U.S. Frost Dates by Weather Station

NOAA station USC00241088 · Montana

Frost Dates for Bredette, MT

NOAA weather station Bredette (USC00241088), Montana · elevation 2313 ft (705 m) · hardiness zone 3b*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostSeptember 2150% chance of a frost before it
  • Frost-free season122 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Bredette, MTSpring: a frost after May 8 in 9 years out of 10, after May 20 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 21 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 122 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Sep 21Frost season at Bredette, MTSpring: a frost after May 8 in 9 years out of 10, after May 20 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 21 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 122 days.JFMAMJJASONDLast frost ~May 20First frost ~Sep 21
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)June 1September 6
50% (typical)May 20September 21
90% (likely)May 8October 1
Frost-free season (32°F, 50% chance)
122 days
Hard frost (28°F), last in spring, 50% chance after
May 10
Hard frost (28°F), first in fall, 50% chance before
September 28

The last 15 years (2006–2020 normals)

Typical last frost May 19 (1 day earlier than the 30-year normal), typical first fall frost September 21. Frost-free season 122 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 Bredette: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 28, 30% May 25, 40% May 23, 50% May 20, 60% May 18, 70% May 15, 80% May 12, 90% May 8. Observed last spring frost in recent years: 2021 May 11, 2023 April 24, 2024 April 20, 2025 May 22, 2026 May 5.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 20May 82021: May 112023: April 242024: April 202025: May 222026: May 5Fall at Bredette: chance of a frost before this dateFall, chance of a frost before the date: 10% September 6, 20% September 11, 30% September 16, 40% September 19, 50% September 21, 60% September 23, 70% September 25, 80% September 28, 90% October 1. Observed first fall frost in recent years: 2021 September 17, 2022 September 22, 2023 October 6, 2024 October 1, 2025 October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 6Sep 21Oct 12021: September 172022: September 222023: October 62024: October 12025: 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 11September 17
2022incomplete recordSeptember 22
2023April 24October 6
2024April 20October 1
2025May 22October 5
2026May 5season not over yet

What these dates mean

June 1 is the cautious spring date, giving a gardener only a 10% chance of a light frost later and thus allowing tender crops to be set out with minimal risk. The 50% date in spring is May 20, marking the point where a light frost is equally likely to occur later as not.

September 6 is the cautious fall date, meaning there is only a 10% chance that a light frost has arrived earlier, so it is the latest reliable day to finish harvesting tender crops. The 50% date in fall is September 21, indicating an even odds frost chance. May 10 and September 28 are the 50% dates for hard frost, and a hard frost at 28 °F can damage plants more severely than 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 June 1" 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 6" 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 Bredette, MTNumbered nearest stations: 1 — Scobey, MT — 24 mi; 2 — Vida, MT — 44 mi; 3 — Culbertson, MT — 44 mi; 4 — Opheim, MT — 48 mi; 5 — Fort Peck Power Plant, MT — 62 mi.MT25 mi · 40 km1. Scobey, MT — 24 mi12. Vida, MT — 44 mi23. Culbertson, MT — 44 mi34. Opheim, MT — 48 mi45. Fort Peck Power Plant, MT — 62 mi5
  1. Scobey, MT 24 mi (38 km)
  2. Vida, MT 44 mi (71 km)
  3. Culbertson, MT 44 mi (71 km)
  4. Opheim, MT 48 mi (77 km)
  5. Fort Peck Power Plant, MT 62 mi (100 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: 48.5156, -105.2992.