U.S. Frost Dates by Weather Station

NOAA station USC00274399 · New Hampshire

Frost Dates for Keene, NH

NOAA weather station Keene (USC00274399), New Hampshire · elevation 511 ft (156 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 28only 1 spring in 10 still has a frost later
  • Typical last frostMay 1450% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season138 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Keene, NHSpring: a frost after April 30 in 9 years out of 10, after May 14 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 18 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: 138 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 14First frost ~Oct 1Frost season at Keene, NHSpring: a frost after April 30 in 9 years out of 10, after May 14 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 18 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: 138 days.JFMAMJJASONDLast frost ~May 14First 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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 28September 18
50% (typical)May 14October 1
90% (likely)April 30October 14
Frost-free season (32°F, 50% chance)
138 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 11 (3 days earlier than the 30-year normal), typical first fall frost October 3 (2 days later). Frost-free season 142 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 Keene: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 28, 20% May 23, 30% May 19, 40% May 16, 50% May 14, 60% May 11, 70% May 8, 80% May 4, 90% April 30. Observed last spring frost in recent years: 2021 May 8, 2022 May 11, 2023 May 26, 2024 April 28, 2025 May 12, 2026 May 12.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 28May 14Apr 302021: May 82022: May 112023: May 262024: April 282025: May 122026: May 12Fall at Keene: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 23, 30% September 26, 40% September 29, 50% October 1, 60% October 3, 70% October 5, 80% October 9, 90% October 14. Observed first fall frost in recent years: 2021 October 24, 2022 September 30, 2023 October 31, 2024 October 13, 2025 September 21.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 18Oct 1Oct 142021: October 242022: September 302023: October 312024: October 132025: 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 8October 24
2022May 11September 30
2023May 26October 31
2024April 28October 13
2025May 12September 21
2026May 12season not over yet

What these dates mean

The 138 days between the 50% dates in Keene bracket the core growing window, from May 14 in spring to October 1 in fall. The 50% dates represent the point at which there is an even chance of a light frost occurring; they are not themselves frost dates but mark the median of the historical record.

In spring, the cautious date for setting out tender crops is May 28, when there is only a 10 % chance of a light frost later, while planting on April 30 carries a 90 % chance and is a gamble. In fall, the cautious date to finish harvesting tender crops is September 18, with a 10 % chance of a light frost earlier, and October 14 is the gamble with a 90 % chance. Hard frost at 28 °F can damage or kill plants that would survive a light frost at 32 °F, so the 50% hard-frost dates of May 2 and October 10 are a tighter threshold for winter risk.

How to read the probabilities

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

  • Spring: "10% after May 28" 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 18" 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 Keene, NHNumbered nearest stations: 1 — Newport, NH — 31 mi; 2 — Amherst, MA — 40 mi; 3 — Nashua, NH — 44 mi; 4 — Concord, NH — 45 mi; 5 — near Manchester, NH — 47 mi.MAVTNYME25 mi · 40 km1. Newport, NH — 31 mi12. Amherst, MA — 40 mi23. Nashua, NH — 44 mi34. Concord, NH — 45 mi45. near Manchester, NH — 47 mi5
  1. Newport, NH 31 mi (50 km)
  2. Amherst, MA 40 mi (64 km)
  3. Nashua, NH 44 mi (71 km)
  4. Concord, NH 45 mi (73 km)
  5. near Manchester, NH 47 mi (76 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 42.9389, -72.3247.