Frost dates for Copper Harbor Fort Wilkins, MI
At Copper Harbor Fort Wilkins, the median last spring frost (32°F) is May 20 and the median first fall frost is Oct 15, for a typical growing season of 148 days. For a 90% chance that the last frost has passed, wait until Jun 3. Nearby ZIP codes are in USDA hardiness zone 6a.
- May 20Last spring frost (median)50% chance of 32°F after this date
- Jun 3Safer planting date10% chance of 32°F after this date
- Oct 15First fall frost (median)50% chance of 32°F by this date
- 148 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 19 | Jun 2 | Jun 16 |
| 32°F | May 3 | May 20 | Jun 3 |
| 28°F | Apr 23 | May 4 | May 21 |
| 24°F | Apr 11 | Apr 24 | May 6 |
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 19 | Oct 3 | Oct 16 |
| 32°F | Sep 30 | Oct 15 | Oct 30 |
| 28°F | Oct 13 | Oct 29 | Nov 11 |
| 24°F | Oct 27 | Nov 7 | Nov 20 |
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 | 100 days | 120 days | 140 days |
| 32°F | 125 days | 148 days | 168 days |
| 28°F | 153 days | 174 days | 194 days |
| 24°F | 179 days | 197 days | 216 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 |
|---|---|---|---|
| 49918 | 6a | -10 to -5°F | 4 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 USC00201780, at 47.4678, -87.8672, elevation 190 m (625 ft).
- Data quality: Representative (10+ years), 25 years of freeze data.
- Average days per year at or below 32°F: 167.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Copper Harbor (1 km)
- Hancock Houghton Co Airport (57 km)
- Jacobsville (67 km)
- Big Bay 1nw (71 km)
- Baraga 7nw (91 km)
- Herman (97 km)
- Alberta Ford For Center (103 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.