U.S. Frost Dates by Weather Station

NOAA station USC00242689 · Montana

Frost Dates for Ekalaka, MT

NOAA weather station Ekalaka (USC00242689), Montana · elevation 3432 ft (1046 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostSeptember 2350% chance of a frost before it
  • Frost-free season126 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Ekalaka, MTSpring: a frost after May 7 in 9 years out of 10, after May 20 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 7 in 1 year out of 10, before September 23 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 126 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Sep 23Frost season at Ekalaka, MTSpring: a frost after May 7 in 9 years out of 10, after May 20 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 7 in 1 year out of 10, before September 23 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 126 days.JFMAMJJASONDLast frost ~May 20First frost ~Sep 23
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 1September 7
50% (typical)May 20September 23
90% (likely)May 7October 7
Frost-free season (32°F, 50% chance)
126 days
Hard frost (28°F), last in spring, 50% chance after
May 10
Hard frost (28°F), first in fall, 50% chance before
October 2

The last 15 years (2006–2020 normals)

Typical last frost May 17 (3 days earlier than the 30-year normal), typical first fall frost September 24 (1 day later). Frost-free season 128 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 Ekalaka: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 28, 30% May 25, 40% May 23, 50% May 20, 60% May 17, 70% May 14, 80% May 11, 90% May 7. Observed last spring frost in recent years: 2021 May 13, 2022 May 22, 2023 May 19, 2024 June 19, 2025 June 9.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 20May 72021: May 132022: May 222023: May 192024: June 192025: June 9Fall at Ekalaka: chance of a frost before this dateFall, chance of a frost before the date: 10% September 7, 20% September 12, 30% September 17, 40% September 21, 50% September 23, 60% September 26, 70% September 29, 80% October 2, 90% October 7. Observed first fall frost in recent years: 2021 September 17, 2022 September 25, 2023 October 6, 2024 October 1, 2025 September 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 7Sep 23Oct 72021: September 172022: September 252023: October 62024: October 12025: 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
2021May 13September 17
2022May 22September 25
2023May 19October 6
2024June 19October 1
2025June 9September 5
2026incomplete recordseason not over yet

What these dates mean

September 7 is the cautious fall date in Ekalaka for finishing the harvest of tender crops; only a 10 % chance exists that a light frost has arrived earlier. In spring the cautious date for setting out those crops is June 1, when there is a 10 % chance of a light frost later.

The 50 % dates—May 20 for spring and September 23 for fall—mark the day when a gardener faces an even 50 % chance of a light frost occurring later in spring or earlier in fall. A gamble exists at the early-spring date of May 7, which carries a 90 % chance of a frost later, and at the late-fall date of October 7, which carries a 90 % chance of a frost earlier. The hard-frost median dates are May 10 in spring and October 2 in fall, and a hard frost matters more because temperatures of 28 °F can damage plant tissue that survives a light frost.

How to read the probabilities

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

  • Spring: "10% after June 1" 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 7" 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 Ekalaka, MTNumbered nearest stations: 1 — Powderville, MT — 24 mi; 2 — Ridgeway, MT — 27 mi; 3 — Camp Crook, SD — 36 mi; 4 — Plevna, MT — 37 mi; 5 — Mizpah, MT — 45 mi.NDSD25 mi · 40 km1. Powderville, MT — 24 mi12. Ridgeway, MT — 27 mi23. Camp Crook, SD — 36 mi34. Plevna, MT — 37 mi45. Mizpah, MT — 45 mi5
  1. Powderville, MT 24 mi (38 km)
  2. Ridgeway, MT 27 mi (43 km)
  3. Camp Crook, SD 36 mi (58 km)
  4. Plevna, MT 37 mi (59 km)
  5. Mizpah, MT 45 mi (73 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: 45.8864, -104.5478.