U.S. Frost Dates by Weather Station

NOAA station USW00014898 · Wisconsin

Frost Dates for Green Bay, WI

NOAA weather station Green Bay (USW00014898), Wisconsin · elevation 682 ft (208 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 950% chance of a frost before it
  • Frost-free season161 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Green Bay, WISpring: a frost after April 16 in 9 years out of 10, after April 30 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 9 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 161 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 9Frost season at Green Bay, WISpring: a frost after April 16 in 9 years out of 10, after April 30 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 9 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 161 days.JFMAMJJASONDLast frost ~Apr 30First frost ~Oct 9
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 16September 24
50% (typical)April 30October 9
90% (likely)April 16October 26
Frost-free season (32°F, 50% chance)
161 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost April 30 (same as the 30-year normal), typical first fall frost October 14 (5 days later). Frost-free season 167 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 Green Bay: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 11, 30% May 7, 40% May 4, 50% April 30, 60% April 29, 70% April 25, 80% April 22, 90% April 16. Observed last spring frost in recent years: 2021 May 12, 2022 April 28, 2023 April 26, 2024 April 25, 2025 April 16, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1May 16Apr 30Apr 162021: May 122022: April 282023: April 262024: April 252025: April 162026: May 11Fall at Green Bay: chance of a frost before this dateFall, chance of a frost before the date: 10% September 24, 20% September 29, 30% October 3, 40% October 6, 50% October 9, 60% October 12, 70% October 16, 80% October 21, 90% October 26. Observed first fall frost in recent years: 2021 October 23, 2022 October 19, 2023 October 29, 2024 October 16, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 24Oct 9Oct 262021: October 232022: October 192023: October 292024: October 162025: October 23
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 12October 23
2022April 28October 19
2023April 26October 29
2024April 25October 16
2025April 16October 23
2026May 11season not over yet

What these dates mean

May 16 marks the cautious spring light-frost date, with only a 10 % chance of a frost later, and it lets a gardener set out tender crops.

The 50 % date is April 30 for light frost in spring, indicating an even chance of a frost later, and the 50 % date is October 9 for light frost in fall, indicating an even chance of a frost earlier. The span between these two 32 °F median dates is 161 days.

September 24 is the cautious fall light-frost date, carrying a 10 % chance of a frost earlier, so it guides the latest time to finish harvesting tender crops. The 50 % hard-frost dates are April 17 in spring and October 24 in fall, and hard frost at 28 °F can damage plants that survive a 32 °F light frost.

How to read the probabilities

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

  • Spring: "10% after May 16" 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 24" 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 Green Bay, WINumbered nearest stations: 1 — Oconto, WI — 28 mi; 2 — Kewaunee, WI — 30 mi; 3 — Shawano, WI — 31 mi; 4 — New London, WI — 32 mi; 5 — Chilton, WI — 32 mi.25 mi · 40 km1. Oconto, WI — 28 mi12. Kewaunee, WI — 30 mi23. Shawano, WI — 31 mi34. New London, WI — 32 mi45. Chilton, WI — 32 mi5
  1. Oconto, WI 28 mi (45 km)
  2. Kewaunee, WI 30 mi (48 km)
  3. Shawano, WI 31 mi (50 km)
  4. New London, WI 32 mi (51 km)
  5. Chilton, WI 32 mi (52 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: 44.4983, -88.1111.