U.S. Frost Dates by Weather Station

NOAA station USC00240802 · Montana

Frost Dates for Billings, MT

NOAA weather station Billings WTP (USC00240802), Montana · elevation 3097 ft (944 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season142 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Billings, MTSpring: a frost after April 26 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 142 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Oct 1Frost season at Billings, MTSpring: a frost after April 26 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 142 days.JFMAMJJASONDLast frost ~May 10First frost ~Oct 1
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 24September 19
50% (typical)May 10October 1
90% (likely)April 26October 15
Frost-free season (32°F, 50% chance)
142 days
Hard frost (28°F), last in spring, 50% chance after
April 27
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 6 (4 days earlier than the 30-year normal), typical first fall frost October 3 (2 days later). Frost-free season 148 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 Billings: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 19, 30% May 15, 40% May 12, 50% May 10, 60% May 7, 70% May 4, 80% April 30, 90% April 26. Observed last spring frost in recent years: 2021 May 22, 2022 April 30, 2023 April 28, 2024 May 4, 2025 April 29, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 24May 10Apr 262021: May 222022: April 302023: April 282024: May 42025: April 292026: May 19Fall at Billings: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 23, 30% September 26, 40% September 29, 50% October 1, 60% October 4, 70% October 6, 80% October 9, 90% October 15. Observed first fall frost in recent years: 2021 September 17, 2022 October 26, 2023 October 14, 2024 October 23, 2025 October 21.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 19Oct 1Oct 152021: September 172022: October 262023: October 142024: 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 22September 17
2022April 30October 26
2023April 28October 14
2024May 4October 23
2025April 29October 21
2026May 19season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 26 in Billings carries a 90 % chance that a light frost will occur later, making it a gamble for a gardener. The cautious spring date for tender crops is May 24, when only a 10 % chance of a later light frost remains. The 50 % date is May 10, indicating an even odds of a light frost occurring after that day.

In the fall, the cautious date to finish harvesting tender crops is September 19, when there is only a 10 % chance that a light frost has already arrived. The 50 % date is October 1, meaning an even chance of a frost occurring before that day, while the gamble date of October 15 brings a 90 % chance of an earlier frost. The 50 % hard-frost dates are April 27 and October 12; hard frosts at 28 °F can damage plant tissue more severely than light frosts 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 May 24" 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 19" 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 Billings, MTNumbered nearest stations: 1 — Billings (Logan Airport), MT — 4 mi; 2 — Columbus, MT — 39 mi; 3 — Rapelje, MT — 40 mi; 4 — Yellowtail Dam, MT — 41 mi; 5 — Hardin, MT — 42 mi.MT25 mi · 40 km1. Billings (Logan Airport), MT — 4 mi12. Columbus, MT — 39 mi23. Rapelje, MT — 40 mi34. Yellowtail Dam, MT — 41 mi45. Hardin, MT — 42 mi5
  1. Billings (Logan Airport), MT 4 mi (6 km)
  2. Columbus, MT 39 mi (63 km)
  3. Rapelje, MT 40 mi (64 km)
  4. Yellowtail Dam, MT 41 mi (66 km)
  5. Hardin, MT 42 mi (68 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 45.7717, -108.4811.