U.S. Frost Dates by Weather Station

NOAA station USC00248809 · Montana

Frost Dates for West Glacier, MT

NOAA weather station West Glacier (USC00248809), Montana · elevation 3148 ft (960 m) · hardiness zone 5a*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 1850% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season124 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at West Glacier, MTSpring: a frost after May 6 in 9 years out of 10, after May 18 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 3 in 1 year out of 10, before September 20 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 124 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 18First frost ~Sep 20Frost season at West Glacier, MTSpring: a frost after May 6 in 9 years out of 10, after May 18 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 3 in 1 year out of 10, before September 20 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 124 days.JFMAMJJASONDLast frost ~May 18First 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.Today

Frost dates (32°F)

Probability of frost, based on 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 4September 3
50% (typical)May 18September 20
90% (likely)May 6October 4
Frost-free season (32°F, 50% chance)
124 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 16 (2 days earlier than the 30-year normal), typical first fall frost September 23 (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 West Glacier: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 29, 30% May 24, 40% May 21, 50% May 18, 60% May 15, 70% May 13, 80% May 10, 90% May 6. Observed last spring frost in recent years: 2021 April 21, 2022 May 23, 2023 April 29, 2024 May 31, 2025 May 22, 2026 May 18.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 18May 62021: April 212022: May 232023: April 292024: May 312025: May 222026: May 18Fall at West Glacier: chance of a frost before this dateFall, chance of a frost before the date: 10% September 3, 20% September 9, 30% September 13, 40% September 17, 50% September 20, 60% September 23, 70% September 26, 80% September 30, 90% October 4. Observed first fall frost in recent years: 2021 October 8, 2022 September 10, 2023 October 7, 2024 September 30, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 3Sep 20Oct 42021: October 82022: September 102023: October 72024: September 302025: October 6
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
2021April 21October 8
2022May 23September 10
2023April 29October 7
2024May 31September 30
2025May 22October 6
2026May 18season not over yet

What these dates mean

June 4 is the cautious spring date for light frost in West Glacier, with only a 10 % chance of a frost later than that day, and it lets gardeners set out tender crops with minimal risk. By contrast, the early spring gamble of May 6 carries a 90 % chance of frost, while the median May 18 is the 50 % date, indicating a 50 % chance of a frost later than this date.

For the autumn season, September 3 is the cautious light-frost date, with only a 10 % chance of a frost earlier than that day, providing a reliable point to finish harvesting tender crops. The median September 20 marks a 50 % chance of a frost earlier than this date, and October 4 is the high-risk gamble with a 90 % chance of frost before then. The hard-frost 50 % dates are May 1 in spring and October 4 in fall; 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 4" 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 3" 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 West Glacier, MTNumbered nearest stations: 1 — near Kalispell, MT — 19 mi; 2 — Creston, MT — 23 mi; 3 — Libby Dam (Base), MT — 61 mi; 4 — Cut Bank, MT — 74 mi; 5 — Lindbergh Lake, MT — 76 mi.MT25 mi · 40 km1. near Kalispell, MT — 19 mi12. Creston, MT — 23 mi23. Libby Dam (Base), MT — 61 mi34. Cut Bank, MT — 74 mi45. Lindbergh Lake, MT — 76 mi5
  1. near Kalispell, MT 19 mi (30 km)
  2. Creston, MT 23 mi (36 km)
  3. Libby Dam (Base), MT 61 mi (99 km)
  4. Cut Bank, MT 74 mi (119 km)
  5. Lindbergh Lake, MT 76 mi (123 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.5003, -113.9847.