Frost dates for Afton - Janesville Wastewater Plant, WI
At Afton - Janesville Wastewater Plant, the median last spring frost (32°F) is Apr 26 and the median first fall frost is Oct 15, for a typical growing season of 170 days. For a 90% chance that the last frost has passed, wait until May 11. Nearby ZIP codes are in USDA hardiness zone 5b.
- Apr 26Last spring frost (median)50% chance of 32°F after this date
- May 11Safer planting date10% chance of 32°F after this date
- Oct 15First fall frost (median)50% chance of 32°F by this date
- 170 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 22 | May 6 | May 23 |
| 32°F | Apr 13 | Apr 26 | May 11 |
| 28°F | Apr 2 | Apr 15 | Apr 29 |
| 24°F | Mar 18 | Apr 3 | Apr 17 |
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 22 | Oct 4 | Oct 16 |
| 32°F | Oct 1 | Oct 15 | Oct 27 |
| 28°F | Oct 12 | Oct 26 | Nov 7 |
| 24°F | Oct 24 | Nov 5 | 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 | 130 days | 149 days | 167 days |
| 32°F | 151 days | 170 days | 190 days |
| 28°F | 172 days | 193 days | 212 days |
| 24°F | 198 days | 216 days | 235 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 |
|---|---|---|---|
| 53548 | 5b | -15 to -10°F | 8 km |
| 53546 | 5b | -15 to -10°F | 10 km |
| 53545 | 5b | -15 to -10°F | 11 km |
| 53537 | 5b | -15 to -10°F | 13 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 USC00470045, at 42.6375, -89.0642, elevation 232 m (762 ft).
- Data quality: Standard (24+ years of data), 29 years of freeze data.
- Average days per year at or below 32°F: 148.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Beloit (15 km)
- Clinton Wastewater Plant (18 km)
- Brodhead Wastewater Plant (26 km)
- Stoughton (33 km)
- Delavan Wastewater Plant (33 km)
- Fort Atkinson (34 km)
- Whitewater (36 km)
- Jefferson Wastewater Plant (45 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.