Historical weather data, all-time temperature records, and monthly climate averages for Thornton, CO. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4 in Thornton sits right in that classic Front Range shoulder season — expect a high around 61° but don't put away the heavy coat just yet, with lows averaging 30°. There's an 18% chance of snow on any given April 4th, a reminder that the Rockies aren't done with winter. The date's wild range tells the full story: 79° in 2005, 14° in 1985.
Thornton's weather has serious range — from a scorching 110° on August 2, 2008, to a brutal -24° on December 22, 1990, that's a 134-degree spread in the historical record. Single-day extremes round out the picture: 2.45 inches of rain on August 24, 1992, and a massive 21.8 inches of snow on December 21, 2006.
Summer is the clear winner for warmth, with the week of July 9–15 averaging a high of 91° — perfect if you can handle Colorado sun. Cool down fast by January, when highs sit around 45° to start the new year. If you're rain-averse, note that late April is the wettest stretch of the calendar, peaking around the 23rd–29th.