U.S. Frost Dates by Weather Station

NOAA station USC00248165 · Montana

Frost Dates for Terry, MT

NOAA weather station Terry (USC00248165), Montana · elevation 2250 ft (686 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Terry, MTSpring: a frost after April 30 in 9 years out of 10, after May 12 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 28 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Sep 28Frost season at Terry, MTSpring: a frost after April 30 in 9 years out of 10, after May 12 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 28 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 137 days.JFMAMJJASONDLast frost ~May 12First frost ~Sep 28
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)May 25September 13
50% (typical)May 12September 28
90% (likely)April 30October 9
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 12 (same as the 30-year normal), typical first fall frost September 30 (2 days later). Frost-free season 140 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 Terry: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 20, 30% May 17, 40% May 15, 50% May 12, 60% May 10, 70% May 7, 80% May 4, 90% April 30. Observed last spring frost in recent years: 2021 May 11, 2022 May 23, 2023 April 30, 2024 May 4, 2025 May 2, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 12Apr 302021: May 112022: May 232023: April 302024: May 42025: May 22026: May 19Fall at Terry: chance of a frost before this dateFall, chance of a frost before the date: 10% September 13, 20% September 19, 30% September 22, 40% September 25, 50% September 28, 60% October 1, 70% October 3, 80% October 5, 90% October 9. Observed first fall frost in recent years: 2021 October 1, 2022 October 8, 2023 October 6, 2024 October 1, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 13Sep 28Oct 92021: October 12022: October 82023: October 62024: October 12025: 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
2021May 11October 1
2022May 23October 8
2023April 30October 6
2024May 4October 1
2025May 2October 6
2026May 19season not over yet

What these dates mean

Planting tender crops on April 30 in Terry carries a 90 % chance of a light frost later, so doing so is a gamble. The early-spring date is the one with the high risk, while the cautious spring date for setting out tender crops is May 25, when only a 10 % chance of a later frost remains.

The 50 % spring date, May 12, marks the point at which a light frost is equally likely to occur later or not, and the 50 % fall date, September 28, marks the same even odds for a frost occurring earlier. Gardeners who prefer a lower risk follow the cautious dates—May 25 for planting and September 13 for finishing tender crops—because each carries only a 10 % chance of a light frost crossing the threshold.

A hard frost, recorded at 28 °F, is more critical than a light frost because it can damage or kill plants that survive 32 °F; the median hard-frost dates are May 1 in spring and October 5 in fall.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 13" 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 Terry, MTNumbered nearest stations: 1 — Mildred, MT — 16 mi; 2 — Glendive, MT — 35 mi; 3 — Mizpah, MT — 35 mi; 4 — near Miles City, MT — 37 mi; 5 — Brockway, MT — 42 mi.MTND25 mi · 40 km1. Mildred, MT — 16 mi12. Glendive, MT — 35 mi23. Mizpah, MT — 35 mi34. near Miles City, MT — 37 mi45. Brockway, MT — 42 mi5
  1. Mildred, MT 16 mi (26 km)
  2. Glendive, MT 35 mi (56 km)
  3. Mizpah, MT 35 mi (57 km)
  4. near Miles City, MT 37 mi (60 km)
  5. Brockway, MT 42 mi (68 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: 46.7939, -105.3022.