In December, Thornton typically sees daytime highs of 8.0°C and overnight lows around -7.0°C. Compared to the annual average high of 18.6°C, December runs -10.6°C.
December in Thornton averages a daytime high of 8.0°C and an overnight low of -7.0°C.
December runs -10.6°C compared to Thornton's annual average high of 18.6°C, ranking #11 of 12 months by warmth.
Plan for daytime highs near 8.0°C and cooler evenings around -7.0°C.