U.S. Frost Dates by Weather Station

NOAA station USC00246190 · Montana

Frost Dates for Nye #2, MT

NOAA weather station Nye #2 (USC00246190), Montana · elevation 4840 ft (1475 m) · hardiness zone 5a*

  • Lower-risk planting dateafter June 21only 1 spring in 10 still has a frost later
  • Typical last frostJune 150% chance of a frost after it
  • Typical first fall frostSeptember 1150% chance of a frost before it
  • Frost-free season100 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Nye #2, MTSpring: a frost after May 15 in 9 years out of 10, after June 1 in half of the years, after June 21 in 1 year out of 10. Fall: the first frost comes before August 25 in 1 year out of 10, before September 11 in half of the years, before September 26 in 9 years out of 10. Typical frost-free season: 100 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 1First frost ~Sep 11Frost season at Nye #2, MTSpring: a frost after May 15 in 9 years out of 10, after June 1 in half of the years, after June 21 in 1 year out of 10. Fall: the first frost comes before August 25 in 1 year out of 10, before September 11 in half of the years, before September 26 in 9 years out of 10. Typical frost-free season: 100 days.JFMAMJJASONDLast frost ~Jun 1First frost ~Sep 11
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 21August 25
50% (typical)June 1September 11
90% (likely)May 15September 26
Frost-free season (32°F, 50% chance)
100 days
Hard frost (28°F), last in spring, 50% chance after
May 15
Hard frost (28°F), first in fall, 50% chance before
September 25

The last 15 years (2006–2020 normals)

Typical last frost May 28 (4 days earlier than the 30-year normal), typical first fall frost September 11. Frost-free season 106 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 Nye #2: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 21, 20% June 14, 30% June 9, 40% June 5, 50% June 1, 60% May 29, 70% May 25, 80% May 21, 90% May 15.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1Jun 21Jun 1May 15Fall at Nye #2: chance of a frost before this dateFall, chance of a frost before the date: 10% August 25, 20% September 1, 30% September 4, 40% September 7, 50% September 11, 60% September 14, 70% September 18, 80% September 21, 90% September 26.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 25Sep 11Sep 26
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.

What these dates mean

August 25 is the cautious fall date in Nye #2 for finishing the harvest, when there is only a 10 % chance that a light frost has arrived earlier. In spring the cautious date for setting out tender crops is June 21, which carries a 10 % chance of a light frost later. The 50% date is June 1, a 50 % chance of a frost later than this date, and the 50% date is September 11, a 50 % chance of a frost earlier than this date.

Hard-frost thresholds are recorded at 28 °F; the spring hard-frost median is May 15 and the fall hard-frost median is September 25. A hard frost matters more than a light frost because the lower temperature can injure or kill plants that would otherwise survive a 32 °F 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 21" 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 25" 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 Nye #2, MTNumbered nearest stations: 1 — Mystic Lake, MT — 14 mi; 2 — Big Timber, MT — 28 mi; 3 — Columbus, MT — 30 mi; 4 — Rapelje, MT — 46 mi; 5 — Melville, MT — 48 mi.MTWY25 mi · 40 km1. Mystic Lake, MT — 14 mi12. Big Timber, MT — 28 mi23. Columbus, MT — 30 mi34. Rapelje, MT — 46 mi45. Melville, MT — 48 mi5
  1. Mystic Lake, MT 14 mi (22 km)
  2. Big Timber, MT 28 mi (46 km)
  3. Columbus, MT 30 mi (48 km)
  4. Rapelje, MT 46 mi (74 km)
  5. Melville, MT 48 mi (77 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 45.435, -109.8081.