U.S. Frost Dates by Weather Station

NOAA station USC00246601 · Montana

Frost Dates for Plevna, MT

NOAA weather station Plevna (USC00246601), Montana · elevation 2780 ft (847 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 2150% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season121 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Plevna, MTSpring: a frost after May 9 in 9 years out of 10, after May 21 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 20 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 121 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 21First frost ~Sep 20Frost season at Plevna, MTSpring: a frost after May 9 in 9 years out of 10, after May 21 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 20 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 121 days.JFMAMJJASONDLast frost ~May 21First frost ~Sep 20
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)June 4September 5
50% (typical)May 21September 20
90% (likely)May 9October 5
Frost-free season (32°F, 50% chance)
121 days
Hard frost (28°F), last in spring, 50% chance after
May 11
Hard frost (28°F), first in fall, 50% chance before
September 30

The last 15 years (2006–2020 normals)

Typical last frost May 17 (4 days earlier than the 30-year normal), typical first fall frost September 22 (2 days later). Frost-free season 127 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 Plevna: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 30, 30% May 27, 40% May 24, 50% May 21, 60% May 18, 70% May 15, 80% May 13, 90% May 9. Observed last spring frost in recent years: 2021 May 30, 2022 June 1, 2023 May 19, 2024 June 19, 2025 May 21, 2026 May 23.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 21May 92021: May 302022: June 12023: May 192024: June 192025: May 212026: May 23Fall at Plevna: chance of a frost before this dateFall, chance of a frost before the date: 10% September 5, 20% September 10, 30% September 14, 40% September 17, 50% September 20, 60% September 23, 70% September 27, 80% September 30, 90% October 5. Observed first fall frost in recent years: 2021 September 17, 2022 September 10, 2023 October 6, 2024 September 22, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 5Sep 20Oct 52021: September 172022: September 102023: October 62024: September 222025: September 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 30September 17
2022June 1September 10
2023May 19October 6
2024June 19September 22
2025May 21September 6
2026May 23season not over yet

What these dates mean

September 5 is the cautious fall date for finishing the harvest of tender crops in Plevna; there is only a 10 % chance that a light frost has arrived earlier. For the spring season the cautious date is June 4, when the chance of a frost later than that date drops to 10 %. The 50% dates give a midpoint of risk: the 50% date is May 21, meaning a 50 % chance of a frost later than this date, and the 50% date is September 20, meaning a 50 % chance of a frost earlier than this date. The hard-frost median dates are May 11 and September 30. A hard frost at 28 °F can damage plants that survive a light frost at 32 °F, so it is a more critical threshold.

How to read the probabilities

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

  • Spring: "10% after June 4" 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 5" 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 Plevna, MTNumbered nearest stations: 1 — Carlyle, MT — 25 mi; 2 — Mildred, MT — 32 mi; 3 — Ekalaka, MT — 37 mi; 4 — Mizpah, MT — 38 mi; 5 — Terry, MT — 45 mi.NDSD25 mi · 40 km1. Carlyle, MT — 25 mi12. Mildred, MT — 32 mi23. Ekalaka, MT — 37 mi34. Mizpah, MT — 38 mi45. Terry, MT — 45 mi5
  1. Carlyle, MT 25 mi (40 km)
  2. Mildred, MT 32 mi (51 km)
  3. Ekalaka, MT 37 mi (59 km)
  4. Mizpah, MT 38 mi (61 km)
  5. Terry, MT 45 mi (73 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: 46.4178, -104.5164.