Frost Odds at the Madison Airport
NOAA's 1991-2020 climate normals give the chance of a freeze before or after each date.(NOAA normals) Read the spring rows as "the last frost comes after this date": a 90% chance after April 16, 50% after May 1, 10% after May 16. Fall rows read "the first frost comes by this date."
| 1 year in 10 | Median (5 in 10) | 9 years in 10 | |
|---|---|---|---|
| Last spring frost (32°F) | after May 16 | May 1 | after April 16 |
| Last hard freeze (28°F) | after May 5 | April 20 | after April 5 |
| First fall frost (32°F) | by Sept 26 | Oct 10 | by Oct 24 |
| First hard freeze (28°F) | by Oct 6 | Oct 22 | by Nov 4 |
The median frost-free season (32°F) is 160 days, and at least 140 days nine years in 10.(NOAA normals) NOAA also publishes dates for 36°F: the median last 36°F night is May 13, with a 1-in-10 chance after May 29.(NOAA normals) The lawn and yard calendar turns these dates into a month-by-month plan.
What We Found in 86 Years of Airport Data
- May 3Median last 32°F night, 1991-2020 (our count)
- Oct 6Median first 32°F night, 1991-2020
- June 10, 1972Latest spring frost since 1940
- Sept 12, 1955Earliest fall frost since 1940
- Counting actual nights gives slightly different dates than NOAA. The middle of the 30 actual last-frost dates from 1991 to 2020 is May 3, and of first-frost dates Oct 6. NOAA's normals (May 1 and Oct. 10) come from a statistical fit, so use NOAA's for planning and ours to see real years.(NOAA ACIS)
- Fall frost is coming later. The median first fall frost was Oct 1 in 1940-1979 and Oct 10 in 2000-2025. In the last 10 complete years (2016-2025) it was Oct 20.
- Late spring frosts happen. In 19 of 86 years the last frost came on or after May 16. The latest was June 10, 1972; the earliest last frost was April 7, 1955.
- The frost-free season has run from 106 days (1964) to 185 days (1943). The latest first fall frost was Nov 9, 2016.
- 2026 so far: the last spring frost was May 7, and the airport hadn't dropped to 32°F as of Oct 9.
Recent Years
| Year | Last spring frost | First fall frost | Days between |
|---|---|---|---|
| 2026 | May 7 | not yet (through Oct 9) | |
| 2025 | May 9 | Oct 23 | 166 |
| 2024 | April 25 | Oct 16 | 173 |
| 2023 | April 26 | Oct 17 | 173 |
| 2022 | May 4 | Oct 15 | 163 |
| 2021 | May 11 | Oct 22 | 163 |
| 2020 | May 13 | Oct 2 | 141 |
| 2019 | April 28 | Oct 24 | 178 |
| 2018 | April 29 | Oct 12 | 165 |
| 2017 | May 3 | Oct 29 | 178 |
| 2016 | May 15 | Nov 9 | 177 |
| 2015 | April 28 | Oct 16 | 170 |
| 2014 | April 23 | Oct 11 | 170 |
| 2013 | May 13 | Oct 14 | 153 |
| 2012 | April 27 | Sept 24 | 149 |
Frost Depth and Footings
Frost dates tell you about plants. For anything you build, what matters is how deep the ground freezes.
- Footings for a house: Wisconsin's Uniform Dwelling Code says footings for new one- and two-family homes go below the frost penetration level or at least 48 inches below the ground next to them, whichever is deeper.(SPS 321.16) Footings directly under window areaways are an exception if the rest of the foundation is protected.(SPS 321.16)
- Decks, additions and garages: ask your town's building inspector what footing depth applies when you apply for the permit. See remodel permits by town and call Diggers Hotline before you dig.
- Frozen ground for lawn rules: Wisconsin bans fertilizer on frozen turf, and DATCP calls ground frozen when you can't dig down 6 to 8 inches. Snow cover isn't a reliable sign.(DATCP)
- Frost heave: HUD's rehab inspection guide lists frost heave among the causes of foundation settlement and cracking.(HUD) Older basements covers what cracks mean.
