U.S. Frost Dates by Weather Station

NOAA station USW00024037 · Montana

Frost Dates near Miles City, MT

NOAA weather station Miles City F Wiley Field (USW00024037), Montana · elevation 2624 ft (800 m) · hardiness zone 4b*

Miles City is the nearest town to the station (2.4 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 850% chance of a frost after it
  • Typical first fall frostSeptember 3050% chance of a frost before it
  • Frost-free season144 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season near Miles City, MTSpring: a frost after April 26 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before September 30 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 144 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 8First frost ~Sep 30Frost season near Miles City, MTSpring: a frost after April 26 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before September 30 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 144 days.JFMAMJJASONDLast frost ~May 8First frost ~Sep 30
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 21September 17
50% (typical)May 8September 30
90% (likely)April 26October 14
Frost-free season (32°F, 50% chance)
144 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 8

The last 15 years (2006–2020 normals)

Typical last frost May 7 (1 day earlier than the 30-year normal), typical first fall frost October 2 (2 days later). Frost-free season 146 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 near Miles City: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 17, 30% May 13, 40% May 10, 50% May 8, 60% May 5, 70% May 3, 80% April 30, 90% April 26. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 April 24, 2024 May 4, 2025 April 23, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 8Apr 262021: May 112022: May 222023: April 242024: May 42025: April 232026: May 19Fall near Miles City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 22, 30% September 26, 40% September 28, 50% September 30, 60% October 2, 70% October 5, 80% October 9, 90% October 14. Observed first fall frost in recent years: 2021 October 11, 2022 October 16, 2023 October 6, 2024 October 23, 2025 October 21.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Sep 30Oct 142021: October 112022: October 162023: October 62024: October 232025: October 21
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 11
2022May 22October 16
2023April 24October 6
2024May 4October 23
2025April 23October 21
2026May 19season not over yet

What these dates mean

May 21 is the cautious spring date for the Miles City area, marking a 10 % chance that a light frost will occur later; this lets a gardener schedule the earliest planting of tender crops with minimal frost risk.

The 50% spring date, May 8, indicates an even odds of a light frost later than this date, while the 50% fall date, September 30, shows a 50 % chance of a light frost earlier than this date. For a conservative schedule, the cautious fall date is September 17, which carries only a 10 % chance that a light frost has already arrived, providing a reliable point to finish harvesting tender crops. The hard-frost median dates are April 29 in spring and October 8 in fall.

Because a hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F, it is a more critical threshold for gardeners in this region.

How to read the probabilities

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

  • Spring: "10% after May 21" 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 17" 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 Miles City, MTNumbered nearest stations: 1 — Mizpah, MT — 30 mi; 2 — Terry, MT — 37 mi; 3 — Forsyth, MT — 39 mi; 4 — Brandenberg, MT — 45 mi; 5 — Mildred, MT — 49 mi.MT25 mi · 40 km1. Mizpah, MT — 30 mi12. Terry, MT — 37 mi23. Forsyth, MT — 39 mi34. Brandenberg, MT — 45 mi45. Mildred, MT — 49 mi5
  1. Mizpah, MT 30 mi (48 km)
  2. Terry, MT 37 mi (60 km)
  3. Forsyth, MT 39 mi (63 km)
  4. Brandenberg, MT 45 mi (73 km)
  5. Mildred, MT 49 mi (80 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: 46.4267, -105.8825.