U.S. Frost Dates by Weather Station

NOAA station USC00244558 · Montana

Frost Dates near Kalispell, MT

NOAA weather station Kalispell Glacier Airport (USC00244558), Montana · elevation 2957 ft (901 m) · hardiness zone 5b*

Kalispell is the nearest town to the station (7.8 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter June 22only 1 spring in 10 still has a frost later
  • Typical last frostMay 3150% chance of a frost after it
  • Typical first fall frostSeptember 1050% chance of a frost before it
  • Frost-free season100 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season near Kalispell, MTSpring: a frost after May 13 in 9 years out of 10, after May 31 in half of the years, after June 22 in 1 year out of 10. Fall: the first frost comes before August 26 in 1 year out of 10, before September 10 in half of the years, before September 25 in 9 years out of 10. Typical frost-free season: 100 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 31First frost ~Sep 10Frost season near Kalispell, MTSpring: a frost after May 13 in 9 years out of 10, after May 31 in half of the years, after June 22 in 1 year out of 10. Fall: the first frost comes before August 26 in 1 year out of 10, before September 10 in half of the years, before September 25 in 9 years out of 10. Typical frost-free season: 100 days.JFMAMJJASONDLast frost ~May 31First frost ~Sep 10
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 22August 26
50% (typical)May 31September 10
90% (likely)May 13September 25
Frost-free season (32°F, 50% chance)
100 days
Hard frost (28°F), last in spring, 50% chance after
May 10
Hard frost (28°F), first in fall, 50% chance before
September 27

The last 15 years (2006–2020 normals)

Typical last frost May 23 (8 days earlier than the 30-year normal), typical first fall frost September 11 (1 day later). Frost-free season 111 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 near Kalispell: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 22, 20% June 14, 30% June 7, 40% June 3, 50% May 31, 60% May 27, 70% May 23, 80% May 19, 90% May 13. Observed last spring frost in recent years: 2021 May 29, 2022 May 23, 2023 June 22, 2024 May 31, 2025 May 6, 2026 May 21.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1Jun 22May 31May 132021: May 292022: May 232023: June 222024: May 312025: May 62026: May 21Fall near Kalispell: chance of a frost before this dateFall, chance of a frost before the date: 10% August 26, 20% August 31, 30% September 4, 40% September 7, 50% September 10, 60% September 13, 70% September 17, 80% September 21, 90% September 25. Observed first fall frost in recent years: 2021 September 16, 2022 September 10, 2023 October 5, 2024 September 22, 2025 September 27.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 26Sep 10Sep 252021: September 162022: September 102023: October 52024: September 222025: September 27
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 29September 16
2022May 23September 10
2023June 22October 5
2024May 31September 22
2025May 6September 27
2026May 21season not over yet

What these dates mean

August 26 is the cautious fall date for the Kalispell area, marking the point when there is only a 10 % chance that a light frost has already arrived and providing a reliable target for finishing the harvest of tender crops. In spring, the cautious date for setting out tender crops is June 22, while planting on May 13 carries a 90 % chance of a frost and is therefore a gamble. The 50 % date of May 31 indicates an even-odds point, meaning a 50 % chance of a light frost later than this date. The fall 50 % date of September 10 indicates a 50 % chance of a light frost earlier than this date. Hard-frost thresholds (28 °F) reach the 50 % dates of May 10 in spring and September 27 in fall, and a hard frost can damage plant tissue that survives a light frost, so it matters more to gardeners.

How to read the probabilities

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

  • Spring: "10% after June 22" 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 26" 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 Kalispell, MTNumbered nearest stations: 1 — Creston, MT — 10 mi; 2 — West Glacier, MT — 19 mi; 3 — Libby Dam (Base), MT — 49 mi; 4 — Lindbergh Lake, MT — 67 mi; 5 — near Thompson Falls, MT — 71 mi.MTID25 mi · 40 km1. Creston, MT — 10 mi12. West Glacier, MT — 19 mi23. Libby Dam (Base), MT — 49 mi34. Lindbergh Lake, MT — 67 mi45. near Thompson Falls, MT — 71 mi5
  1. Creston, MT 10 mi (16 km)
  2. West Glacier, MT 19 mi (30 km)
  3. Libby Dam (Base), MT 49 mi (79 km)
  4. Lindbergh Lake, MT 67 mi (108 km)
  5. near Thompson Falls, MT 71 mi (114 km)

Sources

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

Station coordinates: 48.3042, -114.2636.