U.S. Frost Dates by Weather Station

NOAA station USC00170833 · Maine

Frost Dates for Bridgewater, ME

NOAA weather station Bridgewater (USC00170833), Maine · elevation 420 ft (128 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 7only 1 spring in 10 still has a frost later
  • Typical last frostMay 2550% chance of a frost after it
  • Typical first fall frostSeptember 1850% chance of a frost before it
  • Frost-free season115 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Bridgewater, MESpring: a frost after May 9 in 9 years out of 10, after May 25 in half of the years, after June 7 in 1 year out of 10. Fall: the first frost comes before September 4 in 1 year out of 10, before September 18 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 115 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 25First frost ~Sep 18Frost season at Bridgewater, MESpring: a frost after May 9 in 9 years out of 10, after May 25 in half of the years, after June 7 in 1 year out of 10. Fall: the first frost comes before September 4 in 1 year out of 10, before September 18 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 115 days.JFMAMJJASONDLast frost ~May 25First frost ~Sep 18
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 7September 4
50% (typical)May 25September 18
90% (likely)May 9October 1
Frost-free season (32°F, 50% chance)
115 days
Hard frost (28°F), last in spring, 50% chance after
May 9
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 21 (3 days later). Frost-free season 119 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 Bridgewater: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 7, 20% June 3, 30% May 31, 40% May 28, 50% May 25, 60% May 22, 70% May 18, 80% May 14, 90% May 9.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 7May 25May 9Fall at Bridgewater: chance of a frost before this dateFall, chance of a frost before the date: 10% September 4, 20% September 8, 30% September 12, 40% September 16, 50% September 18, 60% September 21, 70% September 24, 80% September 27, 90% October 1.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 4Sep 18Oct 1
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.

What these dates mean

June 7, with a 10 % chance of a later light frost, is the cautious spring date and lets a gardener set out tender crops with minimal risk. The 50 % hard-frost date in spring is May 9, indicating an even odds of a hard frost at 28 °F.

The 50 % light-frost date is May 25; there is a 50 % chance of a light frost later than this date. In fall, the 50 % light-frost date is September 18, with a 50 % chance of a light frost earlier than this date. The 50 % hard-frost date in fall is October 1.

September 4, with a 10 % chance of an earlier light frost, is the cautious fall date and signals when a gardener can finish harvesting tender crops. A hard frost at 28 °F matters more than a light frost at 32 °F because it can cause far greater damage to plant tissue.

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 September 4" 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 Bridgewater, MENumbered nearest stations: 1 — Presque Isle, ME — 17 mi; 2 — Houlton, ME — 21 mi; 3 — Caribou, ME — 32 mi; 4 — Van Buren, ME — 51 mi; 5 — Fort Kent, ME — 67 mi.ME25 mi · 40 km1. Presque Isle, ME — 17 mi12. Houlton, ME — 21 mi23. Caribou, ME — 32 mi34. Van Buren, ME — 51 mi45. Fort Kent, ME — 67 mi5
  1. Presque Isle, ME 17 mi (28 km)
  2. Houlton, ME 21 mi (34 km)
  3. Caribou, ME 32 mi (51 km)
  4. Van Buren, ME 51 mi (82 km)
  5. Fort Kent, ME 67 mi (107 km)

Sources

* Hardiness zone 4a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 46.4283, -67.8442.