U.S. Frost Dates by Weather Station

NOAA station USC00241974 · Montana

Frost Dates for Conrad, MT

NOAA weather station Conrad (USC00241974), Montana · elevation 3550 ft (1082 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 3only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostSeptember 1950% chance of a frost before it
  • Frost-free season119 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Conrad, MTSpring: a frost after May 9 in 9 years out of 10, after May 20 in half of the years, after June 3 in 1 year out of 10. Fall: the first frost comes before September 4 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: 119 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Sep 19Frost season at Conrad, MTSpring: a frost after May 9 in 9 years out of 10, after May 20 in half of the years, after June 3 in 1 year out of 10. Fall: the first frost comes before September 4 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: 119 days.JFMAMJJASONDLast frost ~May 20First 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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 3September 4
50% (typical)May 20September 19
90% (likely)May 9October 2
Frost-free season (32°F, 50% chance)
119 days
Hard frost (28°F), last in spring, 50% chance after
May 8
Hard frost (28°F), first in fall, 50% chance before
September 30

The last 15 years (2006–2020 normals)

Typical last frost May 19 (1 day earlier than the 30-year normal), typical first fall frost September 20 (1 day later). Frost-free season 125 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 Conrad: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 3, 20% May 30, 30% May 26, 40% May 23, 50% May 20, 60% May 18, 70% May 15, 80% May 13, 90% May 9. Observed last spring frost in recent years: 2021 May 22, 2022 May 22, 2023 April 28, 2024 May 21, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 3May 20May 92021: May 222022: May 222023: April 282024: May 212026: May 22Fall at Conrad: chance of a frost before this dateFall, chance of a frost before the date: 10% September 4, 20% September 10, 30% September 14, 40% September 17, 50% September 19, 60% September 22, 70% September 24, 80% September 27, 90% October 2. Observed first fall frost in recent years: 2021 September 17, 2022 September 21, 2023 September 29, 2024 September 30, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 4Sep 19Oct 22021: September 172022: September 212023: September 292024: 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 22September 17
2022May 22September 21
2023April 28September 29
2024May 21September 30
2025incomplete recordOctober 6
2026May 22season not over yet

What these dates mean

June 3 is the cautious spring date in Conrad, carrying only a 10% chance that a light frost will occur later; it gives gardeners a reliable point to set out tender crops. The station’s 25-year record, situated at 3550 ft in USDA zone 4a, underpins these probabilities.

The 50% date is May 20, a 50% chance of a light frost later than this date, while the fall 50% date is September 19, a 50% chance of a light frost earlier than this date. The cautious fall date is September 4, with only a 10% chance that a light frost has already arrived, allowing the final harvest of tender crops to be scheduled with confidence.

Hard-frost dates—May 8 in spring and September 30 in fall—matter more than light-frost dates because a temperature of 28 °F can damage plants that survive 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 3" 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 4" 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 Conrad, MTNumbered nearest stations: 1 — Choteau, MT — 27 mi; 2 — Cut Bank, MT — 36 mi; 3 — Fairfield, MT — 39 mi; 4 — Sun River, MT — 49 mi; 5 — Great Falls, MT — 55 mi.MT25 mi · 40 km1. Choteau, MT — 27 mi12. Cut Bank, MT — 36 mi23. Fairfield, MT — 39 mi34. Sun River, MT — 49 mi45. Great Falls, MT — 55 mi5
  1. Choteau, MT 27 mi (43 km)
  2. Cut Bank, MT 36 mi (57 km)
  3. Fairfield, MT 39 mi (62 km)
  4. Sun River, MT 49 mi (79 km)
  5. Great Falls, MT 55 mi (89 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: 48.1736, -111.9503.