U.S. Frost Dates by Weather Station

NOAA station USC00321408 · North Dakota

Frost Dates near Casselton, ND

NOAA weather station Casselton Agronomy Farm (USC00321408), North Dakota · elevation 935 ft (285 m) · hardiness zone 4a*

Casselton is the nearest town to the station (1.9 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 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 950% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season near Casselton, NDSpring: a frost after April 25 in 9 years out of 10, after May 9 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 17 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: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 9First frost ~Oct 1Frost season near Casselton, NDSpring: a frost after April 25 in 9 years out of 10, after May 9 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 17 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: 143 days.JFMAMJJASONDLast frost ~May 9First 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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 21September 17
50% (typical)May 9October 1
90% (likely)April 25October 15
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 8 (1 day earlier than the 30-year normal), typical first fall frost October 5 (4 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 Casselton: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 17, 30% May 14, 40% May 11, 50% May 9, 60% May 5, 70% May 3, 80% April 30, 90% April 25. Observed last spring frost in recent years: 2021 May 28, 2022 May 21, 2023 April 27, 2024 April 25, 2025 April 30, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 9Apr 252021: May 282022: May 212023: April 272024: April 252025: April 302026: May 20Fall near Casselton: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 22, 30% September 26, 40% September 29, 50% October 1, 60% October 3, 70% October 6, 80% October 9, 90% October 15. Observed first fall frost in recent years: 2021 October 17, 2022 October 7, 2023 October 7, 2024 October 15, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Oct 1Oct 152021: October 172022: October 72023: October 72024: October 152025: 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 28October 17
2022May 21October 7
2023April 27October 7
2024April 25October 15
2025April 30October 8
2026May 20season not over yet

What these dates mean

May 21 marks the cautious spring date for the Casselton area, with only a 10 % chance of a light frost later, and it lets a gardener set out tender crops with confidence. The early gamble date of April 25 carries a 90 % chance of frost, so planting before May 21 is risky.

The 50 % dates—May 9 for spring and October 1 for fall—represent the median point where a light frost is equally likely to occur later (spring) or earlier (fall). A gardener can use these dates as a reference for the even-odds boundary. The cautious fall date is September 17, with a 10 % chance of a light frost earlier, guiding the latest appropriate time to finish harvesting tender crops. The 28°F hard-frost 50 % dates are April 29 and October 10.

A hard frost at 28°F can damage plant tissue that survives a light frost at 32°F.

How to read the probabilities

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

  • Spring: "10% after May 21" 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 17" 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 Casselton, NDNumbered nearest stations: 1 — near Fargo, ND — 20 mi; 2 — Georgetown, MN — 26 mi; 3 — McLeod, ND — 34 mi; 4 — Rothsay, MN — 53 mi; 5 — Forman, ND — 61 mi.NDMN25 mi · 40 km1. near Fargo, ND — 20 mi12. Georgetown, MN — 26 mi23. McLeod, ND — 34 mi34. Rothsay, MN — 53 mi45. Forman, ND — 61 mi5
  1. near Fargo, ND 20 mi (32 km)
  2. Georgetown, MN 26 mi (41 km)
  3. McLeod, ND 34 mi (54 km)
  4. Rothsay, MN 53 mi (85 km)
  5. Forman, ND 61 mi (98 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: 46.8769, -97.2328.