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Boulder, CO Weather by Month and Climate Averages
Monthly normals · Rain · Snow
Sunshine · Freeze dates · Records · Best time to visit
What is the weather like in Boulder, CO?
Boulder, CO gets 21.2 in of precipitation a year over about 101 rainy days, and about 92.8 in of snow a season. July is the warmest month (average high 88°F) and January the coldest (average low 22°F).
Humid subtropical climate
Boulder, CO has hot summers and chilly winters. Daytime highs range from about 46°F in December to 88°F in July. May is usually the wettest month, and snow falls in winter. The most comfortable time to visit is typically April and September to October, when daytime highs sit near 69°F.
| Season | Months | Avg low | Avg high |
|---|---|---|---|
| Winter | Dec–Feb | 22° | 47° |
| Spring | Mar–May | 36° | 64° |
| Summer | Jun–Aug | 55° | 85° |
| Autumn | Sep–Nov | 38° | 66° |
How much rain does Boulder get?
Boulder gets 21.2 in of precipitation in an average year, spread over about 101 days with measurable rain. That is more rainy days than 61% of the US.
May is the wettest month, with 3.2 in. December is the driest, with 0.8 in. May has the most rainy days, about 13.
The longest dry spell in the last five years lasted 25 days, to October 17, 2024.
From September 2025 to August 2026 Boulder got 16.9 in of rain, against a normal of 21.2 in for those months. September 2025 had the most, with 4.0 in.
See where Boulder ranks: rainiest cities in the US, US cities with the most rainy days, rainiest cities in Colorado.
Does it snow in Boulder?
Yes. Boulder gets about 92.8 in of snow in an average season, measured at the reporting station.
The snowiest winter on record is 2019–20, with 152.0 in.
The most recent measurable snow at the station fell on May 6, 2026.
From September 2025 to August 2026 the station measured 41.4 in of snow, against a normal of 92.8 in for those months. December 2025 had the most, with 12.0 in.
See where Boulder ranks: snowiest cities in the US.
Boulder weather by month
Boulder weather in January
In January, Boulder averages a high of 47°F and a low of 22°F. It gets 0.8 in of precipitation over about 6 rainy days. Estimated sunshine is 52% of daylight hours, derived from ERA5 cloud cover. The January record high is 73°F (2005) and the record low is -19°F (1984).
Boulder weather in February
In February, Boulder averages a high of 48°F and a low of 23°F. It gets 1.0 in of precipitation over about 7 rainy days. Estimated sunshine is 55% of daylight hours, derived from ERA5 cloud cover. The February record high is 77°F (1982) and the record low is -24°F (1989).
Boulder weather in March
In March, Boulder averages a high of 57°F and a low of 30°F. It gets 2.0 in of precipitation over about 8 rainy days. Estimated sunshine is 50% of daylight hours, derived from ERA5 cloud cover. The March record high is 89°F (2026) and the record low is -6°F (2002).
Boulder weather in April
In April, Boulder averages a high of 63°F and a low of 35°F. It gets 3.0 in of precipitation over about 10 rainy days. Estimated sunshine is 54% of daylight hours, derived from ERA5 cloud cover. The April record high is 88°F (1989) and the record low is -3°F (1975). April is one of the most comfortable months to visit.
Boulder weather in May
In May, Boulder averages a high of 71°F and a low of 43°F. It gets 3.2 in of precipitation over about 13 rainy days. Estimated sunshine is 47% of daylight hours, derived from ERA5 cloud cover. The May record high is 95°F (2000) and the record low is 17°F (2013).
Boulder weather in June
In June, Boulder averages a high of 82°F and a low of 52°F. It gets 1.9 in of precipitation over about 10 rainy days. Estimated sunshine is 52% of daylight hours, derived from ERA5 cloud cover. The June record high is 102°F (2012) and the record low is 33°F (1998).
Boulder weather in July
In July, Boulder averages a high of 88°F and a low of 57°F. It gets 1.8 in of precipitation over about 11 rainy days. Estimated sunshine is 59% of daylight hours, derived from ERA5 cloud cover. The July record high is 102°F (2026) and the record low is 42°F (1972).
Boulder weather in August
In August, Boulder averages a high of 86°F and a low of 56°F. It gets 1.7 in of precipitation over about 11 rainy days. Estimated sunshine is 59% of daylight hours, derived from ERA5 cloud cover. The August record high is 104°F (2026) and the record low is 40°F (2004).
Boulder weather in September
In September, Boulder averages a high of 78°F and a low of 49°F. It gets 2.1 in of precipitation over about 8 rainy days. Estimated sunshine is 69% of daylight hours, derived from ERA5 cloud cover. The September record high is 100°F (1983) and the record low is 15°F (1985). September is one of the most comfortable months to visit.
Boulder weather in October
In October, Boulder averages a high of 66°F and a low of 38°F. It gets 1.6 in of precipitation over about 7 rainy days. Estimated sunshine is 68% of daylight hours, derived from ERA5 cloud cover. The October record high is 89°F (2005) and the record low is 3°F (2019). October is one of the most comfortable months to visit.
