Frost dates for Grafton Wastewater Plant, WI
At Grafton Wastewater Plant, the median last spring frost (32°F) is Apr 23 and the median first fall frost is Oct 24, for a typical growing season of 182 days. For a 90% chance that the last frost has passed, wait until May 9. Nearby ZIP codes are in USDA hardiness zones 5b to 6a.
- Apr 23Last spring frost (median)50% chance of 32°F after this date
- May 9Safer planting date10% chance of 32°F after this date
- Oct 24First fall frost (median)50% chance of 32°F by this date
- 182 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 | Apr 20 | May 5 | May 23 |
| 32°F | Apr 10 | Apr 23 | May 9 |
| 28°F | Mar 31 | Apr 11 | Apr 24 |
| 24°F | Mar 18 | Apr 2 | Apr 13 |
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 27 | Oct 11 | Oct 26 |
| 32°F | Oct 8 | Oct 24 | Nov 5 |
| 28°F | Oct 21 | Nov 2 | Nov 15 |
| 24°F | Nov 1 | Nov 12 | Nov 25 |
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 | 135 days | 156 days | 177 days |
| 32°F | 161 days | 182 days | 200 days |
| 28°F | 186 days | 205 days | 223 days |
| 24°F | 208 days | 225 days | 243 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 |
|---|---|---|---|
| 53024 | 6a | -10 to -5°F | 3 km |
| 53012 | 5b | -15 to -10°F | 6 km |
| 53097 | 5b | -15 to -10°F | 9 km |
| 53092 | 6a | -10 to -5°F | 10 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 USC00473198, at 43.3081, -87.9553, elevation 226 m (741 ft).
- Data quality: Representative (10+ years), 12 years of freeze data.
- Average days per year at or below 32°F: 134.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Saukville Wastewater Plant (8 km)
- Port Washington (12 km)
- West Bend (12 km)
- Germantown (16 km)
- Jackson (17 km)
- W Bend Public Works (22 km)
- Richfield 3 SSW (23 km)
- Belgium Wastewater Plant (24 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.