U.S. Frost Dates by Weather Station

NOAA station USC00459376 · Washington

Frost Dates for Winthrop, WA

NOAA weather station Winthrop 1 WSW (USC00459376), Washington · elevation 1749 ft (533 m) · hardiness zone 5b*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostSeptember 2250% chance of a frost before it
  • Frost-free season127 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Winthrop, WASpring: a frost after April 30 in 9 years out of 10, after May 15 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 10 in 1 year out of 10, before September 22 in half of the years, before October 2 in 9 years out of 10. Typical frost-free season: 127 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 22Frost season at Winthrop, WASpring: a frost after April 30 in 9 years out of 10, after May 15 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 10 in 1 year out of 10, before September 22 in half of the years, before October 2 in 9 years out of 10. Typical frost-free season: 127 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 22
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 1September 10
50% (typical)May 15September 22
90% (likely)April 30October 2
Frost-free season (32°F, 50% chance)
127 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 3

The last 15 years (2006–2020 normals)

Typical last frost May 12 (3 days earlier than the 30-year normal), typical first fall frost September 23 (1 day later). Frost-free season 131 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 Winthrop: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 27, 30% May 22, 40% May 19, 50% May 15, 60% May 13, 70% May 9, 80% May 6, 90% April 30. Observed last spring frost in recent years: 2021 May 19, 2022 May 13, 2023 April 25, 2024 June 16, 2025 May 9, 2026 June 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 15Apr 302021: May 192022: May 132023: April 252024: June 162025: May 92026: June 19Fall at Winthrop: chance of a frost before this dateFall, chance of a frost before the date: 10% September 10, 20% September 14, 30% September 17, 40% September 19, 50% September 22, 60% September 24, 70% September 27, 80% September 29, 90% October 2. Observed first fall frost in recent years: 2021 October 1, 2022 October 16, 2023 September 29, 2024 September 28, 2025 October 3.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 10Sep 22Oct 22021: October 12022: October 162023: September 292024: September 282025: October 3
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 19October 1
2022May 13October 16
2023April 25September 29
2024June 16September 28
2025May 9October 3
2026June 19season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 30 in Winthrop carries a 90 % chance of a frost later than that date. The 50 % date in spring is May 15, which indicates a 50 % chance of a frost later than this date. In fall, the 50 % date is September 22, representing a 50 % chance of a frost earlier than this date.

A cautious plan for tender crops would use the June 1 spring date, which has only a 10 % chance of a frost later than it, and the September 10 fall date, which has a 10 % chance of a frost earlier than it. The 50 % hard-frost dates are May 1 in spring and October 3 in fall; a hard frost at 28 °F can injure plants that survive 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 June 1" 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 10" 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 Winthrop, WANumbered nearest stations: 1 — Mazama, WA — 14 mi; 2 — Stehekin, WA — 26 mi; 3 — near Bridgeport, WA — 41 mi; 4 — Ross Dam, WA — 44 mi; 5 — Chelan, WA — 45 mi.WA25 mi · 40 km1. Mazama, WA — 14 mi12. Stehekin, WA — 26 mi23. near Bridgeport, WA — 41 mi34. Ross Dam, WA — 44 mi45. Chelan, WA — 45 mi5
  1. Mazama, WA 14 mi (23 km)
  2. Stehekin, WA 26 mi (42 km)
  3. near Bridgeport, WA 41 mi (66 km)
  4. Ross Dam, WA 44 mi (71 km)
  5. Chelan, WA 45 mi (72 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: 48.4742, -120.1886.