Every Year Since 1940
Complete years at the Madison airport. Tap a heading to sort.
| Year | Last 32°F | First 32°F | Days between | Last 28°F | First 28°F |
|---|---|---|---|---|---|
| 1940 | May 4 | Sept 26 | 144 | May 4 | Nov 6 |
| 1941 | April 25 | Oct 27 | 184 | March 30 | Oct 28 |
| 1942 | April 13 | Sept 24 | 163 | April 11 | Sept 28 |
| 1943 | May 1 | Nov 3 | 185 | April 15 | Nov 3 |
| 1944 | April 19 | Oct 22 | 185 | April 5 | Nov 6 |
| 1945 | May 9 | Oct 9 | 152 | April 19 | Nov 3 |
| 1946 | April 27 | Oct 13 | 168 | April 16 | Nov 16 |
| 1947 | May 10 | Oct 1 | 143 | May 9 | Nov 8 |
| 1948 | May 8 | Oct 3 | 147 | April 17 | Oct 17 |
| 1949 | May 10 | Sept 24 | 136 | April 16 | Sept 29 |
| 1950 | May 8 | Sept 24 | 138 | April 21 | Nov 2 |
| 1951 | April 26 | Sept 29 | 155 | April 20 | Oct 31 |
| 1952 | April 16 | Oct 2 | 168 | April 11 | Oct 3 |
| 1953 | April 27 | Oct 7 | 162 | April 20 | Oct 7 |
| 1954 | May 20 | Oct 19 | 151 | May 7 | Oct 19 |
| 1955 | April 7 | Sept 12 | 157 | March 29 | Oct 22 |
| 1956 | May 8 | Sept 19 | 133 | April 30 | Sept 20 |
| 1957 | May 16 | Sept 28 | 134 | April 15 | Sept 28 |
| 1958 | May 23 | Oct 1 | 130 | May 23 | Nov 2 |
| 1959 | April 21 | Oct 17 | 178 | April 21 | Oct 28 |
| 1960 | May 12 | Oct 18 | 158 | May 12 | Oct 20 |
| 1961 | May 26 | Sept 28 | 124 | May 2 | Oct 2 |
| 1962 | April 20 | Sept 20 | 152 | April 20 | Oct 23 |
| 1963 | May 23 | Sept 14 | 113 | May 1 | Oct 29 |
| 1964 | May 29 | Sept 13 | 106 | April 15 | Sept 28 |
| 1965 | May 30 | Sept 26 | 118 | April 27 | Oct 5 |
| 1966 | May 31 | Sept 25 | 116 | May 10 | Sept 26 |
| 1967 | May 22 | Sept 28 | 128 | May 22 | Sept 29 |
| 1968 | May 6 | Oct 4 | 150 | April 27 | Oct 24 |
| 1969 | May 12 | Sept 28 | 138 | April 29 | Oct 15 |
| 1970 | May 6 | Oct 4 | 150 | May 6 | Oct 15 |
| 1971 | May 27 | Oct 7 | 132 | May 3 | Oct 7 |
| 1972 | June 10 | Sept 30 | 111 | April 26 | Oct 15 |
| 1973 | May 4 | Oct 17 | 165 | April 13 | Oct 17 |
| 1974 | May 13 | Sept 22 | 131 | May 7 | Sept 22 |
| 1975 | April 26 | Sept 26 | 152 | April 21 | Sept 26 |
| 1976 | May 18 | Sept 22 | 126 | May 7 | Sept 22 |
| 1977 | May 10 | Oct 3 | 145 | May 10 | Oct 13 |
| 1978 | May 6 | Oct 7 | 153 | May 6 | Oct 7 |
| 1979 | May 16 | Oct 5 | 141 | May 1 | Oct 13 |
| 1980 | May 9 | Sept 26 | 139 | April 26 | Oct 4 |
| 1981 | May 12 | Oct 2 | 142 | May 12 | Oct 8 |
| 1982 | April 28 | Sept 22 | 146 | April 28 | Oct 21 |
| 1983 | May 26 | Oct 9 | 135 | May 10 | Oct 18 |
| 1984 | May 15 | Sept 16 | 123 | April 19 | Sept 29 |
| 1985 | May 2 | Sept 27 | 147 | April 9 | Nov 4 |
| 1986 | May 3 | Oct 6 | 155 | May 3 | Nov 2 |
| 1987 | May 5 | Oct 2 | 149 | April 8 | Oct 3 |
| 1988 | May 25 | Oct 5 | 132 | April 28 | Oct 6 |
| 1989 | May 12 | Sept 23 | 133 | May 7 | Sept 24 |
| 1990 | May 11 | Oct 11 | 152 | April 18 | Oct 19 |
| 1991 | April 22 | Sept 20 | 150 | April 2 | Sept 27 |
| 1992 | May 27 | Sept 29 | 124 | May 6 | Oct 17 |
| 1993 | April 26 | Sept 29 | 155 | April 21 | Sept 30 |
| 1994 | May 6 | Oct 10 | 156 | April 22 | Nov 9 |
| 1995 | April 25 | Sept 22 | 149 | April 14 | Sept 23 |
| 1996 | May 30 | Oct 2 | 124 | April 27 | Oct 3 |
