Historical weather data, all-time temperature records, and monthly climate averages for Johnstown, CO. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 5 in Johnstown runs warm for early spring, with an average high of 61° and a low of 29°—a wide swing that's classic Colorado Front Range. There's a 42% chance of precipitation today historically, and a 15% shot at snow, so don't put the scraper away just yet. The date has seen everything from 80° in 1991 to an 18° overnight low as recently as 2023.
Johnstown's weather has genuine teeth on both ends: the thermometer has hit 106° in July and plunged to -31° in December, a 137-degree spread over the record period. A single storm dropped 20 inches of snow on December 21, 2006, and the wettest day on record dumped 2.62 inches of rain back in June 1994.
Summer is the clear sweet spot, with highs peaking around 88-89° during the second week of July, while January stays cold and dry with highs only reaching the low 40s. If rain is a concern, late spring is the time to watch—the wettest week of the year typically falls in mid-May, averaging 0.77 inches. The shoulder months of April and October offer mild highs in the 60s, though temperature swings of 30+ degrees in a single day are always on the table.