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 freeze dates of the winter for locations around northeast Minnesota and northwest Wisconsin
| 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 entire period of record) |
10/1 |
9/15 |
9/15 |
9/21 |
9/18 |
|
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 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 Freeze (based on entire period of record) |
10/12 |
9/29 |
9/26 |
10/2 |
9/29 |
|
Latest First 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 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 entire period of record) |
5/14 |
5/26 |
5/26 |
5/14 |
6/01 |
|
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 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 Freeze (based on entire period of record) |
4/30 |
5/13 |
5/13 |
5/4 |
5/16 |
|
Latest Last 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) |
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