U.S. Frost Dates by Weather Station

NOAA station USC00107386 · Idaho

Frost Dates for Priest River, ID

NOAA weather station Priest River Experiment Station (USC00107386), Idaho · elevation 2371 ft (723 m) · hardiness zone 6a*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostSeptember 1350% chance of a frost before it
  • Frost-free season114 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Priest River, IDSpring: a frost after May 6 in 9 years out of 10, after May 20 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 1 in 1 year out of 10, before September 13 in half of the years, before September 30 in 9 years out of 10. Typical frost-free season: 114 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Sep 13Frost season at Priest River, IDSpring: a frost after May 6 in 9 years out of 10, after May 20 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 1 in 1 year out of 10, before September 13 in half of the years, before September 30 in 9 years out of 10. Typical frost-free season: 114 days.JFMAMJJASONDLast frost ~May 20First frost ~Sep 13
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)June 4September 1
50% (typical)May 20September 13
90% (likely)May 6September 30
Frost-free season (32°F, 50% chance)
114 days
Hard frost (28°F), last in spring, 50% chance after
May 4
Hard frost (28°F), first in fall, 50% chance before
September 28

The last 15 years (2006–2020 normals)

Typical last frost May 18 (2 days earlier than the 30-year normal), typical first fall frost September 11 (2 days earlier). Frost-free season 116 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 Priest River: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 30, 30% May 27, 40% May 24, 50% May 20, 60% May 17, 70% May 14, 80% May 11, 90% May 6. Observed last spring frost in recent years: 2021 May 21, 2022 May 23, 2023 April 28, 2024 June 17.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 20May 62021: May 212022: May 232023: April 282024: June 17Fall at Priest River: chance of a frost before this dateFall, chance of a frost before the date: 10% September 1, 20% September 3, 30% September 7, 40% September 9, 50% September 13, 60% September 16, 70% September 19, 80% September 23, 90% September 30. Observed first fall frost in recent years: 2021 August 31, 2022 October 12, 2023 October 1, 2024 September 21.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 1Sep 13Sep 302021: August 312022: October 122023: October 12024: September 21
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 21August 31
2022May 23October 12
2023April 28October 1
2024June 17September 21
2025incomplete recordno data
2026no dataseason not over yet

What these dates mean

Setting out tender crops on the early spring date of May 6 in Priest River carries a 90 % chance that a light frost will occur later, making it a gamble for growers. The 50 % spring date of May 20 indicates an even-odds chance of a light frost later than that day, while the 50 % hard-frost date of May 4 marks the point at which a 28 °F frost is as likely as not.

For a cautious plan, the spring light-frost date of June 4 is used, because only a 10 % chance of frost remains after it. In the autumn, the cautious date to finish harvesting tender crops is September 1, when the probability of a light frost earlier is just a 10 % chance. The median autumn light-frost date is September 13, and the hard-frost median is September 28.

A hard frost at 28 °F can damage plants that would otherwise survive a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after June 4" 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 1" 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 Priest River, IDNumbered nearest stations: 1 — Bonners Ferry, ID — 34 mi; 2 — Cabinet Gorge, ID — 40 mi; 3 — Chewelah, WA — 42 mi; 4 — Boundary Dam, WA — 50 mi; 5 — Northport, WA — 59 mi.WAIDMT25 mi · 40 km1. Bonners Ferry, ID — 34 mi12. Cabinet Gorge, ID — 40 mi23. Chewelah, WA — 42 mi34. Boundary Dam, WA — 50 mi45. Northport, WA — 59 mi5
  1. Bonners Ferry, ID 34 mi (54 km)
  2. Cabinet Gorge, ID 40 mi (65 km)
  3. Chewelah, WA 42 mi (68 km)
  4. Boundary Dam, WA 50 mi (81 km)
  5. Northport, WA 59 mi (95 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.3511, -116.8353.