U.S. Frost Dates by Weather Station

NOAA station USC00247382 · Montana

Frost Dates for Savage, MT

NOAA weather station Savage (USC00247382), Montana · elevation 1978 ft (603 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 26only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostSeptember 2550% chance of a frost before it
  • Frost-free season135 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Savage, MTSpring: a frost after May 1 in 9 years out of 10, after May 12 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 25 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 135 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Sep 25Frost season at Savage, MTSpring: a frost after May 1 in 9 years out of 10, after May 12 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 25 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 135 days.JFMAMJJASONDLast frost ~May 12First frost ~Sep 25
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 26September 12
50% (typical)May 12September 25
90% (likely)May 1October 8
Frost-free season (32°F, 50% chance)
135 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 11 (1 day earlier than the 30-year normal), typical first fall frost September 30 (5 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 Savage: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 21, 30% May 17, 40% May 15, 50% May 12, 60% May 10, 70% May 7, 80% May 4, 90% May 1. Observed last spring frost in recent years: 2021 May 11, 2022 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 12May 12021: May 112022: May 22Fall at Savage: chance of a frost before this dateFall, chance of a frost before the date: 10% September 12, 20% September 18, 30% September 21, 40% September 24, 50% September 25, 60% September 28, 70% September 30, 80% October 3, 90% October 8. Observed first fall frost in recent years: 2021 October 13.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 12Sep 25Oct 82021: October 13
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 13
2022May 22incomplete record
2023incomplete recordno data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

The cautious fall date for finishing the harvest in Savage is September 12, when there is only a 10% chance that a light frost has already occurred. The median 50% date is September 25, meaning a gardener faces even odds of a frost earlier than that day, and the gamble date of October 8 carries a 90% chance of a frost arriving before the harvest is complete.

In spring the cautious date for setting out tender crops is May 26, with a 10% chance of a light frost later in the season. The 50% median date is May 12, while planting on May 1 involves a 90% chance of a frost later that season. Hard frost at 28°F is noted on May 3 in spring and October 4 in fall; it matters more than a light frost because it can kill plants that would otherwise survive a 32°F chill.

How to read the probabilities

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

  • Spring: "10% after May 26" 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 12" 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 Savage, MTNumbered nearest stations: 1 — Sidney, MT — 21 mi; 2 — Glendive, MT — 30 mi; 3 — Culbertson, MT — 49 mi; 4 — Carlyle, MT — 49 mi; 5 — Grassy Butte, ND — 53 mi.MT25 mi · 40 km1. Sidney, MT — 21 mi12. Glendive, MT — 30 mi23. Culbertson, MT — 49 mi34. Carlyle, MT — 49 mi45. Grassy Butte, ND — 53 mi5
  1. Sidney, MT 21 mi (34 km)
  2. Glendive, MT 30 mi (48 km)
  3. Culbertson, MT 49 mi (79 km)
  4. Carlyle, MT 49 mi (79 km)
  5. Grassy Butte, ND 53 mi (85 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: 47.4536, -104.3378.