Grafton Wwtp, WI: frost dates by year

Last spring and first fall frost at NOAA station USC00473198, 2009 to 2025, measured from daily minimum temperatures.

Elevation 741 ft, 43.308, -87.955. Download the data (JSON), NOAA daily records

Summary at 32°F

	Last spring frost	First fall frost
Median	Apr 25	Oct 22
Earliest	Apr 1 (2017)	Oct 3 (2020)
Latest	May 13 (2013)	Nov 12 (2016)
Trend	2.0 days later per decade	5.7 days later per decade
Years with data	14	17

At 28°F (hard freeze) the median last spring date is Apr 8 and the median first fall date is Nov 7.

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
2025	Apr 16	Nov 2	Apr 9	Nov 3
2024	Apr 26	Nov 2	Mar 30	Nov 26
2023	Apr 27	Oct 30	Apr 7	Oct 31
2022	Apr 28	Oct 19	Apr 27	Nov 13
2021	Apr 22	Nov 2	Apr 3	Nov 3
2020	May 10	Oct 3	Apr 17	Oct 25
2019	Apr 28	Oct 25	Apr 3	Nov 1
2018	Apr 29	Oct 13	Apr 19	Nov 10
2017	Apr 1	Nov 1	Mar 23	Nov 8
2016	Apr 12	Nov 12	Apr 10	Nov 20
2015	Apr 24	Oct 17	Apr 4	Nov 14
2014	no data	Oct 19	no data	Nov 2
2013	May 13	Oct 20	Apr 21	Nov 7
2012	no data	Oct 8	no data	Nov 12
2011	Apr 18	Nov 11	Apr 4	Nov 17
2010	Apr 18	Oct 22	Apr 9	Oct 29
2009	no data	Oct 10	no data	Oct 11

"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.