U.S. Frost Dates by Weather Station

NOAA station USC00478905 · Wisconsin

Frost Dates for Washington Island, WI

NOAA weather station Washington Island (USC00478905), Wisconsin · elevation 686 ft (209 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 31only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostOctober 1450% chance of a frost before it
  • Frost-free season152 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Washington Island, WISpring: a frost after April 30 in 9 years out of 10, after May 15 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 14 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 152 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Oct 14Frost season at Washington Island, WISpring: a frost after April 30 in 9 years out of 10, after May 15 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 14 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 152 days.JFMAMJJASONDLast frost ~May 15First 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 31September 28
50% (typical)May 15October 14
90% (likely)April 30October 31
Frost-free season (32°F, 50% chance)
152 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 28

The last 15 years (2006–2020 normals)

Typical last frost May 9 (6 days earlier than the 30-year normal), typical first fall frost October 23 (9 days later). Frost-free season 164 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 Washington Island: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 31, 20% May 26, 30% May 21, 40% May 18, 50% May 15, 60% May 12, 70% May 9, 80% May 5, 90% April 30. Observed last spring frost in recent years: 2021 May 12, 2022 May 24, 2023 May 26, 2024 April 26.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 31May 15Apr 302021: May 122022: May 242023: May 262024: April 26Fall at Washington Island: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 2, 30% October 7, 40% October 11, 50% October 14, 60% October 18, 70% October 21, 80% October 25, 90% October 31. Observed first fall frost in recent years: 2021 November 1, 2022 October 8, 2023 October 30, 2024 October 27.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 14Oct 312021: November 12022: October 82023: October 302024: October 27
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 12November 1
2022May 24October 8
2023May 26October 30
2024April 26October 27
2025no datano data
2026no dataseason not over yet

What these dates mean

The 152 days between the 50% dates in Washington Island bracket the period when a light frost is less likely than not, giving a gardener a window for tender crops. The 50% date is May 15 in spring and October 14 in fall; each marks the point at which there is an even chance of a 32 °F frost later (spring) or earlier (fall) and is not itself a frost date.

For a cautious plan, the spring date May 31 carries a 10 % chance of a light frost later and is the recommended day to set out tender crops, while the fall date September 28 carries a 10 % chance of a light frost earlier and is the recommended day to finish harvesting tender crops. A hard frost at 28 °F, whose 50% dates are May 3 and October 28, can damage or kill plants that would 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 31" 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 Washington Island, WINumbered nearest stations: 1 — Sturgeon Bay, WI — 40 mi; 2 — Manistique, MI — 51 mi; 3 — Frankfort, MI — 59 mi; 4 — Oconto, WI — 61 mi; 5 — near Kingsford, MI — 65 mi.WIMI25 mi · 40 km1. Sturgeon Bay, WI — 40 mi12. Manistique, MI — 51 mi23. Frankfort, MI — 59 mi34. Oconto, WI — 61 mi45. near Kingsford, MI — 65 mi5
  1. Sturgeon Bay, WI 40 mi (64 km)
  2. Manistique, MI 51 mi (83 km)
  3. Frankfort, MI 59 mi (95 km)
  4. Oconto, WI 61 mi (98 km)
  5. near Kingsford, MI 65 mi (104 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 45.3583, -86.8911.