U.S. Frost Dates by Weather Station

NOAA station USC00200230 · Michigan

Frost Dates for Ann Arbor, MI

NOAA weather station Ann Arbor University of Mich (USC00200230), Michigan · elevation 813 ft (248 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season160 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Ann Arbor, MISpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 20 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 27 in 9 years out of 10. Typical frost-free season: 160 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 13Frost season at Ann Arbor, MISpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 20 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 27 in 9 years out of 10. Typical frost-free season: 160 days.JFMAMJJASONDLast frost ~May 3First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 20September 29
50% (typical)May 3October 13
90% (likely)April 20October 27
Frost-free season (32°F, 50% chance)
160 days
Hard frost (28°F), last in spring, 50% chance after
April 23
Hard frost (28°F), first in fall, 50% chance before
October 26

The last 15 years (2006–2020 normals)

Typical last frost May 3 (same as the 30-year normal), typical first fall frost October 17 (4 days later). Frost-free season 163 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 Ann Arbor: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 14, 30% May 10, 40% May 6, 50% May 3, 60% April 30, 70% April 28, 80% April 24, 90% April 20. Observed last spring frost in recent years: 2021 May 30, 2022 May 8, 2023 May 26, 2024 April 26, 2025 May 9, 2026 May 12.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 3Apr 202021: May 302022: May 82023: May 262024: April 262025: May 92026: May 12Fall at Ann Arbor: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 3, 30% October 7, 40% October 10, 50% October 13, 60% October 15, 70% October 19, 80% October 22, 90% October 27. Observed first fall frost in recent years: 2021 October 24, 2022 October 3, 2023 October 23, 2024 October 9, 2025 October 9.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 13Oct 272021: October 242022: October 32023: October 232024: October 92025: October 9
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 30October 24
2022May 8October 3
2023May 26October 23
2024April 26October 9
2025May 9October 9
2026May 12season not over yet

What these dates mean

May 20 is the cautious spring date and allows a gardener to plan the setting out of tender crops with only a 10 % chance that a light frost will occur later. Planting on April 20 would be a gamble because the chance of a light frost later is 90 %.

The 50 % dates are points where the odds of a 32 °F light frost are even. The 50 % date is May 3 for spring and the 50 % date is October 13 for fall. The median hard-frost dates, when a 28 °F frost has a 50 % chance, are April 23 in spring and October 26 in fall. For a cautious fall schedule, September 29 is the date with only a 10 % chance that a light frost has arrived earlier, while October 27 would be a gamble because the chance of a light frost earlier is 90 %.

Hard frost at 28 °F can damage plant tissue that survives a 32 °F light frost, making it a greater concern.

How to read the probabilities

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

  • Spring: "10% after May 20" 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 Ann Arbor, MINumbered nearest stations: 1 — Detroit (Metro Airport), MI — 18 mi; 2 — Dearborn, MI — 22 mi; 3 — Adrian, MI — 32 mi; 4 — near Detroit, MI — 34 mi; 5 — near Jackson, MI — 41 mi.MI25 mi · 40 km1. Detroit (Metro Airport), MI — 18 mi12. Dearborn, MI — 22 mi23. Adrian, MI — 32 mi34. near Detroit, MI — 34 mi45. near Jackson, MI — 41 mi5
  1. Detroit (Metro Airport), MI 18 mi (28 km)
  2. Dearborn, MI 22 mi (35 km)
  3. Adrian, MI 32 mi (51 km)
  4. near Detroit, MI 34 mi (55 km)
  5. near Jackson, MI 41 mi (66 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: 42.2981, -83.6639.