U.S. Frost Dates by Weather Station

NOAA station USC00455133 · Washington

Frost Dates for Mazama, WA

NOAA weather station Mazama (USC00455133), Washington · elevation 2141 ft (653 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 950% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season142 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Mazama, WASpring: a frost after April 28 in 9 years out of 10, after May 9 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 15 in 1 year out of 10, before September 29 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 142 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 9First frost ~Sep 29Frost season at Mazama, WASpring: a frost after April 28 in 9 years out of 10, after May 9 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 15 in 1 year out of 10, before September 29 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 142 days.JFMAMJJASONDLast frost ~May 9First frost ~Sep 29
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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 24September 15
50% (typical)May 9September 29
90% (likely)April 28October 10
Frost-free season (32°F, 50% chance)
142 days
Hard frost (28°F), last in spring, 50% chance after
April 25
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 6 (3 days earlier than the 30-year normal), typical first fall frost October 1 (2 days later). Frost-free season 146 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 Mazama: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 18, 30% May 14, 40% May 12, 50% May 9, 60% May 7, 70% May 4, 80% May 1, 90% April 28. Observed last spring frost in recent years: 2021 April 27, 2022 May 13, 2023 April 22, 2024 May 3, 2025 April 24, 2026 April 27.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 24May 9Apr 282021: April 272022: May 132023: April 222024: May 32025: April 242026: April 27Fall at Mazama: chance of a frost before this dateFall, chance of a frost before the date: 10% September 15, 20% September 21, 30% September 24, 40% September 27, 50% September 29, 60% October 1, 70% October 3, 80% October 6, 90% October 10. Observed first fall frost in recent years: 2021 October 2, 2022 October 17, 2023 September 29, 2024 October 1, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 15Sep 29Oct 102021: October 22022: October 172023: September 292024: October 12025: October 6
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 27October 2
2022May 13October 17
2023April 22September 29
2024May 3October 1
2025April 24October 6
2026April 27season not over yet

What these dates mean

September 15 marks the cautious fall date in Mazama for finishing the harvest, with only a 10% chance that a light frost has arrived earlier. In spring, the cautious date for setting out tender crops is May 24, when the chance of a light frost later than that date is just 10%.

The 50% light-frost dates are May 9 and September 29; each represents a 50% chance of a frost occurring later (spring) or earlier (fall) than the date. The 50% hard-frost dates are April 25 and October 10, indicating even odds for a 28 °F frost around those days.

Because a hard frost at 28 °F can injure or kill plant tissue more severely than a light frost at 32 °F, it is a more critical threshold for gardeners in this location. The record spans 25 years.

How to read the probabilities

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

  • Spring: "10% after May 24" 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 15" 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 Mazama, WANumbered nearest stations: 1 — Winthrop, WA — 14 mi; 2 — Stehekin, WA — 22 mi; 3 — Ross Dam, WA — 31 mi; 4 — Diablo Dam, WA — 34 mi; 5 — Newhalem, WA — 38 mi.WA25 mi · 40 km1. Winthrop, WA — 14 mi12. Stehekin, WA — 22 mi23. Ross Dam, WA — 31 mi34. Diablo Dam, WA — 34 mi45. Newhalem, WA — 38 mi5
  1. Winthrop, WA 14 mi (23 km)
  2. Stehekin, WA 22 mi (35 km)
  3. Ross Dam, WA 31 mi (49 km)
  4. Diablo Dam, WA 34 mi (54 km)
  5. Newhalem, WA 38 mi (60 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: 48.6008, -120.4275.