U.S. Frost Dates by Weather Station

NOAA station USC00102159 · Idaho

Frost Dates for Cottonwood, ID

NOAA weather station Cottonwood 2 WSW (USC00102159), Idaho · elevation 3945 ft (1202 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 26only 1 spring in 10 still has a frost later
  • Typical last frostMay 650% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season156 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Cottonwood, IDSpring: a frost after April 22 in 9 years out of 10, after May 6 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 13 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 156 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 6First frost ~Oct 13Frost season at Cottonwood, IDSpring: a frost after April 22 in 9 years out of 10, after May 6 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 13 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 156 days.JFMAMJJASONDLast frost ~May 6First frost ~Oct 13
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 26September 28
50% (typical)May 6October 13
90% (likely)April 22October 27
Frost-free season (32°F, 50% chance)
156 days
Hard frost (28°F), last in spring, 50% chance after
April 21
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost May 6 (same as the 30-year normal), typical first fall frost October 14 (1 day later). Frost-free season 161 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 Cottonwood: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 19, 30% May 15, 40% May 10, 50% May 6, 60% May 3, 70% April 30, 80% April 27, 90% April 22. Observed last spring frost in recent years: 2022 May 13, 2023 April 24, 2024 May 20, 2025 May 19, 2026 May 17.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 6Apr 222022: May 132023: April 242024: May 202025: May 192026: May 17Fall at Cottonwood: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 3, 30% October 6, 40% October 9, 50% October 13, 60% October 15, 70% October 18, 80% October 22, 90% October 27. Observed first fall frost in recent years: 2022 October 23, 2023 October 26, 2024 October 18, 2025 October 27.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 13Oct 272022: October 232023: October 262024: October 182025: October 27
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
2021incomplete recordincomplete record
2022May 13October 23
2023April 24October 26
2024May 20October 18
2025May 19October 27
2026May 17season not over yet

What these dates mean

The cautious spring date for Cottonwood is May 26, when there is only a 10 % chance of a light frost later, so a gardener can plan to set out tender crops after that day. In the fall the cautious date is September 28, with only a 10 % chance that a light frost has arrived earlier, marking the latest reasonable time to finish harvesting tender crops.

The 50% dates indicate even odds of a frost. The 50% date for light frost in spring is May 6 and the 50% date for light frost in fall is October 13; these dates are not frost thresholds but points where a frost is as likely as not. The 50% hard-frost date in spring is April 21 and the 50% hard-frost date in fall is October 24, showing when a 28 °F freeze has a 50 % chance of occurring.

A hard frost at 28 °F can harm plant tissue more severely than a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 26" 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 28" 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 Cottonwood, IDNumbered nearest stations: 1 — Nezperce, ID — 15 mi; 2 — near Orofino, ID — 33 mi; 3 — near Lewiston, ID — 38 mi; 4 — Pullman, WA — 63 mi; 5 — Dayton, WA — 79 mi.WAID25 mi · 40 km1. Nezperce, ID — 15 mi12. near Orofino, ID — 33 mi23. near Lewiston, ID — 38 mi34. Pullman, WA — 63 mi45. Dayton, WA — 79 mi5
  1. Nezperce, ID 15 mi (25 km)
  2. near Orofino, ID 33 mi (52 km)
  3. near Lewiston, ID 38 mi (61 km)
  4. Pullman, WA 63 mi (101 km)
  5. Dayton, WA 79 mi (128 km)

Sources

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

Station coordinates: 46.0336, -116.3919.