U.S. Frost Dates by Weather Station

NOAA station USW00014607 · Maine

Frost Dates for Caribou, ME

NOAA weather station Caribou Municipal Airport (USW00014607), Maine · elevation 624 ft (190 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Caribou, MESpring: a frost after April 27 in 9 years out of 10, after May 7 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before October 1 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 1Frost season at Caribou, MESpring: a frost after April 27 in 9 years out of 10, after May 7 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before October 1 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 143 days.JFMAMJJASONDLast frost ~May 7First frost ~Oct 1
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)May 24September 17
50% (typical)May 7October 1
90% (likely)April 27October 14
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 7 (same as the 30-year normal), typical first fall frost October 1. Frost-free season 145 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 Caribou: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 17, 30% May 13, 40% May 10, 50% May 7, 60% May 5, 70% May 2, 80% April 30, 90% April 27. Observed last spring frost in recent years: 2021 May 28, 2022 May 9, 2023 May 23, 2024 May 10, 2025 May 1, 2026 May 30.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 24May 7Apr 272021: May 282022: May 92023: May 232024: May 102025: May 12026: May 30Fall at Caribou: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 22, 30% September 25, 40% September 28, 50% October 1, 60% October 2, 70% October 5, 80% October 7, 90% October 14. Observed first fall frost in recent years: 2021 October 25, 2022 September 30, 2023 October 23, 2024 October 9, 2025 September 21.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 17Oct 1Oct 142021: October 252022: September 302023: October 232024: October 92025: September 21
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 28October 25
2022May 9September 30
2023May 23October 23
2024May 10October 9
2025May 1September 21
2026May 30season not over yet

What these dates mean

The cautious fall date in Caribou for finishing the harvest is September 17, when there is only a 10% chance that a light frost has arrived. The cautious spring date for setting out tender crops is May 24, with a 10% chance of a later frost, while an early planting on April 27 carries a 90% gamble.

The light-frost 50% date in spring is May 7, a 50% chance of a frost later than this date; the light-frost 50% date in fall is October 1, a 50% chance of a frost earlier than this date. The hard-frost 50% dates are April 26 and October 12.

A hard frost at 28 °F can damage plants that survive a 32 °F light frost, making it a more serious threat.

How to read the probabilities

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

  • Spring: "10% after May 24" 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 17" 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 Caribou, MENumbered nearest stations: 1 — Presque Isle, ME — 15 mi; 2 — Van Buren, ME — 21 mi; 3 — Bridgewater, ME — 32 mi; 4 — Fort Kent, ME — 38 mi; 5 — Houlton, ME — 53 mi.ME25 mi · 40 km1. Presque Isle, ME — 15 mi12. Van Buren, ME — 21 mi23. Bridgewater, ME — 32 mi34. Fort Kent, ME — 38 mi45. Houlton, ME — 53 mi5
  1. Presque Isle, ME 15 mi (24 km)
  2. Van Buren, ME 21 mi (33 km)
  3. Bridgewater, ME 32 mi (51 km)
  4. Fort Kent, ME 38 mi (61 km)
  5. Houlton, ME 53 mi (85 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: 46.8706, -68.0172.