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Will it freeze in Janesville in the next 7 nights?
The earliest overnight low at or below 32°F in the available NWS frost forecast is Fri, Nov 6: 27°F (Fri, Nov 6, 6:00 PM CST to Sat, Nov 7, 6:00 AM CST).
Tonight: forecast low 35°F. Frost possible.
NWS forecast period: Thu, Nov 5, 6:00 PM CST to Fri, Nov 6, 6:00 AM CST.
6 of the next 7 nights are forecast at 36°F or colder, cold enough for frost on exposed plants.
- Tonight 35°F Frost possible · Mostly Cloudy
- Fri, Nov 6 27°F Hard freeze · Mostly Clear
- Sat, Nov 7 31°F Freeze · Partly Cloudy
- Sun, Nov 8 33°F Frost possible · Clear
- Mon, Nov 9 39°F Above 36°F · Mostly Clear
- Tue, Nov 10 36°F Frost possible · Partly Cloudy
- Wed, Nov 11 36°F Frost possible · Partly Cloudy
Overnight lows from the National Weather Service forecast for this location. This covers the available forecast window, not the first freeze of the whole season. Frost can form above 32°F on clear, calm nights.
Frost and freeze probabilities
Freeze dates shift from year to year. Spring percentages describe the chance of a freeze after the stated date; fall percentages describe the chance of a freeze by that date. The 10% spring date is the cautious one: a later freeze happens about 1 year in 10.
These dates describe historical probabilities, not this year’s forecast or the earliest and latest possible freezes. Different weather stations or probability thresholds can produce different published dates for the same city.
Average first hard freeze in Janesville
The median first fall hard-freeze date (28°F) is October 26, from NOAA’s 1991–2020 Climate Normals at Afton - Janesville Wastewater Plant. This is the 50% probability date, not a forecast for this year.
| Temperature | Last spring date 90% · 50% · 10% chance of a later freeze | First fall date 10% · 50% · 90% chance of an earlier freeze | Season |
|---|---|---|---|
| 36°F frost possible | Apr 22 · May 6 · May 23 | Sep 22 · Oct 4 · Oct 16 | 149 days |
| 32°F freeze | Apr 13 · Apr 26 · May 11 | Oct 1 · Oct 15 · Oct 27 | 170 days |
| 28°F hard freeze | Apr 2 · Apr 15 · Apr 29 | Oct 12 · Oct 26 · Nov 7 | 193 days |
Average high temperature by month
1991–2020 normals at Afton - Janesville Wastewater Plant
Average low temperature by month
Months with lows near or below freezing carry frost risk
Where these frost dates come from
The frost dates for Janesville, WI come from the nearest weather station with freeze statistics in NOAA’s 1991–2020 Climate Normals: Afton - Janesville Wastewater Plant (station USC00470045, elevation 762 ft), 4.2 mi from Janesville. Local conditions (valleys, hilltops, distance to water, city heat) can shift frost dates by days or weeks. The hardiness zone is from the 2023 USDA Plant Hardiness Zone Map (USDA ARS and Oregon State University PRISM). See our methodology.
Frost dates near Janesville
| City | Distance | Last spring frost | First fall frost |
|---|---|---|---|
| Milton, WI | 7.5 mi | Apr 28 | Oct 13 |
| Edgerton, WI | 11 mi | Apr 30 | Oct 11 |
| Beloit, WI | 11 mi | May 1 | Oct 12 |
| South Beloit, IL | 14 mi | May 1 | Oct 12 |
| Evansville, WI | 16 mi | Apr 30 | Oct 11 |
| Rockton, IL | 17 mi | May 1 | Oct 12 |
| Whitewater, WI | 17 mi | May 2 | Oct 9 |
| Roscoe, IL | 18 mi | May 1 | Oct 12 |
| Fort Atkinson, WI | 19 mi | Apr 28 | Oct 13 |
| Stoughton, WI | 20 mi | Apr 30 | Oct 11 |
Frequently asked questions
When is the last frost in Janesville?
On average, the last spring frost (32°F) in Janesville is around April 26. In about 1 year in 10 it comes after May 11, and in 9 years in 10 it comes after April 13.
When is the first frost in Janesville?
The first fall frost (32°F) usually arrives around October 15. There’s a 10% chance of a freeze by October 1 and a 90% chance by October 27.
Can it frost in Janesville after the last frost date?
Yes. Frost can form on clear, calm nights even when the air stays above 32°F. Temperatures of 36°F or lower, cold enough for frost on exposed plants, have a 50% chance of occurring after May 6.
What growing zone is Janesville?
Janesville is in USDA Plant Hardiness Zone 5b (average annual extreme minimum temperature −15 to −10°F), based on the 2023 USDA map for ZIP code 53545. See growing zones in Wisconsin.
More: all Wisconsin frost dates · Wisconsin growing zones · UV index today in Janesville · frost vs. freeze