U.S. Frost Dates by Weather Station

NOAA station USC00218254 · Minnesota

Frost Dates for Thorhult, MN

NOAA weather station Thorhult (USC00218254), Minnesota · elevation 1237 ft (377 m) · hardiness zone 3b*

  • Lower-risk planting dateafter June 7only 1 spring in 10 still has a frost later
  • Typical last frostMay 2450% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season120 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Thorhult, MNSpring: a frost after May 7 in 9 years out of 10, after May 24 in half of the years, after June 7 in 1 year out of 10. Fall: the first frost comes before September 4 in 1 year out of 10, before September 20 in half of the years, before October 3 in 9 years out of 10. Typical frost-free season: 120 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 24First frost ~Sep 20Frost season at Thorhult, MNSpring: a frost after May 7 in 9 years out of 10, after May 24 in half of the years, after June 7 in 1 year out of 10. Fall: the first frost comes before September 4 in 1 year out of 10, before September 20 in half of the years, before October 3 in 9 years out of 10. Typical frost-free season: 120 days.JFMAMJJASONDLast frost ~May 24First frost ~Sep 20
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 7September 4
50% (typical)May 24September 20
90% (likely)May 7October 3
Frost-free season (32°F, 50% chance)
120 days
Hard frost (28°F), last in spring, 50% chance after
May 12
Hard frost (28°F), first in fall, 50% chance before
October 1

The last 15 years (2006–2020 normals)

Typical last frost May 24 (same as the 30-year normal), typical first fall frost September 21 (1 day later). Frost-free season 118 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 Thorhult: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 7, 20% June 2, 30% May 30, 40% May 27, 50% May 24, 60% May 21, 70% May 17, 80% May 13, 90% May 7. Observed last spring frost in recent years: 2021 May 28, 2022 May 22, 2023 May 3, 2024 May 5, 2025 April 29.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 7May 24May 72021: May 282022: May 222023: May 32024: May 52025: April 29Fall at Thorhult: chance of a frost before this dateFall, chance of a frost before the date: 10% September 4, 20% September 9, 30% September 14, 40% September 18, 50% September 20, 60% September 23, 70% September 26, 80% September 30, 90% October 3. Observed first fall frost in recent years: 2021 October 16, 2022 September 27, 2023 October 8, 2024 October 4, 2025 September 7.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 4Sep 20Oct 32021: October 162022: September 272023: October 82024: October 42025: 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 16
2022May 22September 27
2023May 3October 8
2024May 5October 4
2025April 29September 7
2026incomplete recordseason not over yet

What these dates mean

September 4 marks the cautious fall date in Thorhult, Minnesota, when there is only a 10 % chance that a light frost has arrived, making it the recommended day to finish harvesting tender crops.

The 50% date is May 24, which carries a 50 % chance of a light frost later than this date, and the 50% date is September 20, which carries a 50 % chance of a light frost earlier than this date; together they define the midpoint of the frost-free window. A cautious spring plan uses June 7, the date with a 10 % chance of a frost later than that day, while the cautious fall plan relies on September 4.

Hard frosts at 28 °F, with median dates of May 12 in spring and October 1 in fall, can damage plant tissue that survives a light frost, so they represent a greater risk for tender crops.

How to read the probabilities

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

  • Spring: "10% after June 7" 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 4" 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 Thorhult, MNNumbered nearest stations: 1 — Red Lake Falls, MN — 53 mi; 2 — Cass Lake, MN — 64 mi; 3 — Itasca University of Minn, MN — 68 mi; 4 — near Crookston, MN — 69 mi; 5 — Argyle, MN — 73 mi.MNND25 mi · 40 km1. Red Lake Falls, MN — 53 mi12. Cass Lake, MN — 64 mi23. Itasca University of Minn, MN — 68 mi34. near Crookston, MN — 69 mi45. Argyle, MN — 73 mi5
  1. Red Lake Falls, MN 53 mi (85 km)
  2. Cass Lake, MN 64 mi (103 km)
  3. Itasca University of Minn, MN 68 mi (110 km)
  4. near Crookston, MN 69 mi (111 km)
  5. Argyle, MN 73 mi (118 km)

Sources

* Hardiness zone 3b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.2108, -95.2475.