U.S. Frost Dates by Weather Station

NOAA station USC00452157 · Washington

Frost Dates for Diablo Dam, WA

NOAA weather station Diablo Dam (USC00452157), Washington · elevation 891 ft (272 m) · hardiness zone 8a*

  • Lower-risk planting dateafter May 1only 1 spring in 10 still has a frost later
  • Typical last frostApril 1050% chance of a frost after it
  • Typical first fall frostNovember 150% chance of a frost before it
  • Frost-free season203 daystypical year, 32°F
  • Hardiness zone8acalculated*

The year at a glance

Frost season at Diablo Dam, WASpring: a frost after March 22 in 9 years out of 10, after April 10 in half of the years, after May 1 in 1 year out of 10. Fall: the first frost comes before October 19 in 1 year out of 10, before November 1 in half of the years, before November 20 in 9 years out of 10. Typical frost-free season: 203 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 10First frost ~Nov 1Frost season at Diablo Dam, WASpring: a frost after March 22 in 9 years out of 10, after April 10 in half of the years, after May 1 in 1 year out of 10. Fall: the first frost comes before October 19 in 1 year out of 10, before November 1 in half of the years, before November 20 in 9 years out of 10. Typical frost-free season: 203 days.JFMAMJJASONDLast frost ~Apr 10First frost ~Nov 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.Today

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 1October 19
50% (typical)April 10November 1
90% (likely)March 22November 20
Frost-free season (32°F, 50% chance)
203 days
Hard frost (28°F), last in spring, 50% chance after
March 13
Hard frost (28°F), first in fall, 50% chance before
November 20

The last 15 years (2006–2020 normals)

Typical last frost April 12 (2 days later than the 30-year normal), typical first fall frost November 1. Frost-free season 200 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 Diablo Dam: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 1, 20% April 25, 30% April 20, 40% April 15, 50% April 10, 60% April 6, 70% April 3, 80% March 30, 90% March 22. Observed last spring frost in recent years: 2021 April 15, 2022 April 30, 2023 April 20, 2024 March 15, 2025 April 14, 2026 March 31.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 1Apr 10Mar 222021: April 152022: April 302023: April 202024: March 152025: April 142026: March 31Fall at Diablo Dam: chance of a frost before this dateFall, chance of a frost before the date: 10% October 19, 20% October 24, 30% October 28, 40% October 30, 50% November 1, 60% November 5, 70% November 8, 80% November 13, 90% November 20. Observed first fall frost in recent years: 2021 October 12, 2022 November 3, 2023 October 26, 2024 November 17, 2025 November 30.Fall: first frostChance of a frost before this date10%50%90%Nov 1Dec 1Oct 19Nov 1Nov 202021: October 122022: November 32023: October 262024: November 172025: November 30
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
2021April 15October 12
2022April 30November 3
2023April 20October 26
2024March 15November 17
2025April 14November 30
2026March 31season not over yet

What these dates mean

The 203 days between the 32 °F 50 % dates, April 10 and November 1, define the span in which a light frost is equally likely to have occurred or not. For a gardener this median point marks the middle of the period where frost risk balances, while dates outside it tilt toward higher or lower chances.

In spring the cautious date for setting out tender crops is May 1, when only a 10 % chance of a later light frost remains; planting on March 22 carries a 90 % chance of a frost and is a gamble. In fall the cautious date to finish harvesting tender crops is October 19, with a 10 % chance that a light frost has already arrived, whereas aiming for November 20 involves a 90 % chance of an earlier frost. The 50 % hard-frost dates are March 13 and November 20, and hard frost at 28 °F can damage plant tissues that survive a light frost at 32 °F, making it a more serious threat.

How to read the probabilities

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

  • Spring: "10% after May 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 October 19" 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 Diablo Dam, WANumbered nearest stations: 1 — Ross Dam, WA — 3 mi; 2 — Newhalem, WA — 5 mi; 3 — Upper Baker Dam, WA — 25 mi; 4 — Concrete PPL Fish Station, WA — 30 mi; 5 — Stehekin, WA — 32 mi.WA25 mi · 40 km1. Ross Dam, WA — 3 mi12. Newhalem, WA — 5 mi23. Upper Baker Dam, WA — 25 mi34. Concrete PPL Fish Station, WA — 30 mi45. Stehekin, WA — 32 mi5
  1. Ross Dam, WA 3 mi (5 km)
  2. Newhalem, WA 5 mi (8 km)
  3. Upper Baker Dam, WA 25 mi (41 km)
  4. Concrete PPL Fish Station, WA 30 mi (48 km)
  5. Stehekin, WA 32 mi (51 km)

Sources

* Hardiness zone 8a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.7142, -121.1431.