U.S. Frost Dates by Weather Station

NOAA station USW00094012 · Montana

Frost Dates for Havre, MT

NOAA weather station Havre City County Airport (USW00094012), Montana · elevation 2585 ft (788 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 27only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostSeptember 2350% chance of a frost before it
  • Frost-free season129 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Havre, MTSpring: a frost after May 3 in 9 years out of 10, after May 15 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 11 in 1 year out of 10, before September 23 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 129 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 23Frost season at Havre, MTSpring: a frost after May 3 in 9 years out of 10, after May 15 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 11 in 1 year out of 10, before September 23 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 129 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 23
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)May 27September 11
50% (typical)May 15September 23
90% (likely)May 3October 5
Frost-free season (32°F, 50% chance)
129 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 1

The last 15 years (2006–2020 normals)

Typical last frost May 15 (same as the 30-year normal), typical first fall frost September 28 (5 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 Havre: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 27, 20% May 24, 30% May 20, 40% May 17, 50% May 15, 60% May 13, 70% May 11, 80% May 8, 90% May 3. Observed last spring frost in recent years: 2021 May 22, 2022 June 2, 2023 April 28, 2024 May 20, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 27May 15May 32021: May 222022: June 22023: April 282024: May 202026: May 22Fall at Havre: chance of a frost before this dateFall, chance of a frost before the date: 10% September 11, 20% September 16, 30% September 19, 40% September 21, 50% September 23, 60% September 26, 70% September 28, 80% October 1, 90% October 5. Observed first fall frost in recent years: 2021 September 17, 2022 September 21, 2023 October 5, 2024 October 3, 2025 October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 11Sep 23Oct 52021: September 172022: September 212023: October 52024: October 32025: October 5
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 22September 17
2022June 2September 21
2023April 28October 5
2024May 20October 3
2025incomplete recordOctober 5
2026May 22season not over yet

What these dates mean

Setting out tender crops on the early spring date of May 3 in Havre is a gamble, because there is a 90 % chance of a frost later than that day.

The 50 % dates mark the point where a light frost (32 °F) is equally likely to occur later (spring) or earlier (fall). In Havre the median light-frost dates are May 15 and September 23, each representing an even-odds scenario. Gardeners who prefer a lower risk schedule planting after the cautious spring date of May 27 and aim to finish tender crops before the cautious fall date of September 11.

A hard frost at 28 °F, such as the median dates of May 3 and October 1, can injure plants that would survive the milder 32 °F light frost, making it a more serious 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 27" 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 11" 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 Havre, MTNumbered nearest stations: 1 — Fort Assiniboine, MT — 4 mi; 2 — Gildford, MT — 25 mi; 3 — Chinook, MT — 25 mi; 4 — Simpson 6 N - Wildhorse, MT — 38 mi; 5 — Loma, MT — 54 mi.25 mi · 40 km1. Fort Assiniboine, MT — 4 mi12. Gildford, MT — 25 mi23. Chinook, MT — 25 mi34. Simpson 6 N - Wildhorse, MT — 38 mi45. Loma, MT — 54 mi5
  1. Fort Assiniboine, MT 4 mi (6 km)
  2. Gildford, MT 25 mi (40 km)
  3. Chinook, MT 25 mi (40 km)
  4. Simpson 6 N - Wildhorse, MT 38 mi (61 km)
  5. Loma, MT 54 mi (87 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: 48.5428, -109.7633.