The wettest month of the year in Boulder County and the Front Range is May, with a bit over three inches of average precipitation.
The driest month is January, with about ½ inch.
On average, the hottest day of the year in Boulder is July 13th, with an average high of 87° F.
The coldest average high temperature is on January 1st, at 41° F. (Source: noaa.gov)