Climate averages 1991–2020
Boulder weather
in January.
A cold, fairly dry month: the 11th warmest and the 2nd driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
January is a cold month in Boulder: daytime highs average 4.2°C and nights cool to about -8.7°C. By daytime temperature it is the 11th warmest of the 12 months.
Expect about 24 mm of rain on roughly 6 days, which makes January a fairly dry month (the 2nd driest of the 12 months). Daylight, from sunrise to sunset, lasts about 9 h 41 min on an average January day.
The nearest other city in this atlas is Longmont (22 km away). In January its highs average 4.5°C, about as warm as Boulder, with 19 mm of rain.
Among the 498 cities listed in the United States, Boulder ranks joint 342nd of 498 for the warmest January highs and joint 37th of 498 for the driest January (rainfall, lowest first). The mean January high of those 498 cities is 9.5°C; Boulder is 5.2°C cooler than that mean.
From January to February, average highs rise by 1.1°C to 5.4°C, and monthly rainfall rises from 24 mm to 26 mm.
The annual picture
January in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Boulder climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January, selected | 4.2°C-8.7°C | -8.7°C | 24 | 5.7 | 9.710 h |
| February | 5.4°C-8.3°C | -8.3°C | 26 | 6.7 | 10.711 h |
| March | 10.0°C-4.5°C | -4.5°C | 50 | 8.8 | 11.912 h |
| April | 13.7°C-0.4°C | -0.4°C | 78 | 11.1 | 13.213 h |
| May | 19.2°C5.1°C | 5.1°C | 103 | 14.9 | 14.414 h |
| June | 25.6°C10.8°C | 10.8°C | 77 | 14.2 | 15.015 h |
| July | 28.7°C14.4°C | 14.4°C | 75 | 14.8 | 14.715 h |
| August | 27.5°C13.7°C | 13.7°C | 71 | 14.8 | 13.814 h |
| September | 23.7°C9.5°C | 9.5°C | 54 | 9.6 | 12.512 h |
| October | 16.5°C3.1°C | 3.1°C | 48 | 7.4 | 11.211 h |
| November | 9.1°C-3.9°C | -3.9°C | 32 | 6.4 | 10.010 h |
| December | 4.0°C-8.8°C | -8.8°C | 23 | 5.3 | 9.49 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
January in nearby cities
- Longmont in JanuaryUnited States · 22 kmHigh 4.5°C · Low -8.4°C · 19 mm rain
- Westminster (Colorado), United States in JanuaryUnited States · 28 kmHigh 4.6°C · Low -9.6°C · 22 mm rain
- Arvada in JanuaryUnited States · 28 kmHigh 4.7°C · Low -9.7°C · 22 mm rain
- Thornton in JanuaryUnited States · 30 kmHigh 4.3°C · Low -9.7°C · 22 mm rain
- Lakewood in JanuaryUnited States · 38 kmHigh 4.7°C · Low -9.0°C · 22 mm rain
- Denver in JanuaryUnited States · 39 kmHigh 4.8°C · Low -9.4°C · 22 mm rain
- Loveland in JanuaryUnited States · 46 kmHigh 4.5°C · Low -8.9°C · 16 mm rain
- Aurora (Colorado), United States in JanuaryUnited States · 49 kmHigh 5.4°C · Low -7.9°C · 14 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Boulder) is explained once on the Boulder year overview and on the Sources, method and limits page.