In summer the city is warm, even hot, during the day but cool at night, and a jacket is needed most evenings year-round.
Winter days are normally mild but cool off considerably at night.
You may find yourself in shirtsleeves on a February day, but bundling up after dark. Summer is the most popular time for visitors because of pleasant weather and Rockies baseball games, and because Denver is a natural gateway to Rocky Mountain National Park and other popular scenic and sports destinations. Because of Denver's dry climate, hot doesn't mean steamy and cold doesn't mean bone-chilling. In fact, one of the main things visitors need to remember is to drink plenty of water to avoid dehydration. Denver has a reputation for being very cold and snowy in winter, but in fact, snow rarely lingers in the city and arctic cold is also uncommon.