Boulder, Colorado climate: Normal weather by month, frost dates and records
Boulder's normal year runs from 21°F December nights to 88°F July afternoons, with 21.2 inches of precipitation and 93 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 10.8°C, December lows of −6°C, July highs of 31°C, 539 mm of precipitation a year.
- NOAA stationBoulder
- Station IDUSC00050848
- Location39.99°N 105.27°W
- Elevation5,484 ft (1,672 m)
- From the center2 miles
- Population106,803
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Boulder.
- Jan 47° 22°
- Feb 48° 22°
- Mar 57° 29°
- Apr 63° 35°
- May 71° 43°
- Jun 83° 51°
- Jul 88° 57°
- Aug 86° 56°
- Sep 79° 48°
- Oct 66° 37°
- Nov 55° 28°
- Dec 46° 21°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Boulder each month?
July is the warmest month, with normal highs of 88°F; December the coldest, with normal lows of 21°F. The most precipitation falls in May (3.21 in), the least in December (0.81 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 47°F | 22°F | 34.3°F | 0.83 | 11.3 | 6 | <1 | 27 | 9 h 40 min |
| February | 48°F | 22°F | 35.3°F | 0.99 | 15.0 | 7 | <1 | 23 | 10 h 40 min |
| March | 57°F | 29°F | 43.0°F | 1.99 | 15.7 | 8 | <1 | 20 | 11 h 50 min |
| April | 63°F | 35°F | 48.7°F | 3.05 | 14.7 | 10 | <1 | 11 | 13 h 10 min |
| May | 71°F | 43°F | 57.0°F | 3.21 | 2.0 | 13 | 1 | 2 | 14 h 20 min |
| June | 83°F | 51°F | 66.8°F | 1.95 | 0.0 | 10 | 6 | <1 | 15 h |
| July | 88°F | 57°F | 72.5°F | 1.83 | 0.0 | 11 | 14 | <1 | 14 h 50 min |
| August | 86°F | 56°F | 70.7°F | 1.68 | 0.0 | 11 | 10 | <1 | 13 h 50 min |
| September | 79°F | 48°F | 63.5°F | 2.09 | 1.0 | 8 | 3 | 1 | 12 h 30 min |
| October | 66°F | 37°F | 51.6°F | 1.62 | 7.0 | 7 | <1 | 8 | 11 h 10 min |
| November | 55°F | 28°F | 41.3°F | 1.18 | 13.1 | 6 | <1 | 20 | 10 h |
| December | 46°F | 21°F | 33.7°F | 0.81 | 13.0 | 5 | <1 | 27 | 9 h 20 min |
| Year (annual) | 66°F | 37°F | 51.5°F | 21.23 | 92.8 | 101 | 33 | 138 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 8°C | −6°C | 1.3°C | 21 mm | 29 cm |
| February | 9°C | −5°C | 1.8°C | 25 mm | 38 cm |
| March | 14°C | −2°C | 6.1°C | 51 mm | 40 cm |
| April | 17°C | 1°C | 9.3°C | 77 mm | 37 cm |
| May | 22°C | 6°C | 13.9°C | 82 mm | 5 cm |
| June | 28°C | 11°C | 19.3°C | 50 mm | 0 cm |
| July | 31°C | 14°C | 22.5°C | 46 mm | 0 cm |
| August | 30°C | 13°C | 21.5°C | 43 mm | 0 cm |
| September | 26°C | 9°C | 17.5°C | 53 mm | 3 cm |
| October | 19°C | 3°C | 10.9°C | 41 mm | 18 cm |
| November | 13°C | −2°C | 5.2°C | 30 mm | 33 cm |
| December | 8°C | −6°C | 0.9°C | 21 mm | 33 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00050848; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Boulder?
Normal highs sit between 65°F and 85°F in May, June, September and October. Of those, October has the fewest days with rain (7).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00050848.
When is the last frost in Boulder?
In Boulder, the last spring frost (32°F) comes after May 6 in half of years and after May 18 in one year in ten; the first autumn frost comes before October 5 in half of years and before September 21 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- May 61 year in 10 after May 18; 9 in 10 after April 24
- First autumn frost, half of years before
- October 51 year in 10 before September 21; 9 in 10 before October 18
NOAA puts the median frost-free season at 151 days, and the season without a hard freeze (28°F) at 171 days.
A hard freeze (28°F) comes after April 27 in half of springs and before October 15 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Boulder in zone 6a across its 5 ZIP code areas (6a in 80301, the largest).
Frost dates for every NOAA station in Colorado · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00050848; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
What hardiness zone is each Boulder ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Boulder's 5 ZIP code areas are all in zone 6a. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Boulder?
In a normal year in Boulder, 33 days a year reach 90°F (1 of them 100°F or more), 138 nights fall to 32°F or colder and 101 days bring measurable precipitation.