| 1997 | May 21 | Oct 14 | 145 | May 16 | Oct 15 |
| 1998 | April 28 | Oct 14 | 168 | April 5 | Oct 22 |
| 1999 | April 25 | Oct 2 | 159 | March 27 | Oct 18 |
| 2000 | April 26 | Oct 6 | 162 | April 12 | Oct 9 |
| 2001 | April 18 | Oct 6 | 170 | April 18 | Oct 6 |
| 2002 | May 21 | Oct 7 | 138 | May 18 | Oct 16 |
| 2003 | May 3 | Sept 30 | 149 | April 23 | Oct 1 |
| 2004 | May 3 | Oct 4 | 153 | May 3 | Oct 5 |
| 2005 | May 4 | Oct 16 | 164 | May 4 | Oct 27 |
| 2006 | May 6 | Oct 6 | 152 | April 9 | Oct 12 |
| 2007 | April 16 | Sept 15 | 151 | April 16 | Nov 7 |
| 2008 | May 4 | Oct 4 | 152 | April 14 | Oct 28 |
| 2009 | April 22 | Oct 9 | 169 | April 12 | Oct 10 |
| 2010 | May 9 | Oct 4 | 147 | April 9 | Oct 22 |
| 2011 | May 4 | Oct 2 | 150 | May 4 | Oct 28 |
| 2012 | April 27 | Sept 24 | 149 | April 23 | Oct 12 |
| 2013 | May 13 | Oct 14 | 153 | April 20 | Oct 22 |
| 2014 | April 23 | Oct 11 | 170 | April 18 | Oct 22 |
| 2015 | April 28 | Oct 16 | 170 | April 24 | Oct 17 |
| 2016 | May 15 | Nov 9 | 177 | April 12 | Nov 11 |
| 2017 | May 3 | Oct 29 | 178 | April 1 | Oct 29 |
| 2018 | April 29 | Oct 12 | 165 | April 29 | Oct 13 |
| 2019 | April 28 | Oct 24 | 178 | April 28 | Oct 25 |
| 2020 | May 13 | Oct 2 | 141 | May 9 | Oct 19 |
| 2021 | May 11 | Oct 22 | 163 | April 22 | Nov 2 |
| 2022 | May 4 | Oct 15 | 163 | April 27 | Oct 19 |
| 2023 | April 26 | Oct 17 | 173 | April 26 | Oct 30 |
| 2024 | April 25 | Oct 16 | 173 | April 21 | Nov 21 |
| 2025 | May 9 | Oct 23 | 166 | April 16 | Oct 24 |
How We Did This
- NOAA dates: the probability dates and season lengths are NOAA's 1991-2020 U.S. Climate Normals for Madison Dane County Regional Airport (USW00014837), fields ANN-TMIN-PRBLST, PRBFST and PRBGSL.(NOAA normals)
- Our yearly dates: daily minimum temperatures for the same station from NOAA's Applied Climate Information System, 1940 to Oct 9, 2026.(NOAA ACIS) For each calendar year we took the last day before July 1 and the first day after with a low of 32°F or colder (and 28°F or colder). No year since 1940 is missing a day in the spring or fall windows.
- One site: we used the airport alone, since 1940, rather than the longer Madison Area record because the airport is the station NOAA's normals describe. Lows in town, near the lakes and in low ground can differ by several degrees.
Questions
When is the last frost in Madison, Wisconsin?
NOAA's 1991-2020 normals put the median last 32°F night at the Madison airport on May 1. There's still a 1-in-10 chance of a frost on or after May 16.
When is the first frost in Madison?
The median first 32°F night in fall is Oct. 10, by NOAA's 1991-2020 normals. One year in 10 it comes by Sept. 26; nine years in 10 by Oct. 24.
How deep is the frost line in Wisconsin?
For new one- and two-family homes, Wisconsin's Uniform Dwelling Code requires footings below the frost penetration level or at least 48 inches below grade, whichever is deeper. Check with your building inspector for decks, additions and other projects.
What's the latest frost Madison has had?
In the airport record since 1940, June 10, 1972. The earliest fall frost was Sept 12, 1955.