USDA Hardiness Zone 5b
Frost Dates for 53546 — Janesville, Wisconsin
NOAA 1991–2020 normals from Afton - Janesville Wwtp, WI (762 ft), 4 miles southwest.
Updated
In Janesville, the last spring frost (32°F) is around April 26 in half of years and has passed by May 11 in nine years out of ten. The first fall frost comes around October 15, as early as October 1 one year in ten, leaving a typical freeze-free season of 170 days (NOAA, Afton - Janesville Wwtp, WI).
- Last spring frost
- April 26
- First fall frost
- October 15
- Growing season
- 170 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- November 25
- Last snow
- March 24
- Winters with snow
- 100%
- Snow per year
- 36.6"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Janesville
Half of springs at Afton - Janesville Wwtp, WI see their last 32°F night by April 26; only one in ten is past it by April 13, and one in ten still has one after May 11. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 5 20%, and after May 11 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 30% of the 182 Wisconsin stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 15 in half of years, as early as October 1 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 11 days later, around October 26; in spring the one-in-ten date for 28°F is April 29, 12 days before the 32°F one. The freeze-free season lasts 170 days in a typical year, longer than at 84% of the 182 Wisconsin stations; it reaches 190 days one year in ten and falls short of 151 one year in ten. On average 148 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 10 days longer, to about May 6, and return around October 4. Severe cold of 16°F or below comes every winter, usually between November 24 and March 16.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 22 | Apr 27 | May 1 | May 4 | May 6 | May 9 | May 13 | May 17 | May 23 |
| 32°F | Apr 13 | Apr 17 | Apr 20 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 5 | May 11 |
| 28°F | Apr 2 | Apr 5 | Apr 8 | Apr 12 | Apr 15 | Apr 18 | Apr 21 | Apr 25 | Apr 29 |
| 24°F | Mar 18 | Mar 24 | Mar 29 | Apr 1 | Apr 3 | Apr 5 | Apr 8 | Apr 12 | Apr 17 |
| 20°F | Mar 10 | Mar 14 | Mar 18 | Mar 21 | Mar 24 | Mar 28 | Mar 31 | Apr 3 | Apr 6 |
| 16°F | Mar 2 | Mar 7 | Mar 10 | Mar 14 | Mar 16 | Mar 19 | Mar 21 | Mar 25 | Mar 30 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 22 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 12 | Oct 16 |
| 32°F | Oct 1 | Oct 6 | Oct 10 | Oct 12 | Oct 15 | Oct 17 | Oct 20 | Oct 23 | Oct 27 |
| 28°F | Oct 12 | Oct 16 | Oct 20 | Oct 23 | Oct 26 | Oct 28 | Oct 31 | Nov 3 | Nov 7 |
| 24°F | Oct 24 | Oct 30 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 11 | Nov 16 | Nov 20 |
| 20°F | Nov 2 | Nov 6 | Nov 9 | Nov 13 | Nov 15 | Nov 19 | Nov 22 | Nov 25 | Dec 1 |
| 16°F | Nov 10 | Nov 15 | Nov 19 | Nov 21 | Nov 24 | Nov 28 | Dec 1 | Dec 5 | Dec 12 |
Freeze probabilities 1991–2020 at Afton - Janesville Wwtp, WI, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 53546 →Compare Janesville with another place →
Weather by month in Janesville
July is the warmest month at Afton - Janesville Wwtp, WI, averaging 83°F by day and 62°F at night; January is the coldest at 28°F and 12°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 32% of years.
Warmth for growing adds up to 2,831 growing degree days a year (base 50°F), more than at 94% of the 182 Wisconsin stations. 34% of them (956) have built up by the end of June, and July adds the most, 699. Precipitation totals 37.4 inches a year, most in June (5.0") and least in January (1.6"); May to September bring 57% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 28 | 12 | 1.6 | 100% | 30 | 0 |
| Feb | 32 | 15 | 1.6 | 100% | 26 | 1 |
| Mar | 45 | 25 | 2.1 | 100% | 24 | 15 |
| Apr | 58 | 36 | 3.6 | 100% | 10 | 74 |
| May | 70 | 48 | 4.1 | 32% | 1 | 297 |
| Jun | 80 | 58 | 5.0 | 0% | 0 | 569 |
| Jul | 83 | 62 | 4.2 | 0% | 0 | 699 |
| Aug | 82 | 60 | 4.3 | 0% | 0 | 639 |
| Sep | 75 | 51 | 3.7 | 10% | <1 | 397 |
| Oct | 62 | 40 | 3.0 | 94% | 8 | 124 |
| Nov | 46 | 29 | 2.3 | 100% | 21 | 15 |
| Dec | 34 | 18 | 1.9 | 100% | 29 | 1 |
Monthly normals 1991–2020 at Afton - Janesville Wwtp, WI (762 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Clinton Wwtp, WI, 10 miles southeast of Janesville and 162 feet higher, has a last frost 4 days later (April 30), a first frost 5 days earlier (October 10), a season 9 days shorter.
When it snows in Janesville, Wisconsin
The first measurable snow (0.1 inch or more) in Janesville usually arrives around November 25, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Afton - Janesville Wwtp, WI, 4 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 33 days after the last snow.
Planting calendar for 53546
| When | What to do |
|---|---|
| February 15 – March 1 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 1 – March 15 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 29 – April 12 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 26 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 23 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 1 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 15 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 53546 is 4 miles from Afton - Janesville Wwtp, WI, which stands at 762 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 53546 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across Wisconsin →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.