U.S. Frost Dates by Weather Station

NOAA station USC00246238 · Montana

Frost Dates for Opheim, MT

NOAA weather station Opheim 12 SSE (USC00246238), Montana · elevation 2936 ft (895 m) · hardiness zone 3b*

  • Lower-risk planting dateafter June 23only 1 spring in 10 still has a frost later
  • Typical last frostJune 550% chance of a frost after it
  • Typical first fall frostSeptember 250% chance of a frost before it
  • Frost-free season89 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Opheim, MTSpring: a frost after May 22 in 9 years out of 10, after June 5 in half of the years, after June 23 in 1 year out of 10. Fall: the first frost comes before August 15 in 1 year out of 10, before September 2 in half of the years, before September 17 in 9 years out of 10. Typical frost-free season: 89 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 5First frost ~Sep 2Frost season at Opheim, MTSpring: a frost after May 22 in 9 years out of 10, after June 5 in half of the years, after June 23 in 1 year out of 10. Fall: the first frost comes before August 15 in 1 year out of 10, before September 2 in half of the years, before September 17 in 9 years out of 10. Typical frost-free season: 89 days.JFMAMJJASONDLast frost ~Jun 5First frost ~Sep 2
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.Today

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 23August 15
50% (typical)June 5September 2
90% (likely)May 22September 17
Frost-free season (32°F, 50% chance)
89 days
Hard frost (28°F), last in spring, 50% chance after
May 24
Hard frost (28°F), first in fall, 50% chance before
September 14

The last 15 years (2006–2020 normals)

Typical last frost June 3 (2 days earlier than the 30-year normal), typical first fall frost September 2. Frost-free season 88 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 Opheim: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 23, 20% June 16, 30% June 11, 40% June 8, 50% June 5, 60% June 2, 70% May 31, 80% May 27, 90% May 22. Observed last spring frost in recent years: 2021 June 21, 2022 June 3, 2023 June 10, 2024 May 4.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1Jun 23Jun 5May 222021: June 212022: June 32023: June 102024: May 4Fall at Opheim: chance of a frost before this dateFall, chance of a frost before the date: 10% August 15, 20% August 23, 30% August 28, 40% August 31, 50% September 2, 60% September 5, 70% September 8, 80% September 12, 90% September 17. Observed first fall frost in recent years: 2021 September 14, 2022 September 9, 2023 September 15, 2024 September 5.Fall: first frostChance of a frost before this date10%50%90%Aug 1Sep 1Oct 1Aug 15Sep 2Sep 172021: September 142022: September 92023: September 152024: September 5
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
2021June 21September 14
2022June 3September 9
2023June 10September 15
2024May 4September 5
2025no datano data
2026no dataseason not over yet

What these dates mean

The cautious fall date for finishing the harvest in Opheim is August 15, when there is only a 10 % chance that a light frost has already arrived.

For tender crops, a cautious plan uses June 23 in spring and August 15 in fall; June 23 carries only a 10 % chance of a light frost later, while August 15 carries only a 10 % chance of a light frost earlier. The 50% dates for light frost are June 5 in spring and September 2 in fall. The median hard-frost dates are May 24 in spring and September 14 in fall. These dates are derived from 29 years of NOAA normals and the interval between the two 32°F 50% dates is 89 days.

In Opheim, a hard frost at 28 °F can damage plant tissue more severely than a light frost at 32 °F, so its timing is critical for tender crops.

How to read the probabilities

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

  • Spring: "10% after June 23" 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 August 15" 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 Opheim, MTNumbered nearest stations: 1 — Glasgow, MT — 36 mi; 2 — Glasgow #2, MT — 38 mi; 3 — Scobey, MT — 39 mi; 4 — Fort Peck Power Plant, MT — 47 mi; 5 — Bredette, MT — 48 mi.MT25 mi · 40 km1. Glasgow, MT — 36 mi12. Glasgow #2, MT — 38 mi23. Scobey, MT — 39 mi34. Fort Peck Power Plant, MT — 47 mi45. Bredette, MT — 48 mi5
  1. Glasgow, MT 36 mi (58 km)
  2. Glasgow #2, MT 38 mi (61 km)
  3. Scobey, MT 39 mi (64 km)
  4. Fort Peck Power Plant, MT 47 mi (76 km)
  5. Bredette, MT 48 mi (77 km)

Sources

* Hardiness zone 3b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.6956, -106.3153.