U.S. Frost Dates by Weather Station

NOAA station USW00094849 · Michigan

Frost Dates for Alpena County Regional Airport, MI

NOAA weather station Alpena County Regional Airport (USW00094849), Michigan · elevation 684 ft (209 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 31only 1 spring in 10 still has a frost later
  • Typical last frostMay 1750% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season136 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Alpena County Regional Airport, MISpring: a frost after May 1 in 9 years out of 10, after May 17 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 1 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 136 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 17First frost ~Oct 1Frost season at Alpena County Regional Airport, MISpring: a frost after May 1 in 9 years out of 10, after May 17 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 1 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 136 days.JFMAMJJASONDLast frost ~May 17First frost ~Oct 1
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 31September 18
50% (typical)May 17October 1
90% (likely)May 1October 16
Frost-free season (32°F, 50% chance)
136 days
Hard frost (28°F), last in spring, 50% chance after
May 4
Hard frost (28°F), first in fall, 50% chance before
October 15

The last 15 years (2006–2020 normals)

Typical last frost May 13 (4 days earlier than the 30-year normal), typical first fall frost October 5 (4 days later). Frost-free season 144 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 Alpena County Regional Airport: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 31, 20% May 27, 30% May 23, 40% May 20, 50% May 17, 60% May 13, 70% May 10, 80% May 6, 90% May 1. Observed last spring frost in recent years: 2021 May 30, 2022 May 8, 2023 May 26, 2024 April 26, 2025 May 9, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 31May 17May 12021: May 302022: May 82023: May 262024: April 262025: May 92026: May 22Fall at Alpena County Regional Airport: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 24, 30% September 27, 40% September 30, 50% October 1, 60% October 4, 70% October 6, 80% October 10, 90% October 16. Observed first fall frost in recent years: 2021 October 22, 2022 September 29, 2023 October 22, 2024 October 10, 2025 October 16.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 18Oct 1Oct 162021: October 222022: September 292023: October 222024: October 102025: October 16
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 22
2022May 8September 29
2023May 26October 22
2024April 26October 10
2025May 9October 16
2026May 22season not over yet

What these dates mean

May 31 marks the cautious spring date at Alpena County Regional Airport; with only a ten-percent chance of a light frost after that day, a gardener can plan to set out tender crops with confidence.

The 50 % light-frost dates are May 17 in spring and October 1 in fall, meaning the chance of a frost is equal on those days. The 50 % hard-frost dates are May 4 and October 15, indicating an even odds of temperatures reaching 28 °F. For a cautious autumn schedule, September 18 is the fall date that carries only a ten-percent chance of a light frost earlier, signaling when tender crops should be finished.

A hard frost is more damaging than a light frost because the lower temperature can kill plant tissue that survives a 32 °F dip.

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 18" 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 Alpena County Regional Airport, MINumbered nearest stations: 1 — Alpena, MI — 7 mi; 2 — Onaway, MI — 40 mi; 3 — Hale Loud Dam, MI — 43 mi; 4 — Vanderbilt, MI — 43 mi; 5 — East Tawas, MI — 55 mi.MI25 mi · 40 km1. Alpena, MI — 7 mi12. Onaway, MI — 40 mi23. Hale Loud Dam, MI — 43 mi34. Vanderbilt, MI — 43 mi45. East Tawas, MI — 55 mi5
  1. Alpena, MI 7 mi (11 km)
  2. Onaway, MI 40 mi (64 km)
  3. Hale Loud Dam, MI 43 mi (69 km)
  4. Vanderbilt, MI 43 mi (70 km)
  5. East Tawas, MI 55 mi (88 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: 45.0717, -83.5644.