U.S. Frost Dates by Weather Station

NOAA station USC00108062 · Idaho

Frost Dates for Saint Maries, ID

NOAA weather station Saint Maries (USC00108062), Idaho · elevation 2151 ft (656 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 18only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season152 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Saint Maries, IDSpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 4 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 152 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 4Frost season at Saint Maries, IDSpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 4 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 152 days.JFMAMJJASONDLast frost ~May 3First 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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 18September 18
50% (typical)May 3October 4
90% (likely)April 20October 20
Frost-free season (32°F, 50% chance)
152 days
Hard frost (28°F), last in spring, 50% chance after
April 14
Hard frost (28°F), first in fall, 50% chance before
October 19

The last 15 years (2006–2020 normals)

Typical last frost May 2 (1 day earlier than the 30-year normal), typical first fall frost October 3 (1 day earlier). Frost-free season 155 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 Saint Maries: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 18, 20% May 13, 30% May 10, 40% May 7, 50% May 3, 60% May 1, 70% April 29, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 May 5.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 18May 3Apr 202021: May 5Fall at Saint Maries: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 24, 30% September 27, 40% October 1, 50% October 4, 60% October 6, 70% October 10, 80% October 14, 90% October 20.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 18Oct 4Oct 20
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 5incomplete record
2022incomplete recordincomplete record
2023incomplete recordincomplete record
2024incomplete recordincomplete record
2025incomplete recordincomplete record
2026incomplete recordseason not over yet

What these dates mean

May 18 is the cautious spring date for Saint Maries, allowing a gardener to set out tender crops with only a 10% chance of a later frost. The 50% date is May 3, representing an even chance that a frost will still occur later, while the April 20 date carries a 90% chance and is a gamble for early planting.

In the fall the cautious date is September 18, when there is only a 10% chance that a frost has already arrived, giving a reliable point to finish harvesting tender crops. The 50% date is October 4, indicating a 50% chance of a frost earlier than this date, and the October 20 date involves a 90% chance and is risky for late crops. Hard frost at 28 °F can cause far more severe damage than a light frost at 32 °F, so the 50% hard-frost dates of April 14 and October 19 are especially important for protecting plants.

How to read the probabilities

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

  • Spring: "10% after May 18" 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 18" 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 Saint Maries, IDNumbered nearest stations: 1 — Kellogg, ID — 26 mi; 2 — Pullman, WA — 48 mi; 3 — Spokane, WA — 49 mi; 4 — St. John, WA — 50 mi; 5 — near Orofino, ID — 58 mi.IDWAMT25 mi · 40 km1. Kellogg, ID — 26 mi12. Pullman, WA — 48 mi23. Spokane, WA — 49 mi34. St. John, WA — 50 mi45. near Orofino, ID — 58 mi5
  1. Kellogg, ID 26 mi (42 km)
  2. Pullman, WA 48 mi (77 km)
  3. Spokane, WA 49 mi (79 km)
  4. St. John, WA 50 mi (80 km)
  5. near Orofino, ID 58 mi (93 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: 47.3164, -116.5789.