U.S. Frost Dates by Weather Station

NOAA station USC00213296 · Minnesota

Frost Dates for Grand Portage, MN

NOAA weather station Grand Portage (USC00213296), Minnesota · elevation 730 ft (223 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 5only 1 spring in 10 still has a frost later
  • Typical last frostMay 2450% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season127 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Grand Portage, MNSpring: a frost after May 7 in 9 years out of 10, after May 24 in half of the years, after June 5 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 29 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 127 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 24First frost ~Sep 29Frost season at Grand Portage, MNSpring: a frost after May 7 in 9 years out of 10, after May 24 in half of the years, after June 5 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 29 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 127 days.JFMAMJJASONDLast frost ~May 24First frost ~Sep 29
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 5September 16
50% (typical)May 24September 29
90% (likely)May 7October 10
Frost-free season (32°F, 50% chance)
127 days
Hard frost (28°F), last in spring, 50% chance after
May 9
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 23 (1 day earlier than the 30-year normal), typical first fall frost October 2 (3 days later). Frost-free season 131 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 Portage: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 5, 20% June 1, 30% May 29, 40% May 26, 50% May 24, 60% May 21, 70% May 17, 80% May 13, 90% May 7. Observed last spring frost in recent years: 2021 May 29, 2022 May 24, 2023 May 25, 2024 May 10, 2025 May 19, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 5May 24May 72021: May 292022: May 242023: May 252024: May 102025: May 192026: May 22Fall at Grand Portage: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 21, 30% September 24, 40% September 26, 50% September 29, 60% October 1, 70% October 3, 80% October 6, 90% October 10. Observed first fall frost in recent years: 2021 October 21, 2022 September 28, 2023 October 17, 2024 October 4, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 29Oct 102021: October 212022: September 282023: October 172024: October 42025: October 8
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 24September 28
2023May 25October 17
2024May 10October 4
2025May 19October 8
2026May 22season not over yet

What these dates mean

June 5 is the cautious spring date for light frost, giving a gardener confidence to set out tender crops after the risk of a later frost drops to ten percent. The 50% light-frost dates are May 24 in spring and September 29 in fall, meaning the chance of a frost is exactly fifty percent on each of those days. The cautious fall date is September 16, indicating only a ten-percent chance that a frost has already arrived and allowing a gardener to finish harvesting tender crops. Hard frost thresholds are lower, with the 50% hard-frost dates on May 9 and October 9; a temperature of 28 °F can damage plants that would survive a light frost, making it a more severe concern. Therefore it is a key factor in planning winter protection.

How to read the probabilities

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

  • Spring: "10% after June 5" 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 16" 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 Portage, MNNumbered nearest stations: 1 — Grand Marais, MN — 33 mi; 2 — Hancock, MI — 79 mi; 3 — Wolf Ridge Elc, MN — 80 mi; 4 — Bergland Dam, MI — 96 mi; 5 — Madeline Island, WI — 97 mi.MIMN25 mi · 40 km1. Grand Marais, MN — 33 mi12. Hancock, MI — 79 mi23. Wolf Ridge Elc, MN — 80 mi34. Bergland Dam, MI — 96 mi45. Madeline Island, WI — 97 mi5
  1. Grand Marais, MN 33 mi (53 km)
  2. Hancock, MI 79 mi (128 km)
  3. Wolf Ridge Elc, MN 80 mi (128 km)
  4. Bergland Dam, MI 96 mi (154 km)
  5. Madeline Island, WI 97 mi (155 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 47.9711, -89.6908.