U.S. Frost Dates by Weather Station

NOAA station USC00248324 · Montana

Frost Dates for Townsend, MT

NOAA weather station Townsend 3 SE (USC00248324), Montana · elevation 3964 ft (1208 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 2only 1 spring in 10 still has a frost later
  • Typical last frostMay 1950% chance of a frost after it
  • Typical first fall frostSeptember 1950% chance of a frost before it
  • Frost-free season122 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Townsend, MTSpring: a frost after May 8 in 9 years out of 10, after May 19 in half of the years, after June 2 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 19 in half of the years, before October 2 in 9 years out of 10. Typical frost-free season: 122 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 19First frost ~Sep 19Frost season at Townsend, MTSpring: a frost after May 8 in 9 years out of 10, after May 19 in half of the years, after June 2 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 19 in half of the years, before October 2 in 9 years out of 10. Typical frost-free season: 122 days.JFMAMJJASONDLast frost ~May 19First frost ~Sep 19
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)June 2September 5
50% (typical)May 19September 19
90% (likely)May 8October 2
Frost-free season (32°F, 50% chance)
122 days
Hard frost (28°F), last in spring, 50% chance after
May 7
Hard frost (28°F), first in fall, 50% chance before
October 1

The last 15 years (2006–2020 normals)

Typical last frost May 19 (same as the 30-year normal), typical first fall frost September 21 (2 days later). Frost-free season 123 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 Townsend: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 2, 20% May 28, 30% May 25, 40% May 22, 50% May 19, 60% May 16, 70% May 14, 80% May 11, 90% May 8. Observed last spring frost in recent years: 2021 May 29, 2022 May 23, 2023 April 29, 2024 May 31, 2026 June 8.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 2May 19May 82021: May 292022: May 232023: April 292024: May 312026: June 8Fall at Townsend: chance of a frost before this dateFall, chance of a frost before the date: 10% September 5, 20% September 10, 30% September 14, 40% September 17, 50% September 19, 60% September 22, 70% September 25, 80% September 29, 90% October 2. Observed first fall frost in recent years: 2022 September 10, 2023 October 14, 2024 September 30, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 5Sep 19Oct 22022: September 102023: October 142024: 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
2021May 29incomplete record
2022May 23September 10
2023April 29October 14
2024May 31September 30
2025incomplete recordOctober 6
2026June 8season not over yet

What these dates mean

June 2 is the cautious spring date, with only a 10 % chance of a light frost later; gardeners can use it as the earliest reliable day to set out tender crops. The earlier May 8 date carries a 90 % chance of frost and is a gamble, while the median May 19 date marks the point at which the odds of a frost later are even.

In fall, September 5 is the cautious date, offering a 10 % chance that a light frost has arrived earlier, making it the latest sensible day to finish harvesting tender crops. The October 2 date is a gamble with a 90 % chance of frost already occurring, and the median September 19 date represents even odds for a frost earlier. The hard-frost 50 % dates are May 7 in spring and October 1 in fall; a hard frost at 28 °F can damage plant tissue that survives 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 2" 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 5" 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 Townsend, MTNumbered nearest stations: 1 — Trident, MT — 24 mi; 2 — Boulder, MT — 32 mi; 3 — Helena, MT — 32 mi; 4 — Bozeman (Gallatin Field), MT — 38 mi; 5 — Millegan, MT — 42 mi.25 mi · 40 km1. Trident, MT — 24 mi12. Boulder, MT — 32 mi23. Helena, MT — 32 mi34. Bozeman (Gallatin Field), MT — 38 mi45. Millegan, MT — 42 mi5
  1. Trident, MT 24 mi (39 km)
  2. Boulder, MT 32 mi (51 km)
  3. Helena, MT 32 mi (52 km)
  4. Bozeman (Gallatin Field), MT 38 mi (61 km)
  5. Millegan, MT 42 mi (68 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 46.2989, -111.4525.