U.S. Frost Dates by Weather Station

NOAA station USC00213282 · Minnesota

Frost Dates for Grand Marais, MN

NOAA weather station Grand Marais (USC00213282), Minnesota · elevation 612 ft (187 m) · hardiness zone 5a*

  • Lower-risk planting dateafter June 6only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostOctober 550% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Grand Marais, MNSpring: a frost after May 3 in 9 years out of 10, after May 20 in half of the years, after June 6 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 5 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Oct 5Frost season at Grand Marais, MNSpring: a frost after May 3 in 9 years out of 10, after May 20 in half of the years, after June 6 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 5 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 137 days.JFMAMJJASONDLast frost ~May 20First frost ~Oct 5
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)June 6September 22
50% (typical)May 20October 5
90% (likely)May 3October 20
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 4
Hard frost (28°F), first in fall, 50% chance before
October 17

The last 15 years (2006–2020 normals)

Typical last frost May 21 (1 day later than the 30-year normal), typical first fall frost October 9 (4 days later). Frost-free season 139 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 Grand Marais: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 6, 20% June 1, 30% May 27, 40% May 23, 50% May 20, 60% May 17, 70% May 13, 80% May 9, 90% May 3. Observed last spring frost in recent years: 2021 May 29, 2022 May 23, 2024 April 26, 2025 May 19, 2026 May 21.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 6May 20May 32021: May 292022: May 232024: April 262025: May 192026: May 21Fall at Grand Marais: chance of a frost before this dateFall, chance of a frost before the date: 10% September 22, 20% September 26, 30% September 29, 40% October 2, 50% October 5, 60% October 8, 70% October 11, 80% October 14, 90% October 20. Observed first fall frost in recent years: 2021 October 21, 2022 October 14, 2023 October 8, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 22Oct 5Oct 202021: October 212022: October 142023: October 82024: October 162025: October 24
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 29October 21
2022May 23October 14
2023incomplete recordOctober 8
2024April 26October 16
2025May 19October 24
2026May 21season not over yet

What these dates mean

Setting out tender crops on the early spring date, May 3, carries a 90 % chance of a light frost later in the season for Grand Marais, so planting then is a gamble. The cautious spring date for tender crops is June 6, when only a 10 % chance of a light frost remains later, while the 50 % date, May 20, is the day on which a light frost has an even chance of having occurred.

In the autumn the cautious date to finish harvesting tender crops is September 22, with only a 10 % chance that a light frost has already arrived, and the 50 % date, October 5, splits the odds for a frost earlier versus later; the gamble date, October 20, carries a 90 % chance of a frost already having begun. The hard-frost 50 % dates are May 4 in spring and October 17 in fall; a hard frost at 28 °F can damage plants that survive a light frost at 32 °F, making those dates especially relevant for gardeners.

How to read the probabilities

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

  • Spring: "10% after June 6" 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 22" 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 Grand Marais, MNNumbered nearest stations: 1 — Grand Portage, MN — 33 mi; 2 — Wolf Ridge Elc, MN — 46 mi; 3 — Madeline Island, WI — 70 mi; 4 — Two Harbors, MN — 80 mi; 5 — Bergland Dam, MI — 88 mi.MN25 mi · 40 km1. Grand Portage, MN — 33 mi12. Wolf Ridge Elc, MN — 46 mi23. Madeline Island, WI — 70 mi34. Two Harbors, MN — 80 mi45. Bergland Dam, MI — 88 mi5
  1. Grand Portage, MN 33 mi (53 km)
  2. Wolf Ridge Elc, MN 46 mi (75 km)
  3. Madeline Island, WI 70 mi (113 km)
  4. Two Harbors, MN 80 mi (129 km)
  5. Bergland Dam, MI 88 mi (142 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 47.7517, -90.3283.