U.S. Frost Dates by Weather Station

NOAA station USC00243581 · Montana

Frost Dates for Glendive, MT

NOAA weather station Glendive (USC00243581), Montana · elevation 2075 ft (633 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season153 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Glendive, MTSpring: a frost after April 19 in 9 years out of 10, after May 3 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 4 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 153 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 4Frost season at Glendive, MTSpring: a frost after April 19 in 9 years out of 10, after May 3 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 4 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 153 days.JFMAMJJASONDLast frost ~May 3First frost ~Oct 4
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 16September 22
50% (typical)May 3October 4
90% (likely)April 19October 17
Frost-free season (32°F, 50% chance)
153 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 13

The last 15 years (2006–2020 normals)

Typical last frost May 4 (1 day later than the 30-year normal), typical first fall frost October 4. Frost-free season 153 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 Glendive: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 12, 30% May 8, 40% May 6, 50% May 3, 60% May 1, 70% April 29, 80% April 24, 90% April 19. Observed last spring frost in recent years: 2022 May 22, 2023 May 1, 2024 May 5, 2025 April 24, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 3Apr 192022: May 222023: May 12024: May 52025: April 242026: May 7Fall at Glendive: chance of a frost before this dateFall, chance of a frost before the date: 10% September 22, 20% September 26, 30% September 29, 40% October 1, 50% October 4, 60% October 7, 70% October 10, 80% October 13, 90% October 17. Observed first fall frost in recent years: 2021 October 13, 2022 October 7, 2023 October 6, 2024 October 13, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 22Oct 4Oct 172021: October 132022: October 72023: October 62024: October 132025: 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
2021incomplete recordOctober 13
2022May 22October 7
2023May 1October 6
2024May 5October 13
2025April 24October 6
2026May 7season not over yet

What these dates mean

September 22 is the cautious fall date in Glendive for finishing the harvest, because there is only a 10% chance that a light frost has arrived earlier.

For tender crops the cautious spring date is May 16, when the chance of a light frost later is just 10%; planting before April 19 would be a gamble with a 90% chance of frost. The 50% date for spring light frost is May 3, meaning there is a 50% chance of a frost later than that date, and the 50% date for fall light frost is October 4, meaning there is a 50% chance of a frost earlier than that date.

A hard frost at 28°F can cause far greater damage than a light frost at 32°F, so the median hard-frost dates of April 24 in spring and October 13 in fall mark when that higher risk becomes even.

How to read the probabilities

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

  • Spring: "10% after May 16" 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 22" 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 Glendive, MTNumbered nearest stations: 1 — Mildred, MT — 26 mi; 2 — Savage, MT — 30 mi; 3 — Carlyle, MT — 32 mi; 4 — Terry, MT — 35 mi; 5 — Circle, MT — 46 mi.MTND25 mi · 40 km1. Mildred, MT — 26 mi12. Savage, MT — 30 mi23. Carlyle, MT — 32 mi34. Terry, MT — 35 mi45. Circle, MT — 46 mi5
  1. Mildred, MT 26 mi (43 km)
  2. Savage, MT 30 mi (48 km)
  3. Carlyle, MT 32 mi (51 km)
  4. Terry, MT 35 mi (56 km)
  5. Circle, MT 46 mi (75 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: 47.1058, -104.7175.