Thornton averages 48.8 days a year above 90°F, with May the wettest month at 2.35 in of normal rain. The hottest day on record was 110°F on Aug 2, 2008; the coldest, −24°F on Dec 22, 1990. The single biggest 24-hour rain event recorded was 2.45 in on Aug 24, 1992.
Climate and Average Weather Year Round in Thornton
Year-round temperature
In Thornton, the warmest months are June through September, with average daily highs between 82°F and 91°F. The coldest stretch runs December through February, with highs between 48°F and 50°F and overnight lows reaching 19°F.
Rainfall through the year
Rainfall in Thornton averages 1.2 in per month over the long run. May is the wettest at 2.4 in, while January is the driest at 0.5 in.
Days at 90 °F or hotter
Thornton averages 48.8 days per year at 90 °F or hotter. The hottest year on record saw 88 such days (2024); the coolest just 7 (2026).
Precipitation this year
As of May 28, Thornton has received 5.0 in of precipitation this year — 20% below the long-term normal for this point in the year (6.3 in).