U.S. Frost Dates by Weather Station

NOAA station USC00472869 · Wisconsin

Frost Dates for Fort Atkinson, WI

NOAA weather station Fort Atkinson (USC00472869), Wisconsin · elevation 800 ft (244 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 17only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season166 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Fort Atkinson, WISpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 17 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 13 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 166 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 13Frost season at Fort Atkinson, WISpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 17 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 13 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 166 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 13
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.

Frost dates (32°F)

Probability of frost, based on 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 17September 29
50% (typical)April 28October 13
90% (likely)April 14October 26
Frost-free season (32°F, 50% chance)
166 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost April 27 (1 day earlier than the 30-year normal), typical first fall frost October 16 (3 days later). Frost-free season 172 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Fort Atkinson: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 17, 20% May 10, 30% May 5, 40% May 1, 50% April 28, 60% April 25, 70% April 21, 80% April 18, 90% April 14. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 April 28, 2024 April 25, 2025 April 17, 2026 May 8.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 17Apr 28Apr 142021: May 112022: April 282023: April 282024: April 252025: April 172026: May 8Fall at Fort Atkinson: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 3, 30% October 6, 40% October 10, 50% October 13, 60% October 16, 70% October 19, 80% October 21, 90% October 26. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 18, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 13Oct 262021: October 222022: October 82023: October 182024: October 162025: October 24
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021May 11October 22
2022April 28October 8
2023April 28October 18
2024April 25October 16
2025April 17October 24
2026May 8season not over yet

What these dates mean

September 29 is the cautious fall date in Fort Atkinson for finishing the harvest of tender crops, carrying only a 10% chance that a light frost has arrived earlier. Gardeners looking for a low-risk window for late-season crops should aim for that date.

The 50% dates are April 28 for spring and October 13 for fall; each marks an even chance of a light frost. In spring the cautious date for setting out tender crops is May 17, which carries a 10% chance of a later frost, while planting on April 14 involves a 90% chance and is a gamble.

Hard frost, reflected by the 50% dates of April 16 and October 24, matters more because the lower 28 °F temperature can damage plant tissue that survives a light frost at 32 °F.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after May 17" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before September 29" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Fort Atkinson, WINumbered nearest stations: 1 — Whitewater, WI — 8 mi; 2 — Watertown, WI — 20 mi; 3 — near Janesville, WI — 21 mi; 4 — Oconomowoc, WI — 22 mi; 5 — Beloit, WI — 29 mi.WIIL25 mi · 40 km1. Whitewater, WI — 8 mi12. Watertown, WI — 20 mi23. near Janesville, WI — 21 mi34. Oconomowoc, WI — 22 mi45. Beloit, WI — 29 mi5
  1. Whitewater, WI 8 mi (12 km)
  2. Watertown, WI 20 mi (32 km)
  3. near Janesville, WI 21 mi (34 km)
  4. Oconomowoc, WI 22 mi (36 km)
  5. Beloit, WI 29 mi (47 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 42.905, -88.8589.