Climateby Month

Boulder, CO climate by month

NOAA 1991-2020 normals · 5,319 ft elevation · also covers Longmont

Boulder has hot summers and chilly and snowy winters. Highs peak at 88°F in July and fall to 46°F in December. The wettest month is May (about 13 wet days) and the driest is December (about 5). Normal snowfall is about 93 in a year. By our comfort score the best month is May.

Warmest month
88°F
July normal high
Coldest month
21°F
December normal low
Wet days a year
101
21.2 in of precipitation
Snow a year
92.8 in
normal snowfall

How warm is Boulder?

Normal highs range from 46°F in December to 88°F in July.

20°40°60°80°100° January: normal high 47°F (8°C), low 22°F (-6°C) February: normal high 48°F (9°C), low 22°F (-6°C) March: normal high 57°F (14°C), low 29°F (-2°C) April: normal high 63°F (17°C), low 35°F (2°C) May: normal high 71°F (22°C), low 43°F (6°C) June: normal high 83°F (28°C), low 51°F (11°C) July: normal high 88°F (31°C), low 57°F (14°C) 88° 57° August: normal high 86°F (30°C), low 56°F (13°C) September: normal high 79°F (26°C), low 48°F (9°C) October: normal high 66°F (19°C), low 37°F (3°C) November: normal high 55°F (13°C), low 28°F (-2°C) December: normal high 46°F (8°C), low 21°F (-6°C) 46° 21° JFMAMJJASOND

Bars run from the normal low to the normal high for each month.

How rainy is Boulder?

May has the most wet days (about 13); the year brings about 21 in of precipitation.

January: 6 wet days February: 7 wet days March: 8 wet days April: 10 wet days May: 13 wet days 13 June: 10 wet days July: 11 wet days August: 11 wet days September: 8 wet days October: 7 wet days November: 6 wet days December: 5 wet days 5 JFMAMJJASOND

Wet day: at least 0.01 in of rain or melted snow, counted from daily records 1991-2020.

How much does it snow?

Normal snowfall is 92.8 in a year, most of it in March.

January: 11.3 in of snow February: 15.0 in of snow March: 15.7 in of snow 15.7 April: 14.7 in of snow May: 2.0 in of snow June: 0.0 in of snow 0.0 July: 0.0 in of snow August: 0.0 in of snow September: 1.0 in of snow October: 7.0 in of snow November: 13.1 in of snow December: 13.0 in of snow JFMAMJJASOND

How humid is Boulder?

Muggy days (dew point 65°F or higher) are rare in any month.

January: 0 muggy days 0 February: 0 muggy days March: 0 muggy days April: 0 muggy days May: 0 muggy days June: 0 muggy days July: 0 muggy days August: 0 muggy days September: 0 muggy days October: 0 muggy days November: 0 muggy days December: 0 muggy days JFMAMJJASOND

Muggy day: daily mean dew point of 65°F or higher, from hourly observations 1991-2020 at Denver International Airport, 35 mi ESE of the city center (the nearest airport with complete hourly records).

How much daylight?

Daylight ranges from about 9.4 hours in December to 15.0 hours in June.

January: 9.7 hours of daylight February: 10.7 hours of daylight March: 12.0 hours of daylight April: 13.3 hours of daylight May: 14.4 hours of daylight June: 15.0 hours of daylight 15.0 July: 14.7 hours of daylight August: 13.7 hours of daylight September: 12.4 hours of daylight October: 11.1 hours of daylight November: 10.0 hours of daylight December: 9.4 hours of daylight 9.4 JFMAMJJASOND
See all numbers
Monthly climate normals and day counts for Boulder, 1991-2020
MonthHighLowPrecip.Wet daysSnowMuggy daysDaylight
January 47°F22°F 0.8 in6 11.3 in 0 9.7 h
February 48°F22°F 1.0 in7 15.0 in 0 10.7 h
March 57°F29°F 2.0 in8 15.7 in 0 12.0 h
April 63°F35°F 3.0 in10 14.7 in 0 13.3 h
May 71°F43°F 3.2 in13 2.0 in 0 14.4 h
June 83°F51°F 1.9 in10 0.0 in 0 15.0 h
July 88°F57°F 1.8 in11 0.0 in 0 14.7 h
August 86°F56°F 1.7 in11 0.0 in 0 13.7 h
September 79°F48°F 2.1 in8 1.0 in 0 12.4 h
October 66°F37°F 1.6 in7 7.0 in 0 11.1 h
November 55°F28°F 1.2 in6 13.1 in 0 10.0 h
December 46°F21°F 0.8 in5 13.0 in 0 9.4 h

High and low: NOAA 1991-2020 normal daily high and low. Wet days: at least 0.01 in of rain or melted snow. Muggy days: daily mean dew point 65°F or higher.

Best months to visit Boulder

By our comfort score, the best month is May.

Comfort score by month (0-100) and its parts, in days per month
MonthScoreComfortableNotable rainHot or cold
Jan 42138
Feb 44247
Mar 59943
Apr 691461
May 761871
Jun 661056
Jul 503414
Aug 545410
Sep 661343
Oct 661641
Nov 52834
Dec 40139

Score = 40 × share of comfortable days + 25 × share of days without notable rain + 20 × share of days neither hot (90°F+) nor cold (high 40°F or below) + 15 × daylight. How the score works.

Frost dates in Boulder

The last spring frost typically comes around May 6, and the first fall frost around Oct 5, leaving 151 frost-free days in a typical year.

Frost and freeze dates for Boulder
Typical date1 year in 10
Last spring frost (32°F)May 6after May 18
First fall frost (32°F)Oct 5before Sep 21
Last hard freeze (28°F)Apr 27after May 10
First hard freeze (28°F)Oct 15before Sep 30
Frost-free season151 daysunder 131 days

"Typical" is the date with a 50% chance of a later spring frost (or earlier fall frost). Planting after the "1 year in 10" spring date gives a 90% chance of no further frost. The Old Farmer's Almanac publishes 30% dates, which fall between our typical and 1-in-10 dates.

Station: Boulder (USC00050848), NOAA 1991-2020 freeze probabilities. Frost dates for every city in Colorado.

Hottest and coldest readings, 1991-2020

The highest reading was 102°F (June 23, 2012); the lowest was -17°F (February 2, 2011).

From the temperature station's daily records with NOAA quality flags removed. Not an all-time record.

Near Boulder

Similar climates elsewhere

Also covers

Longmont uses the same temperature and rain stations as Boulder, so its monthly numbers are the ones on this page.

Where the numbers come from

  • Temperature, rain, snowfall, snow depth and frost dates: Boulder (USC00050848), 1.6 mi S of the city center, 5,484 ft (165 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Humidity and wind by hour: Denver Intl Airport (USW00003017), 35 mi ESE of the city center, 5,414 ft (95 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Cloud cover: Aurora Buckley Fld ANGB (USW00023036), 35 mi SE of the city center, 5,663 ft (344 ft higher than the city). NOAA normals and daily records, 1991-2020.
  • Daily humidity and wind: Denver International Airport (725650-03017), 35 mi ESE of the city center, 5,404 ft (85 ft higher than the city). Hourly observations, 1991-2020.

Distances from the city center (USGS). Methodology · Report an error