Frost dates / Wisconsin / Janesville

Frost dates in Janesville, WI

The station on this page is AFTON - JANESVILLE WWTP, WI US (USC00470045), 4.2 miles from the city point. Population in the Census 2024 estimate is 66,428.

Zone 5bUSDA average annual extreme minimum -15°F to -10°F, from ZIP 53545 (4 miles from the city point used on this page).

Median last 32°F is April 26. Median first 32°F is October 15. The 50% growing-season length is 170 days. The green band runs from the median last frost to the median first frost. Thin ticks mark the 10%, 50%, and 90% dates.

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Last 32°F in spring

NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.

Probability	Date	How to read it
90%	April 13	Earlier date. A last 32°F on or after this day is common.
50%	April 26	Median.
10%	May 11	Later date. A last 32°F on or after this day is uncommon.

First 32°F in fall

NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.

Probability	Date	How to read it
10%	October 1	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 15	Median.
90%	October 27	Later date. A first 32°F on or before this day is common.

32°F growing-season length

Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.

Probability the season is at least this long	Days
10%	190
50%	170
90%	151

28°F threshold

	10%	50%	90%
Last, on or after	April 29	April 15	April 2
First, on or before	October 12	October 26	November 7
Season at least	212 days	193 days	172 days

36°F threshold

	10%	50%	90%
Last, on or after	May 23	May 6	April 22
First, on or before	September 22	October 4	October 16
Season at least	167 days	149 days	130 days

Station AFTON - JANESVILLE WWTP, WI US (USC00470045). Completeness flag S, 29 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 100%. Freeze dates are conditional on that threshold occurring. Elevation 232.3 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.

Check a crop against this station

Janesville, WI

Zone 5bAverage annual extreme minimum -15°F to -10°F

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Wisconsin. Nearest qualified station: AFTON - JANESVILLE WWTP, WI US (USC00470045), 4.2 miles. Median last 32°F April 26. Median first 32°F October 15. The 50% growing-season length is 170 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 11	April 26	April 13
First 32°F on or before	October 1	October 15	October 27

Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.

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Planting calendar

Frost dates for Wisconsin are above. Planting windows appear for states with a cited extension guide. The fall and seed tools use the numbers you enter and the station dates.

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