DDZ Bridge over New Fork River · Photo: Clayton B. Fraser · Public domainFew U.S. towns have colder winter nights than Boulder
Midsummer highs settle at about 81°. Its yearly precipitation falls short of 97% of U.S. towns. The latest 30-year average runs 1.4° warmer than 1901–2000’s, with January up the most. Radiators earn their keep from October to May, the months that average under 50°.
A year in Boulder at a glance
Each month’s typical high and low, and what it brings.
What stands out about Boulder’s climate
Compared with towns across the U.S., with Boulder’s place in Wyoming beside it.
What a year in Boulder feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
A freeze is possible in every month
About 258 nights a year fall to 32° or below, and 70 to 0° or below. Frost and day counts come from NOAA’s station at Boulder Rearing Stn, WY, 2.3 miles from the town’s center, at about the same height.
The 2023 USDA map puts Boulder’s center in zone 3b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −30°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 42 inches of snow a winter
Snow, measured at Boulder Rearing Stn, WY, falls mostly in January, February and December. Precipitation (rain plus melted snow) adds up to 10 inches a year; May is the wettest month and November the driest. Rain or snow falls on about 75 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Boulder
Nearly all of the work is heating: a normal year has almost no cooling days. Months averaging under 55° run from September through June.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Boulder Rearing Stn, WY.
Living with Boulder’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
Zone 3b, and frost can come in any month. The longest frost-free stretch in half of years is about 43 days.
Months with highs of 62–84° and lows of 40° or more: July.
Parks & trails →Of the yearly building losses FEMA expects in Boulder from natural hazards, avalanches are the largest share (55%); heat waves, cold waves, winter storms and ice storms together are 2%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Boulder and similar climates
TownRatings has no climate map of the towns around Boulder yet.
Climates most like Boulder’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Boulder, WY | −2° | 81° | 10" | 42" |
| Gunnison, CO | 0° | 82° | 12" | 50" |
| Minot, ND | 2° | 82° | 17" | 52" |
| East Grand Forks, MN | −2° | 81° | 23" | 49" |
| Havre, MT | 6° | 85° | 13" | 41" |
Temperatures and precipitation come from NOAA’s 5 km grid; snow and day counts from the stations named on this page.
Warmer than it used to be
The last 30 years in Boulder averaged 1.4° warmer than the 1900s. The biggest change is in January (+3.3°).
A bigger shift than in 51% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Boulder compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Boulder’s place among Wyoming’s.
Boulder weather by month
Highs, lows and precipitation from NOAA’s grid at Boulder’s center; snow, wet days and snow on the ground from Boulder Rearing Stn, WY. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 29° | −2° | 0.6" | 6.8" | 6 | 31 | 5° – 21° |
| February | 31° | 1° | 0.6" | 7.3" | 6 | 28 | 7° – 26° |
| March | 42° | 13° | 0.6" | 5.3" | 5 | 25 | 18° – 36° |
| April | 52° | 21° | 0.9" | 4.9" | 7 | 6 | 31° – 42° |
| May | 62° | 30° | 1.6" | 1.9" | 9 | 1 | 39° – 51° |
| June | 72° | 37° | 1.2" | 0.2" | 7 | 0 | 49° – 59° |
| July | 81° | 42° | 0.7" | 0.0" | 5 | 0 | 53° – 66° |
| August | 80° | 40° | 0.8" | 0.0" | 6 | 0 | 56° – 63° |
| September | 70° | 32° | 1.1" | 0.3" | 7 | 0 | 48° – 55° |
| October | 56° | 22° | 0.9" | 3.6" | 5 | 2 | 31° – 45° |
| November | 41° | 10° | 0.6" | 4.9" | 5 | 12 | 16° – 32° |
| December | 30° | 0° | 0.6" | 6.9" | 7 | 28 | 7° – 21° |
| Year | 54° | 20° | 10.1" | 42.1" | 75 | 133 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 7° to 26°. August is the most reliable, staying within 7°.
Where Boulder’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Boulder’s center.
- Snow: Boulder Rearing Stn, WY.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Boulder Rearing Stn, WY, 2.3 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Boulder’s climate
What is the weather like in Boulder?
A typical July afternoon reaches 81°, a January night drops to −2°, and about 42 inches of snow falls in a normal winter. Colder January nights than all but 33 U.S. towns; cooler July afternoons than 89% of U.S. towns.
How cold does it get in Boulder in winter?
January nights average −2°. About 258 nights a year reach 32° or below and 70 reach 0° or below. In the coldest January of the last 30 years the month averaged 5°.
How much snow does Boulder get?
About 42 inches in a normal winter at Boulder Rearing Stn, WY, most of it in January, February and December, with snow on the ground about 133 days a year.
How hot does it get in Boulder?
July, with a typical high of 81° and a low of 42°. About 2 days a year reach 90° (Boulder Rearing Stn, WY).
When is the first and last frost in Boulder?
There is no reliable frost-free season: at Boulder Rearing Stn, WY, every month has nights at 32° or below, about 258 a year. In half of years the longest stretch without a freeze is about 43 days.
What growing zone is Boulder in?
Zone 3b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −30°.
What is the best time of year to visit Boulder?
By one simple rule (highs of 62–84° and lows of 40° or more), July. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Boulder getting warmer?
Yes: 1991–2020 averaged 1.4° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 51% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Boulder.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.