Frost dates for Copper Harbor, MI
At Copper Harbor, the median last spring frost (32°F) is May 10 and the median first fall frost is Oct 21, for a typical growing season of 161 days. For a 90% chance that the last frost has passed, wait until Jun 2. Nearby ZIP codes are in USDA hardiness zone 5b.
- May 10Last spring frost (median)50% chance of 32°F after this date
- Jun 2Safer planting date10% chance of 32°F after this date
- Oct 21First fall frost (median)50% chance of 32°F by this date
- 161 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | May 9 | May 27 | Jun 13 |
| 32°F | Apr 26 | May 10 | Jun 2 |
| 28°F | Apr 14 | Apr 27 | May 14 |
| 24°F | Apr 3 | Apr 17 | Apr 30 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Sep 21 | Oct 6 | Oct 21 |
| 32°F | Oct 3 | Oct 21 | Nov 5 |
| 28°F | Oct 19 | Nov 3 | Nov 18 |
| 24°F | Nov 1 | Nov 13 | Nov 27 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 108 days | 131 days | 155 days |
| 32°F | 132 days | 161 days | 183 days |
| 28°F | 164 days | 187 days | 207 days |
| 24°F | 189 days | 208 days | 228 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 49950 | 5b | -15 to -10°F | 21 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USW00094899, at 47.4667, -87.8833, elevation 191 m (626 ft).
- Data quality: Representative (10+ years), 22 years of freeze data.
- Average days per year at or below 32°F: 152.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Copper Harbor Fort Wilkins (1 km)
- Hancock Houghton Co Airport (56 km)
- Jacobsville (66 km)
- Big Bay 1nw (71 km)
- Baraga 7nw (90 km)
- Herman (97 km)
- Alberta Ford For Center (102 km)
- Champion Van Riper Pk (106 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.