Historical weather data, all-time temperature records, and monthly climate averages for Longmont, CO. Explore typical weather conditions by week for trip planning, and see how today compares to the historical record.
April 4th in Longmont is a classic shoulder-season day, with average highs of 58° and lows dipping to a chilly 28°. The date's range tells the whole story — it's hit as warm as 81° back in 2021 and as cold as 13° in 1918. There's a 1-in-10 chance of snow today, so don't put the jacket away just yet.
Longmont's weather has real teeth at both ends of the thermometer — 106° in June 1994 and a brutal -38° in January 1930 represent a swing of 144 degrees across its recorded history. The snowiest single day on record was a staggering 37 inches on April 18, 1920, a reminder that Colorado's wildest snow events often come in spring, not winter.
Longmont peaks in early July with average highs of 89°, while January is the coldest stretch at just 42°. If you're trying to dodge rain, aim for fall or winter — the wettest stretch of the year is mid-May, averaging 0.63 inches in a single week. Spring and early summer bring the most weather drama; the rest of the year is reliably mild.