U.S. Frost Dates by Weather Station

NOAA station USC00243530 · Montana

Frost Dates for Gildford, MT

NOAA weather station Gildford (USC00243530), Montana · elevation 2820 ft (860 m) · hardiness zone 3b*

  • Lower-risk planting dateafter June 7only 1 spring in 10 still has a frost later
  • Typical last frostMay 2450% chance of a frost after it
  • Typical first fall frostSeptember 1550% chance of a frost before it
  • Frost-free season114 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Gildford, MTSpring: a frost after May 12 in 9 years out of 10, after May 24 in half of the years, after June 7 in 1 year out of 10. Fall: the first frost comes before August 29 in 1 year out of 10, before September 15 in half of the years, before September 28 in 9 years out of 10. Typical frost-free season: 114 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 24First frost ~Sep 15Frost season at Gildford, MTSpring: a frost after May 12 in 9 years out of 10, after May 24 in half of the years, after June 7 in 1 year out of 10. Fall: the first frost comes before August 29 in 1 year out of 10, before September 15 in half of the years, before September 28 in 9 years out of 10. Typical frost-free season: 114 days.JFMAMJJASONDLast frost ~May 24First frost ~Sep 15
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 7August 29
50% (typical)May 24September 15
90% (likely)May 12September 28
Frost-free season (32°F, 50% chance)
114 days
Hard frost (28°F), last in spring, 50% chance after
May 12
Hard frost (28°F), first in fall, 50% chance before
September 26

The last 15 years (2006–2020 normals)

Typical last frost May 23 (1 day earlier than the 30-year normal), typical first fall frost September 18 (3 days later). Frost-free season 118 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 Gildford: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 7, 20% June 2, 30% May 31, 40% May 27, 50% May 24, 60% May 21, 70% May 19, 80% May 16, 90% May 12. Observed last spring frost in recent years: 2021 May 22, 2022 May 31, 2023 April 28, 2025 May 22, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 7May 24May 122021: May 222022: May 312023: April 282025: May 222026: May 22Fall at Gildford: chance of a frost before this dateFall, chance of a frost before the date: 10% August 29, 20% September 4, 30% September 8, 40% September 12, 50% September 15, 60% September 18, 70% September 21, 80% September 24, 90% September 28. Observed first fall frost in recent years: 2021 September 16, 2022 September 10, 2023 October 6, 2024 October 1, 2025 October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 29Sep 15Sep 282021: September 162022: September 102023: October 62024: October 12025: October 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 22September 16
2022May 31September 10
2023April 28October 6
2024incomplete recordOctober 1
2025May 22October 5
2026May 22season not over yet

What these dates mean

The 32 °F 50 % dates in Gildford are May 24 and September 15, a span of 114 days that frames the period when tender crops can be grown with balanced frost risk. For a gardener these median dates simply mark the point at which a light frost is as likely as not; they are not themselves frost dates.

In spring the cautious date for setting out tender crops is June 7, when there is only a 10 % chance of a light frost occurring later. Planting on May 12 carries a 90 % chance and is a gamble. In fall the cautious date to finish harvesting tender crops is August 29, with a 10 % chance of a light frost having arrived earlier, while September 28 involves a 90 % chance and is risky.

The 28 °F hard-frost 50 % dates are May 12 and September 26; a hard frost can damage plants that survive a 32 °F light frost, making it a more critical threshold for growers in this location.

How to read the probabilities

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

  • Spring: "10% after June 7" 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 29" 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 Gildford, MTNumbered nearest stations: 1 — Fort Assiniboine, MT — 23 mi; 2 — Havre, MT — 25 mi; 3 — Simpson 6 N - Wildhorse, MT — 30 mi; 4 — Loma, MT — 44 mi; 5 — Chinook, MT — 49 mi.MT25 mi · 40 km1. Fort Assiniboine, MT — 23 mi12. Havre, MT — 25 mi23. Simpson 6 N - Wildhorse, MT — 30 mi34. Loma, MT — 44 mi45. Chinook, MT — 49 mi5
  1. Fort Assiniboine, MT 23 mi (38 km)
  2. Havre, MT 25 mi (40 km)
  3. Simpson 6 N - Wildhorse, MT 30 mi (49 km)
  4. Loma, MT 44 mi (71 km)
  5. Chinook, MT 49 mi (79 km)

Sources

* Hardiness zone 3b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.5647, -110.3028.