U.S. Frost Dates by Weather Station

NOAA station USC00457267 · Washington

Frost Dates for St. John, WA

NOAA weather station St. John (USC00457267), Washington · elevation 1952 ft (595 m) · hardiness zone 7a*

  • Lower-risk planting dateafter May 15only 1 spring in 10 still has a frost later
  • Typical last frostApril 2950% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season161 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season at St. John, WASpring: a frost after April 9 in 9 years out of 10, after April 29 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 4 in half of the years, before October 23 in 9 years out of 10. Typical frost-free season: 161 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 29First frost ~Oct 4Frost season at St. John, WASpring: a frost after April 9 in 9 years out of 10, after April 29 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 4 in half of the years, before October 23 in 9 years out of 10. Typical frost-free season: 161 days.JFMAMJJASONDLast frost ~Apr 29First frost ~Oct 4
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)May 15September 19
50% (typical)April 29October 4
90% (likely)April 9October 23
Frost-free season (32°F, 50% chance)
161 days
Hard frost (28°F), last in spring, 50% chance after
April 5
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost April 29 (same as the 30-year normal), typical first fall frost October 8 (4 days later). Frost-free season 161 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 St. John: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 15, 20% May 9, 30% May 5, 40% May 1, 50% April 29, 60% April 26, 70% April 22, 80% April 17, 90% April 9.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 15Apr 29Apr 9Fall at St. John: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 26, 30% September 30, 40% October 2, 50% October 4, 60% October 8, 70% October 12, 80% October 18, 90% October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 19Oct 4Oct 23
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.

What these dates mean

The cautious fall date in St. John is September 19, when there is only a 10 % chance that a light frost has arrived earlier, marking a prudent time to finish harvesting tender crops.

The 50% dates are April 29 in spring and October 4 in fall; each indicates the point where a 32°F light frost is equally likely to have occurred later (spring) or earlier (fall). For a low-risk plan, tender crops are typically set out after the cautious spring date of May 15 and harvested before the cautious fall date of September 19. Between the two 32°F 50% dates there are 161 days, derived from 28 years of records.

Hard frosts at 28°F, noted on April 5 in spring and October 20 in fall, can cause far greater damage to plants than the milder 32°F light frosts.

How to read the probabilities

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

  • Spring: "10% after May 15" 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 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 St. John, WANumbered nearest stations: 1 — Lacrosse, WA — 24 mi; 2 — Pullman, WA — 30 mi; 3 — Spokane, WA — 37 mi; 4 — Ritzville, WA — 37 mi; 5 — Davenport, WA — 47 mi.ID25 mi · 40 km1. Lacrosse, WA — 24 mi12. Pullman, WA — 30 mi23. Spokane, WA — 37 mi34. Ritzville, WA — 37 mi45. Davenport, WA — 47 mi5
  1. Lacrosse, WA 24 mi (38 km)
  2. Pullman, WA 30 mi (48 km)
  3. Spokane, WA 37 mi (59 km)
  4. Ritzville, WA 37 mi (59 km)
  5. Davenport, WA 47 mi (76 km)

Sources

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

Station coordinates: 47.0933, -117.5878.