Historical weather data, all-time temperature records, and monthly climate averages for Boulder, CO. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4th in Boulder is a coin-flip kind of day — 130 years of data put the average high at 58° with a 19% chance of snow still lurking. The date's range tells the whole story: it's hit 80° as recently as 2021, and bottomed out at 9° back in 1945.
Boulder's weather has real teeth on both ends. The thermometer has swung from a brutal -33° in January 1930 all the way up to 104° in June 1954 — a 137-degree spread. The wildest single day on record may be September 12, 2013, when 9.08 inches of rain fell, or October 25, 1997, when 22.1 inches of snow buried the city.
Summer is Boulder's sweet spot, peaking the week of July 9–15 with average highs of 87° and reliably sunny skies. If you're chasing the shoulder seasons, spring is the wetter bet — the rainiest stretch runs mid-May with about 0.75 inches per week. Winter stays milder than people expect, with January highs averaging 45°, though cold snaps can be severe.