U.S. Frost Dates by Weather Station

NOAA station USC00456534 · Washington

Frost Dates for Plain, WA

NOAA weather station Plain (USC00456534), Washington · elevation 1936 ft (590 m) · hardiness zone 6b*

  • Lower-risk planting dateafter June 13only 1 spring in 10 still has a frost later
  • Typical last frostMay 2250% chance of a frost after it
  • Typical first fall frostSeptember 2250% chance of a frost before it
  • Frost-free season121 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Plain, WASpring: a frost after May 2 in 9 years out of 10, after May 22 in half of the years, after June 13 in 1 year out of 10. Fall: the first frost comes before September 7 in 1 year out of 10, before September 22 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 121 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 22First frost ~Sep 22Frost season at Plain, WASpring: a frost after May 2 in 9 years out of 10, after May 22 in half of the years, after June 13 in 1 year out of 10. Fall: the first frost comes before September 7 in 1 year out of 10, before September 22 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 121 days.JFMAMJJASONDLast frost ~May 22First 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 13September 7
50% (typical)May 22September 22
90% (likely)May 2October 4
Frost-free season (32°F, 50% chance)
121 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 19 (3 days earlier than the 30-year normal), typical first fall frost September 23 (1 day later). Frost-free season 126 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 Plain: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 13, 20% June 5, 30% May 31, 40% May 26, 50% May 22, 60% May 18, 70% May 14, 80% May 9, 90% May 2. Observed last spring frost in recent years: 2021 May 29, 2022 May 20, 2024 May 31, 2025 May 19, 2026 May 17.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 13May 22May 22021: May 292022: May 202024: May 312025: May 192026: May 17Fall at Plain: chance of a frost before this dateFall, chance of a frost before the date: 10% September 7, 20% September 12, 30% September 16, 40% September 19, 50% September 22, 60% September 25, 70% September 27, 80% September 30, 90% October 4. Observed first fall frost in recent years: 2021 September 16, 2022 September 21.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 7Sep 22Oct 42021: September 162022: 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 29September 16
2022May 20September 21
2023incomplete recordincomplete record
2024May 31incomplete record
2025May 19incomplete record
2026May 17season not over yet

What these dates mean

The 121 days between the 50% dates in Plain — May 22 and September 22 — mark the span in which a gardener faces an even chance of a light frost, later in spring and earlier in fall. These median dates show that on any given year there is a 50 % probability of a light frost occurring after May 22 and a 50 % probability of one occurring before September 22.

For a cautious approach, tender crops are usually set out after the June 13 date, which carries only a 10 % chance of a light frost later, while harvesting is completed before the September 7 date, which has a 10 % chance of a light frost earlier. Planting as early as May 2 or keeping crops until October 4 involves a 90 % chance of frost and should be considered a gamble rather than a reliable option.

A hard frost at 28 °F matters more than a light frost at 32 °F because it can damage plant tissue that would survive the milder temperature.

How to read the probabilities

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

  • Spring: "10% after June 13" 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 7" 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 Plain, WANumbered nearest stations: 1 — near Entiat, WA — 16 mi; 2 — Wenatchee, WA — 29 mi; 3 — Chelan, WA — 30 mi; 4 — Wenatchee (Pangborn Airport), WA — 34 mi; 5 — Stehekin, WA — 39 mi.WA25 mi · 40 km1. near Entiat, WA — 16 mi12. Wenatchee, WA — 29 mi23. Chelan, WA — 30 mi34. Wenatchee (Pangborn Airport), WA — 34 mi45. Stehekin, WA — 39 mi5
  1. near Entiat, WA 16 mi (26 km)
  2. Wenatchee, WA 29 mi (47 km)
  3. Chelan, WA 30 mi (48 km)
  4. Wenatchee (Pangborn Airport), WA 34 mi (54 km)
  5. Stehekin, WA 39 mi (63 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: 47.785, -120.6456.