| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 8.3° | -5.6° | 20.2mm | 5.9 | 39 |
| February | 8.8° | -5.4° | 29mm | 7.2 | 39 |
| March | 13.6° | -1.6° | 50.3mm | 8.1 | 58 |
| April | 17.1° | 1.6° | 78.4mm | 9.7 | 71 |
| May | 21.6° | 6° | 87.8mm | 12.4 | 75 |
| June | 28.1° | 11° | 48.9mm | 10.2 | 75 |
| July | 31.4° | 14.3° | 47.7mm | 10.6 | 61 |
| August | 30.3° | 13.5° | 40.7mm | 9.9 | 67 |
| September | 26.4° | 9.4° | 53.6mm | 7.8 | 84 |
| October | 19.1° | 3.3° | 38mm | 6.7 | 84 |
| November | 13° | -1.5° | 25.3mm | 5.5 | 61 |
| December | 8.3° | -5.5° | 21.8mm | 5.2 | 41 |
January in Boulder averages a daily high of 8.3°C with nights around -5.6°C. Expect roughly 5.9 wet days totalling 20.2mm. Demanding conditions — pack for it and plan indoor options.
February in Boulder averages a daily high of 8.8°C with nights around -5.4°C. Expect roughly 7.2 wet days totalling 29mm. Demanding conditions — pack for it and plan indoor options.
March in Boulder averages a daily high of 13.6°C with nights around -1.6°C. Expect roughly 8.1 wet days totalling 50.3mm. Generally workable, with some weather to plan around.
April in Boulder averages a daily high of 17.1°C with nights around 1.6°C. Expect roughly 9.7 wet days totalling 78.4mm. Generally workable, with some weather to plan around.
May in Boulder averages a daily high of 21.6°C with nights around 6°C. Expect roughly 12.4 wet days totalling 87.8mm. Comfortable conditions for being outdoors all day.
June in Boulder averages a daily high of 28.1°C with nights around 11°C. Expect roughly 10.2 wet days totalling 48.9mm. Comfortable conditions for being outdoors all day.
July in Boulder averages a daily high of 31.4°C with nights around 14.3°C. Expect roughly 10.6 wet days totalling 47.7mm. Generally workable, with some weather to plan around.
August in Boulder averages a daily high of 30.3°C with nights around 13.5°C. Expect roughly 9.9 wet days totalling 40.7mm. Generally workable, with some weather to plan around.
September in Boulder averages a daily high of 26.4°C with nights around 9.4°C. Expect roughly 7.8 wet days totalling 53.6mm. Comfortable conditions for being outdoors all day.
October in Boulder averages a daily high of 19.1°C with nights around 3.3°C. Expect roughly 6.7 wet days totalling 38mm. Comfortable conditions for being outdoors all day.
November in Boulder averages a daily high of 13°C with nights around -1.5°C. Expect roughly 5.5 wet days totalling 25.3mm. Generally workable, with some weather to plan around.
December in Boulder averages a daily high of 8.3°C with nights around -5.5°C. Expect roughly 5.2 wet days totalling 21.8mm. Demanding conditions — pack for it and plan indoor options.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Boulder peaks at 84.
Based on 30 years of records, September–October scores highest for comfort in Boulder, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 31.4°C.
May is the wettest, averaging 87.8mm of rain across roughly 12.4 wet days.
January is the coolest month, with average daily highs around 8.3°C.