U.S. Frost Dates by Weather Station

NOAA station USC00471568 · Wisconsin

Frost Dates for Chilton, WI

NOAA weather station Chilton (USC00471568), Wisconsin · elevation 840 ft (256 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 17only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 1450% chance of a frost before it
  • Frost-free season162 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Chilton, WISpring: a frost after April 19 in 9 years out of 10, after May 1 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 14 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 162 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 14Frost season at Chilton, WISpring: a frost after April 19 in 9 years out of 10, after May 1 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 14 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 162 days.JFMAMJJASONDLast frost ~May 1First frost ~Oct 14
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)May 1October 14
90% (likely)April 19October 30
Frost-free season (32°F, 50% chance)
162 days
Hard frost (28°F), last in spring, 50% chance after
April 22
Hard frost (28°F), first in fall, 50% chance before
October 27

The last 15 years (2006–2020 normals)

Typical last frost April 30 (1 day earlier than the 30-year normal), typical first fall frost October 19 (5 days later). Frost-free season 171 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 Chilton: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 17, 20% May 12, 30% May 7, 40% May 4, 50% May 1, 60% April 29, 70% April 27, 80% April 23, 90% April 19. Observed last spring frost in recent years: 2021 April 26, 2022 May 4, 2023 April 27, 2024 April 26, 2025 April 17, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1May 17May 1Apr 192021: April 262022: May 42023: April 272024: April 262025: April 172026: May 11Fall at Chilton: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 4, 30% October 7, 40% October 11, 50% October 14, 60% October 16, 70% October 19, 80% October 23, 90% October 30. Observed first fall frost in recent years: 2021 October 22, 2022 October 19, 2023 October 30, 2024 November 2, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 14Oct 302021: October 222022: October 192023: October 302024: November 22025: 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
2021April 26October 22
2022May 4October 19
2023April 27October 30
2024April 26November 2
2025April 17October 24
2026May 11season not over yet

What these dates mean

The cautious fall date in Chilton for finishing the harvest is September 29, when there is a 10% chance that a light frost has already arrived. For spring planting, the cautious date is May 17, which carries only a 10% chance of a light frost later. Planting before April 19 would be a gamble, as there is a 90% chance of a frost later.

The 50% dates indicate an even-odds point for frost. The 50% date in spring is May 1, at which point there is a 50% chance of a light frost later. In fall, the 50% date is October 14, with a 50% chance of a light frost earlier. A hard frost, defined as 28 °F, is more damaging than a light frost; its median dates are April 22 in spring and October 27 in fall, marking the midpoint of a higher-risk period.

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 Chilton, WINumbered nearest stations: 1 — Oshkosh, WI — 20 mi; 2 — Fond du Lac, WI — 22 mi; 3 — Plymouth, WI — 23 mi; 4 — Manitowoc, WI — 25 mi; 5 — Two Rivers, WI — 30 mi.WI25 mi · 40 km1. Oshkosh, WI — 20 mi12. Fond du Lac, WI — 22 mi23. Plymouth, WI — 23 mi34. Manitowoc, WI — 25 mi45. Two Rivers, WI — 30 mi5
  1. Oshkosh, WI 20 mi (33 km)
  2. Fond du Lac, WI 22 mi (36 km)
  3. Plymouth, WI 23 mi (36 km)
  4. Manitowoc, WI 25 mi (40 km)
  5. Two Rivers, WI 30 mi (48 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: 44.0328, -88.1469.