U.S. Frost Dates by Weather Station

NOAA station USW00024132 · Montana

Frost Dates for Bozeman (Gallatin Field), MT

NOAA weather station Bozeman Gallatin Field (USW00024132), Montana · elevation 4427 ft (1349 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 12only 1 spring in 10 still has a frost later
  • Typical last frostMay 2650% chance of a frost after it
  • Typical first fall frostSeptember 1650% chance of a frost before it
  • Frost-free season112 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Bozeman (Gallatin Field), MTSpring: a frost after May 11 in 9 years out of 10, after May 26 in half of the years, after June 12 in 1 year out of 10. Fall: the first frost comes before September 2 in 1 year out of 10, before September 16 in half of the years, before September 29 in 9 years out of 10. Typical frost-free season: 112 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 26First frost ~Sep 16Frost season at Bozeman (Gallatin Field), MTSpring: a frost after May 11 in 9 years out of 10, after May 26 in half of the years, after June 12 in 1 year out of 10. Fall: the first frost comes before September 2 in 1 year out of 10, before September 16 in half of the years, before September 29 in 9 years out of 10. Typical frost-free season: 112 days.JFMAMJJASONDLast frost ~May 26First frost ~Sep 16
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 12September 2
50% (typical)May 26September 16
90% (likely)May 11September 29
Frost-free season (32°F, 50% chance)
112 days
Hard frost (28°F), last in spring, 50% chance after
May 9
Hard frost (28°F), first in fall, 50% chance before
September 28

The last 15 years (2006–2020 normals)

Typical last frost May 25 (1 day earlier than the 30-year normal), typical first fall frost September 19 (3 days later). Frost-free season 116 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 Bozeman (Gallatin Field): chance of a frost after this dateSpring, chance of a frost after the date: 10% June 12, 20% June 5, 30% June 2, 40% May 29, 50% May 26, 60% May 23, 70% May 20, 80% May 16, 90% May 11. Observed last spring frost in recent years: 2021 June 11, 2022 May 23, 2023 May 10, 2024 May 31, 2025 May 21, 2026 June 8.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 12May 26May 112021: June 112022: May 232023: May 102024: May 312025: May 212026: June 8Fall at Bozeman (Gallatin Field): chance of a frost before this dateFall, chance of a frost before the date: 10% September 2, 20% September 6, 30% September 10, 40% September 12, 50% September 16, 60% September 19, 70% September 21, 80% September 24, 90% September 29. Observed first fall frost in recent years: 2021 September 17, 2022 September 10, 2023 October 7, 2024 September 22, 2025 September 27.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 2Sep 16Sep 292021: September 172022: September 102023: October 72024: September 222025: September 27
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
2021June 11September 17
2022May 23September 10
2023May 10October 7
2024May 31September 22
2025May 21September 27
2026June 8season not over yet

What these dates mean

The cautious fall date for finishing the harvest in Bozeman is September 2, when there is only a 10 % chance that a light frost has arrived.

For tender crops in spring, the cautious date is June 12, which carries a 10 % chance of a light frost occurring later. The 50% date for light frost in spring is May 26, and the 50% date in fall is September 16. Planting before May 11 is a gamble because that date has a 90 % chance of a frost later.

Hard frosts at 28 °F are more damaging than light frosts at 32 °F; the 50% hard-frost dates are May 9 in spring and September 28 in fall, marking the median risk for severe freezing. The climate record spans 28 years, and the span between the two 32 °F 50% dates is 112 days.

How to read the probabilities

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

  • Spring: "10% after June 12" 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 2" 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 Bozeman (Gallatin Field), MTNumbered nearest stations: 1 — near Four Corners, MT — 8 mi; 2 — near Bozeman, MT — 10 mi; 3 — Trident, MT — 19 mi; 4 — Norris Madison Power House, MT — 31 mi; 5 — Townsend, MT — 38 mi.25 mi · 40 km1. near Four Corners, MT — 8 mi12. near Bozeman, MT — 10 mi23. Trident, MT — 19 mi34. Norris Madison Power House, MT — 31 mi45. Townsend, MT — 38 mi5
  1. near Four Corners, MT 8 mi (13 km)
  2. near Bozeman, MT 10 mi (17 km)
  3. Trident, MT 19 mi (30 km)
  4. Norris Madison Power House, MT 31 mi (50 km)
  5. Townsend, MT 38 mi (61 km)

Sources

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

Station coordinates: 45.7881, -111.1608.