Before continuing, here are a few definitions...
Frost occurs when there is a solid deposition of water vapor from the air. Frost will form when solid surfaces are cooled below the dew point. An air temperature range of 33°- 36° (or colder), along with light winds, is usually needed to initiate frost formation. At least minor damage is possible to plants. One must keep in mind that frost is not guaranteed if the air is very dry and/or winds are roughly 8+ MPH.
Freeze occurs when the temperature drops to 32°-or-lower. A freeze will result in significant damage to many unprotected plants, especially if the temperature remains at-or-below freezing for several hours.
Hard freeze typically occurs when the temperature reaches 28°-or-lower for at least an hour (or more). This usually means that most seasonal vegetation will be destroyed. In addition, there is a possibility of damage to unprotected outdoor plumbing/un-drained sprinkler systems etc.
Average first and last frost and freeze dates of the winter for locations around northeast Minnesota and northwest Wisconsin
NOTE: For simplicity, July 16 denotes the "first fall day" and July 15 denotes the "last spring day". Since temperatures cold enough to produce frost have been observed at all climate sites during all months of the year, a single-date cutoff must be chosen. Indeed, many ≤36°F days have been observed in June, July, and August, and there have even been a few instances of freezing temperatures in July (Low of 32°F at Hibbing on 7/5/2001; Low of 32°F at International Falls on 7/11/1911; Low of 32°F at Ashland on 7/25/1915).
| Earliest/Mean/Latest First Fall Frost Climatology (≤36°F) | |||||
|
Duluth |
Hibbing |
International Falls |
Brainerd |
Ashland |
|
|
Earliest First Frost |
8/14/1964 (36°F) |
7/23/2002 (36°F) |
7/20/1912 (36°F) |
7/23/1978 (36°F) |
7/18/1924 (34°F) |
|
Mean First Frost (based on 1991-2020 normals) |
9/20 |
8/22 |
8/25 |
9/17 |
9/11 |
|
Latest First Frost |
10/19/1938 (35°F) |
10/1/1948 (35°F), 10/1/1944 (31°F) |
9/29/1920 (28°F) |
10/15/2021 (36°F) |
10/8/2016 (35°F) |
| Earliest/Mean/Latest First Fall Freeze Climatology (≤32°F) | |||||
|
Duluth |
Hibbing |
International Falls |
Brainerd |
Ashland |
|
|
Earliest First Freeze |
8/27/1986 (32°F) |
8/13/2004 (32°F) |
8/20/1907 (32°F) |
8/6/1977 (30°F), 8/6/1917 (31°F) |
8/18/1950 (32°F), 8/18/1924 (32°F) |
|
Mean First Freeze (based on 1991-2020 normals) |
9/30 |
9/8 |
9/15 |
9/25 |
9/24 |
|
Latest First Freeze |
11/6/1900 (32°F) |
10/18/1960 (31°F) |
10/17/2021 (30°F) |
10/17/2021 (31°F), 10/17/2019 (31°F) |
10/18/2021 (31°F) |
|
Earliest/Mean/Latest First Fall Hard Freeze Climatology (≤28°F) |
|||||
|
Duluth |
Hibbing |
International Falls |
Brainerd |
Ashland |
|
|
Earliest First Hard Freeze |
9/15/2007 (28°F), 9/15/1964 (27°F) |
8/21/2004 (27°F) |
8/31/1906 (27°F) |
9/1/1974 (28°F) |
9/9/1956 (27°F) |
|
Mean First Hard Freeze (based on 1991-2020 normals) |
10/9 |
9/22 |
9/24 |
10/6 |
10/3 |
|
Latest First Hard Freeze |
11/18/2016 (26°F) |
11/7/1956 (26°F) |
10/28/1963 (24°F) |
10/29/1963 (24°F) |
10/25/2013 (27°F) |
|
Earliest/Mean/Latest Last Spring Frost Climatology (≤36°F) |
|||||
|
Duluth |
Hibbing |
International Falls |
Brainerd |
Ashland |
|
|
Earliest Last Frost |
4/25/1896 (36°F) |
5/11/1960 (36°F) |
4/29/1922 (36°F) |
5/5/1936 (35°F) |
5/13/1911 (30°F) |
|
Mean Last Frost (based on 1991-2020 normals) |
5/26 |
6/13 |
6/7 |
5/25 |
6/6 |
|
Latest Last Frost |
7/5/1967 (36°F) |
7/14/1987 (35°F) |
7/12/2009 (35°F), 7/12/1926 (36°F) |
7/2/1917 (35°F) |
7/10/1968 (35°F) |
|
Earliest/Mean/Latest Last Spring Freeze Climatology (≤32°F) |
|||||
|
Duluth |
Hibbing |
International Falls |
Brainerd |
Ashland |
|
|
Earliest Last Freeze |
4/15/1899 (32°F) |
4/22/1952 (32°F) |
4/27/1922 (32°F) |
4/18/1985 (32°F) |
5/4/1908 (26°F) |
|
Mean Last Freeze (based on 1991-2020 normals) |
5/14 |
5/31 |
5/27 |
5/11 |
5/29 |
|
Latest Last Freeze |
6/21/1992 (30°F) |
7/5/2001 (32°F) |
7/11/1911 (30°F) |
6/22/1917 (30°F) |
7/25/1915 (32°F) |
|
Earliest/Mean/Latest Last Spring Hard Freeze Climatology (≤28°F) |
|||||
|
Duluth |
Hibbing |
International Falls |
Brainerd |
Ashland |
|
|
Earliest Last Hard Freeze |
4/11/1941 (28°F) |
4/14/1952 (28°F) |
4/16/1985 (21°F) |
4/11/193.7 (25°F) |
4/18/2001 (24°F) |
|
Mean Last Hard Freeze (based on 1991-2020 normals) |
5/1 |
5/19 |
5/13 |
5/2 |
5/10 |
|
Latest Last Hard Freeze |
6/10/1972 (27°F) |
6/13/2019 (28°F) |
6/16/1912 (27°F) |
6/20/1917 (28°F) |
6/10/1972 (28°F) |
Last Updated: 9/18/2024
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