U.S. Frost Dates by Weather Station

NOAA station USC00457185 · Washington

Frost Dates for Ross Dam, WA

NOAA weather station Ross Dam (USC00457185), Washington · elevation 1236 ft (377 m) · hardiness zone 7b*

  • Lower-risk planting dateafter April 30only 1 spring in 10 still has a frost later
  • Typical last frostApril 850% chance of a frost after it
  • Typical first fall frostNovember 1050% chance of a frost before it
  • Frost-free season214 daystypical year, 32°F
  • Hardiness zone7bcalculated*

The year at a glance

Frost season at Ross Dam, WASpring: a frost after March 16 in 9 years out of 10, after April 8 in half of the years, after April 30 in 1 year out of 10. Fall: the first frost comes before October 26 in 1 year out of 10, before November 10 in half of the years, before November 25 in 9 years out of 10. Typical frost-free season: 214 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 8First frost ~Nov 10Frost season at Ross Dam, WASpring: a frost after March 16 in 9 years out of 10, after April 8 in half of the years, after April 30 in 1 year out of 10. Fall: the first frost comes before October 26 in 1 year out of 10, before November 10 in half of the years, before November 25 in 9 years out of 10. Typical frost-free season: 214 days.JFMAMJJASONDLast frost ~Apr 8First frost ~Nov 10
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 30October 26
50% (typical)April 8November 10
90% (likely)March 16November 25
Frost-free season (32°F, 50% chance)
214 days
Hard frost (28°F), last in spring, 50% chance after
March 11
Hard frost (28°F), first in fall, 50% chance before
November 25

The last 15 years (2006–2020 normals)

Typical last frost April 4 (4 days earlier than the 30-year normal), typical first fall frost November 11 (1 day later). Frost-free season 215 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 Ross Dam: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 30, 20% April 22, 30% April 16, 40% April 12, 50% April 8, 60% April 4, 70% March 31, 80% March 25, 90% March 16. Observed last spring frost in recent years: 2021 April 13, 2022 April 28, 2023 April 19, 2024 April 23, 2025 April 13, 2026 March 31.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Apr 30Apr 8Mar 162021: April 132022: April 282023: April 192024: April 232025: April 132026: March 31Fall at Ross Dam: chance of a frost before this dateFall, chance of a frost before the date: 10% October 26, 20% October 31, 30% November 4, 40% November 6, 50% November 10, 60% November 13, 70% November 17, 80% November 21, 90% November 25. Observed first fall frost in recent years: 2021 October 12, 2022 November 3, 2023 October 27, 2024 November 17, 2025 November 30.Fall: first frostChance of a frost before this date10%50%90%Nov 1Dec 1Oct 26Nov 10Nov 252021: October 122022: November 32023: October 272024: 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 13October 12
2022April 28November 3
2023April 19October 27
2024April 23November 17
2025April 13November 30
2026March 31season not over yet

What these dates mean

The 214 days between the 50% dates in Ross Dam define the window when the average risk of a light frost is roughly even. The 50% spring date, April 8, marks the point at which a light frost is as likely to occur later as not, while the 50% fall date, November 10, marks the opposite odds for a frost arriving earlier. Likewise, the 50% hard-frost dates—March 11 in spring and November 25 in fall—represent the median chance of temperatures dropping to 28 °F.

For a cautious planting schedule, tender crops are best set out after the April 30 date, which carries only a 10 % chance of a later light frost, and are recommended to be harvested by October 26, when there is only a 10 % chance that a light frost has already begun. Planting on March 16 or waiting until November 25 involves a 90 % chance of frost and is therefore a gamble. A hard frost at 28 °F can damage plants more severely than a light frost at 32 °F because it reaches a lower temperature threshold.

How to read the probabilities

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

  • Spring: "10% after April 30" 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 26" 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 Ross Dam, WANumbered nearest stations: 1 — Diablo Dam, WA — 3 mi; 2 — Newhalem, WA — 9 mi; 3 — Upper Baker Dam, WA — 29 mi; 4 — Stehekin, WA — 30 mi; 5 — Mazama, WA — 31 mi.WA25 mi · 40 km1. Diablo Dam, WA — 3 mi12. Newhalem, WA — 9 mi23. Upper Baker Dam, WA — 29 mi34. Stehekin, WA — 30 mi45. Mazama, WA — 31 mi5
  1. Diablo Dam, WA 3 mi (5 km)
  2. Newhalem, WA 9 mi (14 km)
  3. Upper Baker Dam, WA 29 mi (46 km)
  4. Stehekin, WA 30 mi (49 km)
  5. Mazama, WA 31 mi (49 km)

Sources

* Hardiness zone 7b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.7272, -121.0722.