U.S. Frost Dates by Weather Station

NOAA station USC00323621 · North Dakota

Frost Dates near Grand Forks, ND

NOAA weather station Grand Forks University (NWS) (USC00323621), North Dakota · elevation 830 ft (253 m) · hardiness zone 4a*

Grand Forks is the nearest town to the station (3.0 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season144 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season near Grand Forks, NDSpring: a frost after April 28 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 144 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Oct 1Frost season near Grand Forks, NDSpring: a frost after April 28 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 144 days.JFMAMJJASONDLast frost ~May 10First frost ~Oct 1
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 24September 20
50% (typical)May 10October 1
90% (likely)April 28October 15
Frost-free season (32°F, 50% chance)
144 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 11 (1 day later than the 30-year normal), typical first fall frost October 6 (5 days later). Frost-free season 148 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 near Grand Forks: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 19, 30% May 16, 40% May 12, 50% May 10, 60% May 7, 70% May 4, 80% May 1, 90% April 28. Observed last spring frost in recent years: 2021 May 10, 2022 May 21, 2023 May 2, 2024 April 24, 2025 April 29, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 24May 10Apr 282021: May 102022: May 212023: May 22024: April 242025: April 292026: May 10Fall near Grand Forks: chance of a frost before this dateFall, chance of a frost before the date: 10% September 20, 20% September 24, 30% September 26, 40% September 29, 50% October 1, 60% October 3, 70% October 6, 80% October 10, 90% October 15. Observed first fall frost in recent years: 2021 October 20, 2022 October 6, 2023 October 10, 2024 October 15, 2025 October 14.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 20Oct 1Oct 152021: October 202022: October 62023: October 102024: October 152025: October 14
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 10October 20
2022May 21October 6
2023May 2October 10
2024April 24October 15
2025April 29October 14
2026May 10season not over yet

What these dates mean

The 144 days between the 50% dates in the Grand Forks area define the average frost-free season, spanning from the median light-frost date of May 10 to the median light-frost date of October 1. Within that interval, tender crops generally face a lower than even chance of a light frost.

The median dates are not frost dates; they simply mark the point at which a light frost is as likely as not. For a cautious spring plan, the 10 % chance date of May 24 is used to set out tender crops, while a cautious fall plan uses the 10 % chance date of September 20 to finish harvesting those crops. Planting on April 28 or counting on crops until October 15 would be a gamble because each carries a 90 % chance of frost.

A hard frost at 28 °F, indicated by the median dates of April 30 (spring) and October 12 (fall), can damage plant tissue that would survive a light frost at 32 °F, making it a more severe threat.

How to read the probabilities

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

  • Spring: "10% after May 24" 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 20" 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, NDNumbered nearest stations: 1 — Grand Forks (Airport), ND — 4 mi; 2 — near Crookston, MN — 24 mi; 3 — Argyle, MN — 31 mi; 4 — Red Lake Falls, MN — 38 mi; 5 — Petersburg, ND — 43 mi.NDMN25 mi · 40 km1. Grand Forks (Airport), ND — 4 mi12. near Crookston, MN — 24 mi23. Argyle, MN — 31 mi34. Red Lake Falls, MN — 38 mi45. Petersburg, ND — 43 mi5
  1. Grand Forks (Airport), ND 4 mi (7 km)
  2. near Crookston, MN 24 mi (38 km)
  3. Argyle, MN 31 mi (50 km)
  4. Red Lake Falls, MN 38 mi (61 km)
  5. Petersburg, ND 43 mi (69 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: 47.9217, -97.0975.