Knoxville, IA: frost dates by year

Last spring and first fall frost at NOAA station USC00134502, 1951 to 2023, measured from daily minimum temperatures.

Elevation 895 ft, 41.325, -93.101. Download the data (JSON), NOAA daily records

Summary at 32°F

	Last spring frost	First fall frost
Median	Apr 20	Oct 14
Earliest	Mar 24 (1998)	Sep 19 (1991)
Latest	May 15 (1973)	Nov 3 (1973)
Trend	1.2 days earlier per decade	1.1 days later per decade
Years with data	58	59

At 28°F (hard freeze) the median last spring date is Apr 10 and the median first fall date is Oct 26.

The trend is a straight-line fit through the years with a freeze. A positive spring trend means the last frost now comes later. Short or patchy records give noisy trends.

Chart

Last spring frost (32°F)

First fall frost (32°F)

Dots are single years. The gray line is the median, the green line the fitted trend.

Year by year

Year	Last spring 32°F	First fall 32°F	Last spring 28°F	First fall 28°F
2023	Apr 1	no data	Mar 30	no data
2022	Apr 27	Oct 15	Apr 27	Oct 15
2021	Apr 22	Nov 1	Apr 21	Nov 2
2020	no data	Oct 19	no data	Oct 26
2019	Apr 28	Oct 12	Apr 2	Oct 26
2018	Apr 21	Oct 15	Apr 17	Oct 21
2017	Apr 7	Oct 28	Mar 23	Oct 29
2016	Apr 13	Oct 13	Apr 12	Nov 19
2015	Apr 22	Oct 30	Mar 28	Nov 20
2014	Apr 18	Oct 31	Apr 16	Nov 1
2013	May 4	Oct 23	Apr 24	Oct 25
2012	Apr 11	Oct 6	Mar 9	Oct 6
2003	Apr 10	no data	Apr 10	no data
2001	Apr 19	Oct 7	Apr 12	Oct 27
1998	Mar 24	no data	Mar 24	no data
1997	Apr 16	Oct 21	Apr 16	Oct 21
1996	Apr 23	Oct 30	Apr 9	Oct 30
1995	Apr 13	Sep 22	Apr 5	Nov 2
1994	Apr 29	Oct 25	Apr 7	Oct 26
1993	Apr 6	Oct 10	Apr 5	Oct 29
1992	May 6	Oct 17	Apr 12	Oct 17
1991	Apr 10	Sep 19	Mar 30	Oct 19
1990	Apr 17	Oct 18	Apr 17	Oct 25
1989	May 6	Oct 7	Apr 12	Oct 19
1988	Apr 19	Oct 4	Apr 19	Oct 5
1987	Apr 4	Oct 3	Apr 4	Oct 11
1986	Apr 22	Oct 14	Apr 22	Nov 9
1985	Apr 9	Oct 1	Apr 9	Nov 4
1984	no data	Sep 26	no data	Nov 2
1983	Apr 20	Oct 12	Apr 19	Nov 16
1982	Apr 22	Oct 21	Apr 11	Nov 4
1981	Apr 14	Oct 19	Mar 20	Oct 19
1980	May 8	Oct 12	Apr 15	Oct 26
1979	Apr 28	Oct 13	Apr 6	Oct 13
1978	Apr 21	Oct 14	Mar 26	Nov 14
1977	no data	Oct 11	no data	Oct 16
1976	May 3	Oct 6	Mar 22	Oct 6
1975	Apr 20	Oct 2	Apr 12	Oct 29
1974	Apr 15	Sep 22	Apr 8	Oct 2
1973	May 15	Nov 3	Apr 13	Nov 5
1972	Apr 8	Oct 15	Apr 8	Oct 19
1971	no data	Oct 31	no data	Nov 6
1970	May 2	Oct 10	Apr 4	Nov 14
1969	Mar 29	Oct 14	Mar 29	Oct 27
1968	Apr 25	Oct 4	Apr 5	Oct 25
1967	May 3	Sep 29	Apr 24	Oct 11
1966	May 10	Oct 1	May 10	Oct 22
1965	Apr 19	Sep 24	Apr 16	Oct 24
1964	Apr 9	Sep 28	Apr 9	Oct 9
1963	Apr 24	Oct 29	Apr 4	Nov 1
1962	Apr 16	Oct 23	Apr 15	Oct 25
1961	May 2	Oct 20	Apr 16	Nov 3
1960	May 8	Oct 19	Apr 10	Oct 20
1959	Apr 22	Oct 9	Mar 22	Oct 12
1958	May 6	Oct 1	Apr 29	Oct 28
1957	Apr 14	Oct 19	Apr 14	Oct 25
1956	Apr 30	Oct 26	Apr 24	Nov 9
1955	Apr 7	Oct 15	Mar 28	Oct 24
1954	May 4	Oct 18	Apr 4	Oct 30
1953	Apr 20	Oct 27	Apr 20	Oct 27
1952	Apr 16	Oct 6	Apr 11	Oct 6
1951	Apr 23	Sep 28	Apr 23	Oct 31

"none" means the station recorded no freeze at that threshold in that half of the year. "no data" means more than 10% of the season's daily readings were missing. Years with no usable data are left out. See the methodology for the rules, and the ZIP lookup for 1991 to 2020 frost probabilities.