Boulder gets bright, sunny days (more than 300 a year) with immediate access to the cool high country in its backyard.
In general, Boulder has a warm, dry, mild climate—with the exception of a few weeks of extreme heat in the summer and a few weeks of extreme cold and snow in the winter. A record-breaking 90 F/32 C day in the spring can be followed by a snow storm the next day.
Be prepared for rain and cold at any moment, and you'll be fine. Also, don't be surprised by sudden, gusty winds.