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-present
| earliest day of frost: | Sep 8 (2020) |
| 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: | Sep 8 (2020) |
| latest day: | Oct 31 (1963) |
| average: | Oct 4 |
| first quartile: | Sep 27 |
| median: | Oct 6 |
| third quartile: | Oct 15 |
| standard deviation: | 11.6 days |