U.S. Frost Dates by Weather Station

NOAA station USC00248415 · Montana

Frost Dates for Turner, MT

NOAA weather station Turner 11 N (USC00248415), Montana · elevation 2982 ft (909 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 1950% chance of a frost after it
  • Typical first fall frostSeptember 2150% chance of a frost before it
  • Frost-free season124 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Turner, MTSpring: a frost after May 7 in 9 years out of 10, after May 19 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 21 in half of the years, before October 2 in 9 years out of 10. Typical frost-free season: 124 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 19First frost ~Sep 21Frost season at Turner, MTSpring: a frost after May 7 in 9 years out of 10, after May 19 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 21 in half of the years, before October 2 in 9 years out of 10. Typical frost-free season: 124 days.JFMAMJJASONDLast frost ~May 19First 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 8
50% (typical)May 19September 21
90% (likely)May 7October 2
Frost-free season (32°F, 50% chance)
124 days
Hard frost (28°F), last in spring, 50% chance after
May 9
Hard frost (28°F), first in fall, 50% chance before
September 30

The last 15 years (2006–2020 normals)

Typical last frost May 20 (1 day later than the 30-year normal), typical first fall frost September 24 (3 days later). Frost-free season 128 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 Turner: 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 22, 50% May 19, 60% May 17, 70% May 14, 80% May 11, 90% May 7. Observed last spring frost in recent years: 2022 May 23, 2024 May 3, 2025 May 6, 2026 May 21.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 19May 72022: May 232024: May 32025: May 62026: May 21Fall at Turner: chance of a frost before this dateFall, chance of a frost before the date: 10% September 8, 20% September 13, 30% September 17, 40% September 19, 50% September 21, 60% September 24, 70% September 26, 80% September 29, 90% October 2. Observed first fall frost in recent years: 2021 September 17, 2022 September 21, 2023 October 6, 2024 October 3, 2025 October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 8Sep 21Oct 22021: September 172022: September 212023: October 62024: 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
2021incomplete recordSeptember 17
2022May 23September 21
2023incomplete recordOctober 6
2024May 3October 3
2025May 6October 5
2026May 21season not over yet

What these dates mean

Setting out tender crops on May 7 in Turner carries a 90% chance of a frost later than the date, making it a gamble for early planting. The 50% date is May 19, a 50% chance of a frost later than this date, while the cautious spring date is June 1, when the chance of a later frost drops to 10%.

The 50% date is September 21, a 50% chance of a frost earlier than this date. For finishing harvest of tender crops, the cautious fall date is September 8, with only a 10% chance that a frost has arrived earlier, whereas waiting until October 2 would involve a 90% chance of an earlier frost.

Hard frosts at 28°F are more damaging than light frosts at 32°F because the lower temperature can kill plant tissues that survive a milder freeze.

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 8" 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 Turner, MTNumbered nearest stations: 1 — Chinook, MT — 48 mi; 2 — Saco, MT — 60 mi; 3 — Havre, MT — 70 mi; 4 — Fort Assiniboine, MT — 73 mi; 5 — Content, MT — 75 mi.MT25 mi · 40 km1. Chinook, MT — 48 mi12. Saco, MT — 60 mi23. Havre, MT — 70 mi34. Fort Assiniboine, MT — 73 mi45. Content, MT — 75 mi5
  1. Chinook, MT 48 mi (76 km)
  2. Saco, MT 60 mi (96 km)
  3. Havre, MT 70 mi (113 km)
  4. Fort Assiniboine, MT 73 mi (118 km)
  5. Content, MT 75 mi (120 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: 48.9992, -108.3894.