- Days at 90°F or more
- 33a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 138a normal year
- Days that stay below freezing
- 13high of 32°F or less
- Days with 0.01 inch of precipitation
- 101a normal year
- Days with 1 inch of snow or more
- 22a normal year
The highest temperature in this station's record (since 1893) is 104°F, on June 23, 1954; the lowest is −33°F, on January 17, 1930.
The wettest calendar year on that record is 2013, with 34.15 in; the snowiest season is 2019–20, with 152.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00050848; records: ACIS (NOAA Regional Climate Centers), station USC00050848. Records use complete months only; a month missing more than three days is left out.
How sunny is Boulder?
Over a year 77% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Boulder, 4.7 kWh per square metre a day. February is the sunniest month (82%) and May the cloudiest (71%). Among the 459 U.S. places of 50,000 or more, that ranks tied 243rd (with 32 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 81% | 2.7 |
| February | 82% | 3.8 |
| March | 79% | 4.9 |
| April | 73% | 5.6 |
| May | 71% | 6.2 |
| June | 78% | 7.0 |
| July | 75% | 6.4 |
| August | 75% | 5.8 |
| September | 81% | 5.2 |
| October | 80% | 3.9 |
| November | 79% | 2.8 |
| December | 79% | 2.4 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Boulder need?
A normal year in Boulder brings 5,511 heating degree days, 3% more than the median U.S. place (5,373), and 625 cooling degree days, 31% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,812 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 953 | 0 |
| February | 832 | 0 |
| March | 682 | 0 |
| April | 491 | 1 |
| May | 265 | 17 |
| June | 56 | 110 |
| July | 6 | 238 |
| August | 12 | 190 |
| September | 112 | 65 |
| October | 421 | 5 |
| November | 711 | 0 |
| December | 970 | 0 |
| Year (annual) | 5,511 | 625 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00050848. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Boulder been warmer than normal lately?
2025 averaged 53.3°F, 1.8°F above the 1991-2020 normal of 51.5°F. 3 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 52.4°F | +0.9°F | 20.68 | 77.6 |
| 2022 | 51.4°F | −0.1°F | 18.79 | 123.1 |
| 2023 | 51.2°F | −0.3°F | 22.90 | 65.2 |
| 2024 | 53.5°F | +2.0°F | 19.13 | 90.1 |
| 2025 | 53.3°F | +1.8°F | 18.81 | 60.4 |
Source: observed years: ACIS, station USC00050848. A year counts only with all twelve months complete.
How does Boulder's climate compare?
Boulder is warmer than 101 of the other 124 places with their own NOAA record in Colorado, and wetter than 110. Across the 7,247 U.S. stations with normals, its annual mean of 51.5°F is warmer than 47%.
In the Köppen classification computed from these normals, Boulder is Cfa: temperate, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Boulder share this climate record?
14 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Louisville, CO20,811 people · 7 mi E
- Superior, CO13,654 people · 7 mi SE
- Gunbarrel, CO10,424 people · 7 mi NE
- Lazy Acres, CO1,056 people · 7 mi NW
- Paragon Estates, CO767 people · 4 mi E
- Altona, CO532 people · 9 mi N
- Pine Brook Hill, CO497 people · 4 mi NW
- Tall Timber, CO376 people · 5 mi W
- Eldorado Springs, CO355 people · 4 mi S
- Crisman, CO253 people · 7 mi NW
- Sunshine, CO240 people · 7 mi NW
- Glendale, CO71 people · 9 mi NW
- Valmont, CO68 people · 4 mi NE
- Seven Hills, CO44 people · 4 mi NW
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Boulder's other NOAA stations record?
One more NOAA station keeps 1991-2020 normals in or near Boulder. This page uses Boulder; the other differs by site and elevation:
| Station | From the center | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Boulder (14 mi W) USW00094075 | 15 mi W | 9,828 ft | 35.2°F | 12°F | 68°F | 33.9 | – | June 21 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Boulder's climate
What is the coldest month in Boulder?
December, with a normal high of 46°F and a normal low of 21°F. The warmest is July (88°F by day, 57°F at night).
Does it snow in Boulder?
Yes: 93 inches in a normal year, falling on 37 days with 0.1 inch or more, the most in March (15.7 inches).
What is the rainiest month in Boulder?
May, with 3.21 in of precipitation in a normal year; the driest is December with 0.81 in.
What plant hardiness zone is Boulder in?
The USDA's 2023 map puts Boulder in zone 6a across its 5 ZIP code areas (6a in 80301, the largest).
How late can frost come in Boulder?
In half of years the last 32°F night comes after May 6; in one year in ten it comes after May 18. Waiting until May 18 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Colorado climateThe statewide normals and every place in the state
- Gross Reservoir, CO6 miles from this station, 43.9°F a year
- Coal Creek, CO9 miles from this station, 39.9°F a year
- Ralston Reservoir, CO11 miles from this station, 51.5°F a year
- Northglenn, CO15 miles from this station, 52.4°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made