U.S. Frost Dates by Weather Station

NOAA station USW00014916 · North Dakota

Frost Dates for Grand Forks (Airport), ND

NOAA weather station Grand Forks International Airport (USW00014916), North Dakota · elevation 842 ft (257 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 31only 1 spring in 10 still has a frost later
  • Typical last frostMay 1650% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season133 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Grand Forks (Airport), NDSpring: a frost after May 3 in 9 years out of 10, after May 16 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 15 in 1 year out of 10, before September 27 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 133 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 16First frost ~Sep 27Frost season at Grand Forks (Airport), NDSpring: a frost after May 3 in 9 years out of 10, after May 16 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 15 in 1 year out of 10, before September 27 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 133 days.JFMAMJJASONDLast frost ~May 16First frost ~Sep 27
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 31September 15
50% (typical)May 16September 27
90% (likely)May 3October 8
Frost-free season (32°F, 50% chance)
133 days
Hard frost (28°F), last in spring, 50% chance after
May 4
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 17 (1 day later than the 30-year normal), typical first fall frost September 30 (3 days later). Frost-free season 134 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 Forks (Airport): chance of a frost after this dateSpring, chance of a frost after the date: 10% May 31, 20% May 26, 30% May 21, 40% May 18, 50% May 16, 60% May 13, 70% May 10, 80% May 7, 90% May 3. Observed last spring frost in recent years: 2021 May 28, 2022 May 21, 2023 May 2, 2024 April 24, 2025 April 29, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 31May 16May 32021: May 282022: May 212023: May 22024: April 242025: April 292026: May 20Fall at Grand Forks (Airport): chance of a frost before this dateFall, chance of a frost before the date: 10% September 15, 20% September 19, 30% September 22, 40% September 24, 50% September 27, 60% September 29, 70% October 1, 80% October 3, 90% October 8. Observed first fall frost in recent years: 2021 October 17, 2022 September 27, 2023 October 8, 2024 October 14, 2025 September 7.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 15Sep 27Oct 82021: October 172022: September 272023: October 82024: October 142025: September 7
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 28October 17
2022May 21September 27
2023May 2October 8
2024April 24October 14
2025April 29September 7
2026May 20season not over yet

What these dates mean

May 31 is the cautious spring date for Grand Forks (Airport), meaning there is only a 10 % chance of a light frost after that day; a gardener can confidently set out tender crops at that time.

The 50 % date of May 16 marks the point where a light frost is equally likely to occur later or not, and the fall median of September 27 does the same for an early frost. These dates give the gardener a sense of the middle of the frost window but are not themselves frost dates. For a cautious fall plan the gardener looks to September 15, which carries only a 10 % chance that a light frost has arrived earlier, allowing the final harvest of tender crops. A hard frost at 28 °F is more damaging than a light frost at 32 °F, so the median hard-frost dates of May 4 and October 5 are critical reference points.

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 15" 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 Forks (Airport), NDNumbered nearest stations: 1 — near Grand Forks, ND — 4 mi; 2 — near Crookston, MN — 28 mi; 3 — Argyle, MN — 32 mi; 4 — Petersburg, ND — 39 mi; 5 — Red Lake Falls, MN — 42 mi.NDMN25 mi · 40 km1. near Grand Forks, ND — 4 mi12. near Crookston, MN — 28 mi23. Argyle, MN — 32 mi34. Petersburg, ND — 39 mi45. Red Lake Falls, MN — 42 mi5
  1. near Grand Forks, ND 4 mi (7 km)
  2. near Crookston, MN 28 mi (45 km)
  3. Argyle, MN 32 mi (51 km)
  4. Petersburg, ND 39 mi (62 km)
  5. Red Lake Falls, MN 42 mi (67 km)

Sources

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

Station coordinates: 47.9428, -97.1839.