U.S. Frost Dates by Weather Station

NOAA station USW00014764 · Maine

Frost Dates for Portland, ME

NOAA weather station Portland International Jetport (USW00014764), Maine · elevation 45 ft (14 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 7only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 1550% chance of a frost before it
  • Frost-free season170 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Portland, MESpring: a frost after April 16 in 9 years out of 10, after April 26 in half of the years, after May 7 in 1 year out of 10. Fall: the first frost comes before October 2 in 1 year out of 10, before October 15 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 170 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 15Frost season at Portland, MESpring: a frost after April 16 in 9 years out of 10, after April 26 in half of the years, after May 7 in 1 year out of 10. Fall: the first frost comes before October 2 in 1 year out of 10, before October 15 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 170 days.JFMAMJJASONDLast frost ~Apr 26First frost ~Oct 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)May 7October 2
50% (typical)April 26October 15
90% (likely)April 16October 30
Frost-free season (32°F, 50% chance)
170 days
Hard frost (28°F), last in spring, 50% chance after
April 14
Hard frost (28°F), first in fall, 50% chance before
October 27

The last 15 years (2006–2020 normals)

Typical last frost April 23 (3 days earlier than the 30-year normal), typical first fall frost October 21 (6 days later). Frost-free season 179 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 Portland: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 7, 20% May 3, 30% May 1, 40% April 29, 50% April 26, 60% April 24, 70% April 22, 80% April 20, 90% April 16. Observed last spring frost in recent years: 2021 April 22, 2022 May 9, 2023 May 18, 2024 April 27, 2025 April 21, 2026 April 25.Spring: last frostChance of a frost after this date10%50%90%May 1May 7Apr 26Apr 162021: April 222022: May 92023: May 182024: April 272025: April 212026: April 25Fall at Portland: chance of a frost before this dateFall, chance of a frost before the date: 10% October 2, 20% October 5, 30% October 9, 40% October 11, 50% October 15, 60% October 17, 70% October 21, 80% October 25, 90% October 30. Observed first fall frost in recent years: 2021 October 24, 2022 October 9, 2023 October 31, 2024 October 17, 2025 October 10.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 2Oct 15Oct 302021: October 242022: October 92023: October 312024: October 172025: October 10
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
2021April 22October 24
2022May 9October 9
2023May 18October 31
2024April 27October 17
2025April 21October 10
2026April 25season not over yet

What these dates mean

The 170 days between the 50% dates in Portland define the central window in which the odds of a light frost are roughly even. The median spring light-frost date is April 26 and the median fall light-frost date is October 15; a gardener can regard these as the points where a frost is just as likely to have occurred as not.

For a cautious planting plan the spring cautious date is May 7, which carries only a 10 % chance of a frost later, while the fall cautious date is October 2, with only a 10 % chance of a frost earlier. The 50% hard-frost dates are April 14 in spring and October 27 in fall, marking the moments when a freeze to 28 °F is equally probable.

A hard frost at 28 °F can injure or kill plants that would survive a light frost at 32 °F, so it represents a greater risk for tender crops.

How to read the probabilities

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

  • Spring: "10% after May 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 October 2" 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 Portland, MENumbered nearest stations: 1 — Gray, ME — 17 mi; 2 — Kennebunkport, ME — 22 mi; 3 — Bridgton, ME — 37 mi; 4 — Newcastle, ME — 47 mi; 5 — Gardiner, ME — 47 mi.MENH25 mi · 40 km1. Gray, ME — 17 mi12. Kennebunkport, ME — 22 mi23. Bridgton, ME — 37 mi34. Newcastle, ME — 47 mi45. Gardiner, ME — 47 mi5
  1. Gray, ME 17 mi (27 km)
  2. Kennebunkport, ME 22 mi (35 km)
  3. Bridgton, ME 37 mi (59 km)
  4. Newcastle, ME 47 mi (75 km)
  5. Gardiner, ME 47 mi (76 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 43.6497, -70.3003.