Boulder weather in November
In November, Boulder averages a high of 54°F and a low of 29°F. It gets 1.2 in of precipitation over about 6 rainy days. Estimated sunshine is 63% of daylight hours, derived from ERA5 cloud cover. The November record high is 81°F (2025) and the record low is -11°F (2014).
Boulder weather in December
In December, Boulder averages a high of 46°F and a low of 22°F. It gets 0.8 in of precipitation over about 5 rainy days. Estimated sunshine is 59% of daylight hours, derived from ERA5 cloud cover. The December record high is 76°F (1980) and the record low is -24°F (1990).
Sunshine, humidity and wind in Boulder
September is the sunniest month in Boulder, with estimated sunshine of 69% of daylight hours from ERA5 cloud cover. May is the cloudiest, at 47%. The annual cloud-cover estimate is 57% of daylight hours; it is not a measurement of sunshine duration. Boulder is sunnier than 80% of the US.
Humidity peaks in January at 64% and is lowest in September at 44%.
Boulder has about 33 days a year above 90°F. Boulder is hotter than 54% of the US.
Thunderstorms occur on about 40 days a year.
See where Boulder ranks: sunniest cities in the US, cloudiest cities in the US, hottest cities in the US.
First and last freeze in Boulder
The first fall freeze in Boulder typically comes around October 7, and the last spring freeze around May 3. That leaves a frost-free growing season of about 157 days.
Boulder weather records
These records cover BOULDER during 1970–2026. Earlier records or other stations in the city may differ.
The hottest temperature on record at the Boulder station is 104°F, on August 3, 2026. The coldest is -24°F, on February 5, 1989.
The wettest day in the available station history brought 9.1 in of precipitation, on September 12, 2013.
45 all-time records have been set at the station since 1970.
The annual mean temperature has changed by +0.3°F per decade since 1970.
The best time to visit Boulder
The most comfortable time to visit is typically April and September to October, when daytime highs sit near 69°F.
Winter (December–February) is chilly, with average highs around 47°F and lows near 22°F. Snow is possible.
Spring (March–May) is mild, with average highs around 64°F and lows near 36°F.
Summer (June–August) is hot, with average highs around 85°F and lows near 55°F.
Autumn (September–November) is mild, with average highs around 66°F and lows near 38°F.
Monthly climate
| Month | Average low | Average high | Precip | Rain days | Humidity | Estimated sunshine | Record high | Record low |
|---|---|---|---|---|---|---|---|---|
| January | 22° | 47° | 0.83 in | 6 | 64% | 52% | 73° | -19° |
| February | 23° | 48° | 0.99 in | 7 | 60% | 55% | 77° | -24° |
| March | 30° | 57° | 2.0 in | 8 | 59% | 50% | 89° | -6° |
| April | 35° | 63° | 3.0 in | 10 | 51% | 54% | 88° | -3° |
| May | 43° | 71° | 3.2 in | 13 | 56% | 47% | 95° | 17° |
| June | 52° | 82° | 1.9 in | 10 | 52% | 52% | 102° | 33° |
| July | 57° | 88° | 1.8 in | 11 | 49% | 59% | 102° | 42° |
| August | 56° | 86° | 1.7 in | 11 | 48% | 59% | 104° | 40° |
| September | 49° | 78° | 2.1 in | 8 | 44% | 69% | 100° | 15° |
| October | 38° | 66° | 1.6 in | 7 | 46% | 68% | 89° | 3° |
| November | 29° | 54° | 1.2 in | 6 | 52% | 63% | 81° | -11° |
| December | 22° | 46° | 0.81 in | 5 | 54% | 59% | 76° | -24° |
Station: BOULDER, 3 km from the city. Temperature normal baseline: 1991–2020, calculated from available NOAA GHCN-Daily observations. Available station history: 1970–2026; record values refer to this station and period, not the entire city’s history. Precipitation includes rain and the water equivalent of frozen precipitation; snowfall depth is shown separately when available. Sources and methods
From ERA5 reanalysis. Sunshine is estimated from cloud cover.
Boulder climate questions
How much rain does Boulder get?
Boulder gets 21.2 in of precipitation in an average year, over about 101 rainy days.
What is the wettest month in Boulder?
May is the wettest month in Boulder, with 3.2 in. December is the driest, with 0.8 in.
How many rainy days does Boulder have a year?
Boulder has about 101 days with measurable rain in an average year. May has the most, about 13.
Does it snow in Boulder?
Yes. Boulder gets about 92.8 in of snow in an average season. The snowiest winter on record is 2019–20, with 152.0 in.
What is the hottest month in Boulder?
July is the warmest month in Boulder, with an average high of 88°F.
What is the coldest month in Boulder?
January is the coldest month in Boulder, with an average low of 22°F.
What is the record high temperature in Boulder?
Within the available 1970–2026 station history, the record high at the Boulder station is 104°F, set on August 3, 2026. The record low is -24°F, on February 5, 1989.
What is the sunniest month in Boulder?
September is the sunniest month in Boulder, with estimated sunshine of 69% of daylight hours from ERA5 cloud cover. May is the cloudiest.
When is the first frost in Boulder?
The first fall freeze in Boulder typically comes around October 7. The last spring freeze is around May 3.
What is the best time to visit Boulder?
The most comfortable time to visit is typically April and September to October, when daytime highs sit near 69°F.