U.S. Frost Dates by Weather Station

NOAA station USC00478267 · Wisconsin

Frost Dates for Sturgeon Bay, WI

NOAA weather station Sturgeon Bay Experiment Farm (USC00478267), Wisconsin · elevation 699 ft (213 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 850% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season157 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Sturgeon Bay, WISpring: a frost after April 25 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 13 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 157 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 8First frost ~Oct 13Frost season at Sturgeon Bay, WISpring: a frost after April 25 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 13 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 157 days.JFMAMJJASONDLast frost ~May 8First 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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 21September 28
50% (typical)May 8October 13
90% (likely)April 25October 30
Frost-free season (32°F, 50% chance)
157 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 28

The last 15 years (2006–2020 normals)

Typical last frost May 8 (same as the 30-year normal), typical first fall frost October 19 (6 days later). Frost-free season 160 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 Sturgeon Bay: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 17, 30% May 13, 40% May 10, 50% May 8, 60% May 5, 70% May 2, 80% April 29, 90% April 25. Observed last spring frost in recent years: 2021 May 12, 2022 May 6, 2023 May 2, 2024 April 26, 2025 May 1, 2026 May 12.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 8Apr 252021: May 122022: May 62023: May 22024: April 262025: May 12026: May 12Fall at Sturgeon Bay: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 3, 30% October 6, 40% October 10, 50% October 13, 60% October 17, 70% October 20, 80% October 24, 90% October 30. Observed first fall frost in recent years: 2021 October 24, 2022 October 27, 2023 October 9, 2024 November 10, 2025 November 2.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 13Oct 302021: October 242022: October 272023: October 92024: November 102025: November 2
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 24
2022May 6October 27
2023May 2October 9
2024April 26November 10
2025May 1November 2
2026May 12season not over yet

What these dates mean

May 21, the cautious spring date with a 10% chance of a light frost later, marks the point when a gardener can plan to set out tender crops.

The 50% light-frost dates are May 8 and October 13; they indicate an even chance of a frost occurring after the spring date or before the fall date. The median hard-frost dates are April 26 and October 28, showing when a 28 °F frost is as likely as not.

September 28, the cautious fall date with only a 10% chance that a light frost has arrived earlier, is the reference for finishing the harvest of tender crops. A hard frost at 28 °F can damage plants more severely than a light frost at 32 °F, so those median hard-frost dates are especially relevant.

How to read the probabilities

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

  • Spring: "10% after May 21" 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 28" 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 Sturgeon Bay, WINumbered nearest stations: 1 — Kewaunee, WI — 30 mi; 2 — Oconto, WI — 30 mi; 3 — Washington Island, WI — 40 mi; 4 — Green Bay, WI — 46 mi; 5 — Two Rivers, WI — 52 mi.WIMI25 mi · 40 km1. Kewaunee, WI — 30 mi12. Oconto, WI — 30 mi23. Washington Island, WI — 40 mi34. Green Bay, WI — 46 mi45. Two Rivers, WI — 52 mi5
  1. Kewaunee, WI 30 mi (48 km)
  2. Oconto, WI 30 mi (49 km)
  3. Washington Island, WI 40 mi (64 km)
  4. Green Bay, WI 46 mi (75 km)
  5. Two Rivers, WI 52 mi (84 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: 44.88, -87.3358.