Climate in Boulder, United States

Boulder, United States has a semi-arid climate. The annual average temperature is about 17.8°C, with around 2905 hours of sunshine; the national rainfall baseline is roughly 449 mm across 48 rainy days a year. The warmest month is Jul (highs near 32°C) and the coldest is Jan (lows near 3.5°C). These are deterministic planning estimates, not a forecast or measured station data. Temperature and sunshine follow the city's latitude; rainfall and the climate zone come from a country-level baseline that every city in the country shares (refined by region in the United States, Canada and Australia), so they do not show local differences. Check current conditions with an official meteorological service before travel.

Data year 2025; last updated 2026-05-16.

Boulder is classified as Semi-Arid. The classification combines the city’s own temperature range, which follows its latitude, with a rainfall pattern taken at country level for United States — so cities in the same country usually share a zone.

The rainfall baseline for United States is about 449 mm a year over roughly 48 rainy days, with the wettest month May and the driest Jan. This figure is not specific to Boulder: every city in United States carries the same baseline, so it will not show the difference between, say, a dry inland city and a wet coastal one. Use an official meteorological service for local rainfall.

Boulder sees an estimated 2905 hours of sunshine a year, concentrated in the warmer months around Jul.

By temperature and rainfall, the most comfortable months in Boulder are Apr, Oct, Mar. Conditions vary year to year — verify with a current forecast before booking.

Boulder has a climate comfort score of 81/100, a very comfortable year-round climate by this measure. The score weights mild temperatures most, then rainfall balance, sunshine, low seasonality, and the absence of extreme winter cold or summer heat.

• Climate in Denver — Semi-Arid, comfort 81/100
• Climate in Salt Lake City — Semi-Arid, comfort 81/100
• Climate in Madison — Humid Continental, comfort 72/100