U.S. Frost Dates by Weather Station

NOAA station USW00014814 · Michigan

Frost Dates for Alpena, MI

NOAA weather station Alpena WWTP (USW00014814), Michigan · elevation 590 ft (180 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 1750% chance of a frost before it
  • Frost-free season163 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Alpena, MISpring: a frost after April 21 in 9 years out of 10, after May 5 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 17 in half of the years, before November 1 in 9 years out of 10. Typical frost-free season: 163 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 17Frost season at Alpena, MISpring: a frost after April 21 in 9 years out of 10, after May 5 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 17 in half of the years, before November 1 in 9 years out of 10. Typical frost-free season: 163 days.JFMAMJJASONDLast frost ~May 5First frost ~Oct 17
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 30
50% (typical)May 5October 17
90% (likely)April 21November 1
Frost-free season (32°F, 50% chance)
163 days
Hard frost (28°F), last in spring, 50% chance after
April 23
Hard frost (28°F), first in fall, 50% chance before
October 31

The last 15 years (2006–2020 normals)

Typical last frost May 3 (2 days earlier than the 30-year normal), typical first fall frost October 21 (4 days later). Frost-free season 170 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: 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 8, 50% May 5, 60% May 2, 70% April 29, 80% April 25, 90% April 21. Observed last spring frost in recent years: 2021 May 8, 2022 April 29, 2023 April 19, 2024 April 26, 2025 May 2, 2026 May 3.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 5Apr 212021: May 82022: April 292023: April 192024: April 262025: May 22026: May 3Fall at Alpena: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 5, 30% October 10, 40% October 14, 50% October 17, 60% October 20, 70% October 23, 80% October 27, 90% November 1. Observed first fall frost in recent years: 2021 November 2, 2022 November 12, 2023 October 24, 2024 October 17, 2025 November 2.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 17Nov 12021: November 22022: November 122023: October 242024: October 172025: 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 8November 2
2022April 29November 12
2023April 19October 24
2024April 26October 17
2025May 2November 2
2026May 3season not over yet

What these dates mean

May 21 marks the cautious spring date for Alpena, when there is only a ten-percent chance of a light frost later, allowing a gardener to set out tender crops with minimal overall risk.

The median light-frost dates are May 5 and October 17; each represents a fifty-percent chance of a frost, so a gardener knows that frost is equally likely on either side of those dates. For a low-risk schedule, the cautious spring date is May 21 and the cautious fall date is September 30, which carries only a ten-percent chance that a light frost has arrived earlier.

A hard frost at 28 °F is more damaging than a light frost at 32 °F, and the median hard-frost dates are clearly April 23 in spring and October 31 in fall.

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 30" 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, MINumbered nearest stations: 1 — Alpena County Regional Airport, MI — 7 mi; 2 — Hale Loud Dam, MI — 44 mi; 3 — Onaway, MI — 46 mi; 4 — Vanderbilt, MI — 50 mi; 5 — East Tawas, MI — 54 mi.MI25 mi · 40 km1. Alpena County Regional Airport, MI — 7 mi12. Hale Loud Dam, MI — 44 mi23. Onaway, MI — 46 mi34. Vanderbilt, MI — 50 mi45. East Tawas, MI — 54 mi5
  1. Alpena County Regional Airport, MI 7 mi (11 km)
  2. Hale Loud Dam, MI 44 mi (70 km)
  3. Onaway, MI 46 mi (73 km)
  4. Vanderbilt, MI 50 mi (80 km)
  5. East Tawas, MI 54 mi (87 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: 45.0606, -83.4281.