U.S. Frost Dates by Weather Station

NOAA station USC00202015 · Michigan

Frost Dates for Dearborn, MI

NOAA weather station Dearborn (USC00202015), Michigan · elevation 605 ft (184 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 18only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 1550% chance of a frost before it
  • Frost-free season166 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Dearborn, MISpring: a frost after April 17 in 9 years out of 10, after May 1 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 15 in half of the years, before October 28 in 9 years out of 10. Typical frost-free season: 166 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 15Frost season at Dearborn, MISpring: a frost after April 17 in 9 years out of 10, after May 1 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 15 in half of the years, before October 28 in 9 years out of 10. Typical frost-free season: 166 days.JFMAMJJASONDLast frost ~May 1First frost ~Oct 15
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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 18October 1
50% (typical)May 1October 15
90% (likely)April 17October 28
Frost-free season (32°F, 50% chance)
166 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 28

The last 15 years (2006–2020 normals)

Typical last frost May 2 (1 day later than the 30-year normal), typical first fall frost October 20 (5 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 Dearborn: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 18, 20% May 12, 30% May 8, 40% May 4, 50% May 1, 60% April 29, 70% April 26, 80% April 22, 90% April 17. Observed last spring frost in recent years: 2022 April 29, 2023 April 27, 2024 April 26, 2025 April 17, 2026 April 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 18May 1Apr 172022: April 292023: April 272024: April 262025: April 172026: April 20Fall at Dearborn: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 6, 30% October 9, 40% October 12, 50% October 15, 60% October 18, 70% October 21, 80% October 24, 90% October 28. Observed first fall frost in recent years: 2022 October 8, 2023 October 23, 2024 October 17, 2025 November 2.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 15Oct 282022: October 82023: October 232024: 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
2021no dataincomplete record
2022April 29October 8
2023April 27October 23
2024April 26October 17
2025April 17November 2
2026April 20season not over yet

What these dates mean

May 18 is the cautious spring date in Dearborn, giving a gardener the basis for setting out tender crops when the chance of a later light frost is only 10 %. The comparable cautious fall date is October 1, when there is a 10 % chance that a light frost has already arrived, so it marks the latest reliable time to finish harvesting tender crops.

May 1 carries a 50 % chance of a light frost later than this date, and October 15 carries a 50 % chance of a light frost earlier than this date; these dates are not frost thresholds themselves. The median hard-frost dates are April 20 in spring and October 28 in fall, each representing a 50 % chance of a hard frost later (spring) or earlier (fall).

Hard frosts at 28 °F can damage plants that survive a light frost at 32 °F, making them a more critical risk.

How to read the probabilities

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

  • Spring: "10% after May 18" 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 October 1" 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 Dearborn, MINumbered nearest stations: 1 — Detroit (Metro Airport), MI — 8 mi; 2 — near Detroit, MI — 13 mi; 3 — Ann Arbor, MI — 22 mi; 4 — Adrian, MI — 49 mi; 5 — near Toledo, OH — 58 mi.MIOHIN25 mi · 40 km1. Detroit (Metro Airport), MI — 8 mi12. near Detroit, MI — 13 mi23. Ann Arbor, MI — 22 mi34. Adrian, MI — 49 mi45. near Toledo, OH — 58 mi5
  1. Detroit (Metro Airport), MI 8 mi (12 km)
  2. near Detroit, MI 13 mi (21 km)
  3. Ann Arbor, MI 22 mi (35 km)
  4. Adrian, MI 49 mi (78 km)
  5. near Toledo, OH 58 mi (94 km)

Sources

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

Station coordinates: 42.3194, -83.2378.