First Day of Frost in Boulder

Data from 1957-1995

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).

earliest day of frost: Sep 12 (1974) latest day: Oct 31 (1963) average: Oct 6 first quartile Sep 25 median Oct 5 third quartile Oct 18 standard deviation 13.6 days