U.S. Frost Dates by Weather Station

NOAA station USC00246691 · Montana

Frost Dates for Powderville, MT

NOAA weather station Powderville 8 NNE (USC00246691), Montana · elevation 2800 ft (853 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 31only 1 spring in 10 still has a frost later
  • Typical last frostMay 1350% chance of a frost after it
  • Typical first fall frostSeptember 2550% chance of a frost before it
  • Frost-free season132 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Powderville, MTSpring: a frost after May 1 in 9 years out of 10, after May 13 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 25 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 132 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 13First frost ~Sep 25Frost season at Powderville, MTSpring: a frost after May 1 in 9 years out of 10, after May 13 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 25 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 132 days.JFMAMJJASONDLast frost ~May 13First frost ~Sep 25
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)May 31September 6
50% (typical)May 13September 25
90% (likely)May 1October 9
Frost-free season (32°F, 50% chance)
132 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 10 (3 days earlier than the 30-year normal), typical first fall frost September 27 (2 days later). Frost-free season 137 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 Powderville: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 31, 20% May 24, 30% May 20, 40% May 16, 50% May 13, 60% May 11, 70% May 8, 80% May 5, 90% May 1. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 April 30, 2024 May 4, 2025 May 2, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 31May 13May 12021: May 112022: May 222023: April 302024: May 42025: May 22026: May 7Fall at Powderville: chance of a frost before this dateFall, chance of a frost before the date: 10% September 6, 20% September 15, 30% September 19, 40% September 22, 50% September 25, 60% September 28, 70% October 1, 80% October 4, 90% October 9. Observed first fall frost in recent years: 2021 September 17, 2022 October 7, 2023 October 6, 2024 September 22, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 6Sep 25Oct 92021: September 172022: October 72023: 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 11September 17
2022May 22October 7
2023April 30October 6
2024May 4September 22
2025May 2September 6
2026May 7season not over yet

What these dates mean

The 132 days between the 50% light-frost dates of May 13 and September 25 frame the median frost-free window for Powderville gardeners. These dates mark the point at which a light frost is equally likely to occur later in spring or earlier in fall.

In spring the cautious date for setting out tender crops is May 31, when there is only a 10 % chance of a later frost; planting on May 1 carries a 90 % chance of a later frost and is therefore a gamble. In fall the cautious date to finish harvesting tender crops is September 6, which carries only a 10 % chance that a frost has already arrived; aiming for October 9 entails a 90 % chance that a frost has arrived and is a gamble.

A hard frost at 28 °F can damage plants that would otherwise survive a light frost 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 31" 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 6" 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 Powderville, MTNumbered nearest stations: 1 — Ekalaka, MT — 24 mi; 2 — Mizpah, MT — 32 mi; 3 — Ridgeway, MT — 37 mi; 4 — Plevna, MT — 46 mi; 5 — Camp Crook, SD — 55 mi.NDSD25 mi · 40 km1. Ekalaka, MT — 24 mi12. Mizpah, MT — 32 mi23. Ridgeway, MT — 37 mi34. Plevna, MT — 46 mi45. Camp Crook, SD — 55 mi5
  1. Ekalaka, MT 24 mi (38 km)
  2. Mizpah, MT 32 mi (52 km)
  3. Ridgeway, MT 37 mi (60 km)
  4. Plevna, MT 46 mi (74 km)
  5. Camp Crook, SD 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: 45.8525, -105.035.