U.S. Frost Dates by Weather Station

NOAA station USC00247864 · Montana

Frost Dates for Stanford, MT

NOAA weather station Stanford (USC00247864), Montana · elevation 4860 ft (1481 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 15only 1 spring in 10 still has a frost later
  • Typical last frostMay 2550% chance of a frost after it
  • Typical first fall frostSeptember 2150% chance of a frost before it
  • Frost-free season118 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Stanford, MTSpring: a frost after May 10 in 9 years out of 10, after May 25 in half of the years, after June 15 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 21 in half of the years, before October 3 in 9 years out of 10. Typical frost-free season: 118 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 25First frost ~Sep 21Frost season at Stanford, MTSpring: a frost after May 10 in 9 years out of 10, after May 25 in half of the years, after June 15 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 21 in half of the years, before October 3 in 9 years out of 10. Typical frost-free season: 118 days.JFMAMJJASONDLast frost ~May 25First frost ~Sep 21
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.Today

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 15September 6
50% (typical)May 25September 21
90% (likely)May 10October 3
Frost-free season (32°F, 50% chance)
118 days
Hard frost (28°F), last in spring, 50% chance after
May 10
Hard frost (28°F), first in fall, 50% chance before
October 1

The last 15 years (2006–2020 normals)

Typical last frost May 24 (1 day earlier than the 30-year normal), typical first fall frost September 22 (1 day later). Frost-free season 120 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 Stanford: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 15, 20% June 6, 30% May 31, 40% May 28, 50% May 25, 60% May 22, 70% May 19, 80% May 15, 90% May 10. Observed last spring frost in recent years: 2021 May 29, 2022 May 22, 2023 April 28, 2024 May 21, 2025 June 23, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 15May 25May 102021: May 292022: May 222023: April 282024: May 212025: June 232026: May 19Fall at Stanford: chance of a frost before this dateFall, chance of a frost before the date: 10% September 6, 20% September 11, 30% September 15, 40% September 18, 50% September 21, 60% September 24, 70% September 26, 80% September 29, 90% October 3. Observed first fall frost in recent years: 2021 September 30, 2022 October 13, 2023 October 2, 2024 October 1, 2025 October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 6Sep 21Oct 32021: September 302022: October 132023: October 22024: 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 29September 30
2022May 22October 13
2023April 28October 2
2024May 21October 1
2025June 23October 5
2026May 19season not over yet

What these dates mean

The 118 days between the 50% dates in Stanford, May 25 and September 21, mark the primary period when light frost is equally likely or unlikely. For a gardener this means that up to May 25 the odds of a light frost are higher, and they become greater again later in the season, relative to the September 21 median, framing planting and harvesting choices around a balanced risk point.

In spring the cautious date for setting out tender crops is June 15, when there is only a 10 % chance of a later light frost; planting before the 90 % chance date of May 10 would be a gamble. In fall the cautious date to finish harvesting tender crops is September 6, with a 10 % chance that frost has already arrived, while counting on crops until October 3 carries a 90 % chance of an early frost. A hard frost at 28 °F, reflected by the median dates May 10 and October 1, can injure plants that survive a 32 °F light frost, making it a more severe threat.

How to read the probabilities

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

  • Spring: "10% after June 15" 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 Stanford, MTNumbered nearest stations: 1 — Lewistown, MT — 37 mi; 2 — Millegan, MT — 48 mi; 3 — Loma, MT — 56 mi; 4 — Great Falls, MT — 59 mi; 5 — Ryegate, MT — 60 mi.25 mi · 40 km1. Lewistown, MT — 37 mi12. Millegan, MT — 48 mi23. Loma, MT — 56 mi34. Great Falls, MT — 59 mi45. Ryegate, MT — 60 mi5
  1. Lewistown, MT 37 mi (59 km)
  2. Millegan, MT 48 mi (78 km)
  3. Loma, MT 56 mi (89 km)
  4. Great Falls, MT 59 mi (94 km)
  5. Ryegate, MT 60 mi (96 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: 47.155, -110.2239.