | 17.4" | 8 | 28° – 40° |
| March | 56° | 26° | 1.8" | 13.6" | 7 | 36° – 48° |
| April | 62° | 32° | 2.6" | 11.9" | 8 | 42° – 53° |
| May | 71° | 41° | 2.8" | 2.5" | 12 | 50° – 60° |
| June | 82° | 50° | 1.9" | 0 | 9 | 62° – 72° |
| July | 88° | 56° | 1.8" | 0 | 10 | 68° – 76° |
| August | 86° | 54° | 1.7" | 0 | 10 | 66° – 73° |
| September | 79° | 46° | 1.5" | 0 | 7 | 57° – 66° |
| October | 66° | 34° | 1.4" | 6.9" | 7 | 43° – 56° |
| November | 54° | 25° | 1.0" | 8.5" | 5 | 30° – 46° |
| December | 45° | 17° | 0.7" | 14.2" | 6 | 24° – 35° |
| Year | 65° | 35° | 18.6" | 85.2" | 94 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in Boulder
Boulder gets 19 inches of rain and melted snow a year. May is the wettest month and January the driest. Rain or snow falls on about 94 days a year.
About 151 frost-free days a year
In half of years the last 32° night comes by May 6 and the first one by October 5. That leaves about 151 frost-free days for gardens, shorter than 80% of U.S. towns.
Heating and cooling a home in Boulder
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Boulder, 90% of that work is heating and 10% is cooling, so the furnace matters far more than the air conditioner.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
Boulder and its neighbors
Boulder borders 4 towns with climate data. January nights across them vary by 1.8°. Niwot has both the coldest January nights (17°) and the hottest July afternoons (89°). Boulder’s January low is 17° and its July high 88°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Boulder compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in Boulder averaged 1.0° warmer than the 1900s. The biggest change is in March (+2.9°). The shift is smaller than in 67% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Boulder’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. November swings the most: between 1991 and 2020 its average temperature ranged from 30° to 46°. August is the most reliable, staying within 8°.
Common questions about Boulder’s climate
What is the coldest month in Boulder?
December, with a typical high of 45° and a low of 17°.
What is the hottest month in Boulder?
July, with a typical high of 88° and a low of 56°. About 33 days a year reach 90°.
How much snow does Boulder get?
About 85 inches in a normal winter, most of it in February.
When is the first frost in Boulder?
In half of years the first 32° night comes by October 5, and the last spring frost by May 6.
What is the rainiest month in Boulder?
May, with 2.8 inches of rain and melted snow. The year totals 19 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Boulder itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Boulder 2.9 S, CO (2 mi, snow) and Boulder, CO (2 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.