Last Day of Spring 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).

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Data from 1948-2025

earliest day of last frost:  Apr   3 (2012)
latest day:                  Jun   3 (1951)

average:                     May 5

low quartile                 April 28
median                       May 3
high quartile                May 14

standard deviation           11.6 days
skewness                      0.06
kurtosis                     -0.13

1948 04 25
1949 05 07
1950 05 27
1951 06 04
1952 04 21
1953 05 14
1954 05 04
1955 05 29
1956 04 09
1957 05 18
1958 05 01
1959 04 22
1960 05 18
1961 04 28
1962 04 13
1963 04 24
1964 04 17
1965 05 10
1966 05 14
1967 05 15
1968 05 16
1969 04 29
1970 05 02
1971 04 28
1972 05 01
1973 05 04
1974 05 01
1975 05 02
1976 04 30
1977 04 22
1978 05 08
1979 missing
1980 04 24
1981 05 11
1982 05 07
1983 05 15
1984 04 29
1985 05 15
1986 04 20
1987 04 22
1988 05 02
1989 05 02
1990 05 11
1991 05 04
1992 04 24
1993 05 03
1994 05 05
1995 05 25
1996 04 28
1997 05 04
1998 04 30
1999 05 18
2000 05 16
2001 05 22
2002 05 25
2003 05 12
2004 04 30
2005 05 04
2006 05 12
2007 05 07
2008 05 10
2009 04 28
2010 05 14
2011 05 06
2012 04 03
2013 05 06
2014 05 15
2015 05 12
2016 05 01
2017 05 21
2018 04 26
2019 05 23
2020 04 17
2021 04 25
2022 05 23
2023 04 29
2024 04 26
2025 04 21