U.S. Frost Dates by Weather Station

NOAA station USC00170814 · Maine

Frost Dates for Brassua Dam, ME

NOAA weather station Brassua Dam (USC00170814), Maine · elevation 1069 ft (326 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 2350% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season128 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Brassua Dam, MESpring: a frost after May 7 in 9 years out of 10, after May 23 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 29 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 128 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 23First frost ~Sep 29Frost season at Brassua Dam, MESpring: a frost after May 7 in 9 years out of 10, after May 23 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 29 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 128 days.JFMAMJJASONDLast frost ~May 23First frost ~Sep 29
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 4September 16
50% (typical)May 23September 29
90% (likely)May 7October 11
Frost-free season (32°F, 50% chance)
128 days
Hard frost (28°F), last in spring, 50% chance after
May 9
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 20 (3 days earlier than the 30-year normal), typical first fall frost September 29. Frost-free season 129 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 Brassua Dam: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% June 1, 30% May 28, 40% May 25, 50% May 23, 60% May 20, 70% May 17, 80% May 14, 90% May 7. Observed last spring frost in recent years: 2021 May 30, 2022 May 10, 2023 May 23, 2024 May 11, 2025 May 12.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 23May 72021: May 302022: May 102023: May 232024: May 112025: May 12Fall at Brassua Dam: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 22, 30% September 24, 40% September 27, 50% September 29, 60% October 1, 70% October 4, 80% October 6, 90% October 11. Observed first fall frost in recent years: 2021 October 4, 2022 September 30, 2023 October 14, 2024 October 12, 2025 September 20.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 29Oct 112021: October 42022: September 302023: October 142024: October 122025: September 20
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 30October 4
2022May 10September 30
2023May 23October 14
2024May 11October 12
2025May 12September 20
2026incomplete recordseason not over yet

What these dates mean

June 4 is the cautious spring date, letting a gardener set out tender crops when the chance of a light frost later is only 10 percent.

The 50 percent dates – May 23 for spring and September 29 for fall – are the median points where a light frost is equally likely to occur after (spring) or before (fall) the date; they are not frost dates themselves. For a low-risk plan in autumn, September 16 serves as the cautious date, with just a 10 percent chance that a light frost has arrived earlier. The hard-frost 50 percent dates are May 9 in spring and October 10 in fall.

A hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F, 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 June 4" 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 16" 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 Brassua Dam, MENumbered nearest stations: 1 — Jackman, ME — 21 mi; 2 — Eustis, ME — 45 mi; 3 — Dover-Foxcroft, ME — 45 mi; 4 — Corinna, ME — 58 mi; 5 — Madison, ME — 60 mi.MENH25 mi · 40 km1. Jackman, ME — 21 mi12. Eustis, ME — 45 mi23. Dover-Foxcroft, ME — 45 mi34. Corinna, ME — 58 mi45. Madison, ME — 60 mi5
  1. Jackman, ME 21 mi (34 km)
  2. Eustis, ME 45 mi (72 km)
  3. Dover-Foxcroft, ME 45 mi (72 km)
  4. Corinna, ME 58 mi (94 km)
  5. Madison, ME 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: 45.6603, -69.812.