U.S. Frost Dates by Weather Station

NOAA station USC00456789 · Washington

Frost Dates for Pullman, WA

NOAA weather station Pullman 2 NW (USC00456789), Washington · elevation 2515 ft (767 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 650% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Pullman, WASpring: a frost after April 22 in 9 years out of 10, after May 6 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 9 in 1 year out of 10, before September 29 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 6First frost ~Sep 29Frost season at Pullman, WASpring: a frost after April 22 in 9 years out of 10, after May 6 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 9 in 1 year out of 10, before September 29 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 143 days.JFMAMJJASONDLast frost ~May 6First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 25September 9
50% (typical)May 6September 29
90% (likely)April 22October 15
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
April 19
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 5 (1 day earlier than the 30-year normal), typical first fall frost October 1 (2 days later). Frost-free season 149 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 Pullman: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 18, 30% May 13, 40% May 10, 50% May 6, 60% May 3, 70% April 30, 80% April 27, 90% April 22. Observed last spring frost in recent years: 2021 May 9, 2022 May 10, 2023 April 20, 2024 May 2, 2025 May 5, 2026 April 26.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 6Apr 222021: May 92022: May 102023: April 202024: May 22025: May 52026: April 26Fall at Pullman: chance of a frost before this dateFall, chance of a frost before the date: 10% September 9, 20% September 16, 30% September 22, 40% September 27, 50% September 29, 60% October 2, 70% October 5, 80% October 9, 90% October 15. Observed first fall frost in recent years: 2021 October 7, 2022 October 26, 2023 October 26, 2024 September 30, 2025 October 14.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Nov 1Sep 9Sep 29Oct 152021: October 72022: October 262023: October 262024: September 302025: October 14
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 9October 7
2022May 10October 26
2023April 20October 26
2024May 2September 30
2025May 5October 14
2026April 26season not over yet

What these dates mean

The 143 days between the 32°F 50% dates in Pullman—May 6 and September 29—frame the stretch when light-frost risk is balanced. On May 6 there is a 50% chance of a frost later than this date, and on September 29 there is a 50% chance of a frost earlier than this date. These probabilities are drawn from the 29-year record (1991–2020) for this station.

For a cautious spring plan the station’s 10 %-chance date of May 25 is used to set out tender crops, while the cautious fall date of September 9 marks when there is only a 10 % chance a frost has arrived earlier. Hard frosts at 28 °F are more damaging than light frosts at 32 °F, with median dates of April 19 and October 12. Because a hard frost can freeze plant tissues that survive a light frost, it is the more critical threshold.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 9" 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 Pullman, WANumbered nearest stations: 1 — near Lewiston, ID — 28 mi; 2 — St. John, WA — 30 mi; 3 — Lacrosse, WA — 33 mi; 4 — near Orofino, ID — 45 mi; 5 — Saint Maries, ID — 48 mi.ID25 mi · 40 km1. near Lewiston, ID — 28 mi12. St. John, WA — 30 mi23. Lacrosse, WA — 33 mi34. near Orofino, ID — 45 mi45. Saint Maries, ID — 48 mi5
  1. near Lewiston, ID 28 mi (45 km)
  2. St. John, WA 30 mi (48 km)
  3. Lacrosse, WA 33 mi (53 km)
  4. near Orofino, ID 45 mi (72 km)
  5. Saint Maries, ID 48 mi (77 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: 46.7603, -117.1861.