First Day of "Frost" in Boulder

Frost is defined here as the minimum temperature being less than or equal to 32 F. Frost may occur even when the official temperature is above 32F as the ground can be colder than where the thermometer is located (typically 3 meters above the surface).


Data from 1948-2018

earliest day of frost: Sep 13 (1974,2014)
latest day: Oct 31 (1963)
average: Oct 6
first quartile: Sep 27
median: Oct 6
third quartile: Oct 15
standard deviation: 12.3 days

Data from 1897-2018

earliest day of frost: 09/13 (1974,2014)
latest day: Oct 31 (1963)
average: Oct 4
first quartile: Sep 27
median: Oct 6
third quartile: Oct 15
standard deviation: 11.6 days