U.S. Frost Dates by Weather Station

NOAA station USC00101079 · Idaho

Frost Dates for Bonners Ferry, ID

NOAA weather station Bonners Ferry (USC00101079), Idaho · elevation 2075 ft (633 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season154 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Bonners Ferry, IDSpring: a frost after April 16 in 9 years out of 10, after April 30 in half of the years, after May 16 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 19 in 9 years out of 10. Typical frost-free season: 154 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 4Frost season at Bonners Ferry, IDSpring: a frost after April 16 in 9 years out of 10, after April 30 in half of the years, after May 16 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 19 in 9 years out of 10. Typical frost-free season: 154 days.JFMAMJJASONDLast frost ~Apr 30First 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 16September 18
50% (typical)April 30October 4
90% (likely)April 16October 19
Frost-free season (32°F, 50% chance)
154 days
Hard frost (28°F), last in spring, 50% chance after
April 10
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost April 29 (1 day earlier than the 30-year normal), typical first fall frost October 7 (3 days later). Frost-free season 162 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 Bonners Ferry: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 11, 30% May 6, 40% May 3, 50% April 30, 60% April 28, 70% April 25, 80% April 21, 90% April 16. Observed last spring frost in recent years: 2021 May 19, 2022 April 30, 2023 April 24, 2025 April 24, 2026 April 25.Spring: last frostChance of a frost after this date10%50%90%May 1May 16Apr 30Apr 162021: May 192022: April 302023: April 242025: April 242026: April 25Fall at Bonners Ferry: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 23, 30% September 27, 40% October 1, 50% October 4, 60% October 7, 70% October 10, 80% October 14, 90% October 19. Observed first fall frost in recent years: 2021 October 8, 2022 November 6, 2023 October 25, 2025 October 15.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 18Oct 4Oct 192021: October 82022: November 62023: October 252025: October 15
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 19October 8
2022April 30November 6
2023April 24October 25
2024incomplete recordincomplete record
2025April 24October 15
2026April 25season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 16 carries a 90 % chance of a frost later that season, making it a gamble for gardeners in Bonners Ferry. The cautious alternative is May 16, when only a 10 % chance of a later frost remains.

The 50 % date is April 30, indicating an even odds of a light frost on that day, and the 50 % date is October 4, marking an even odds of a light frost in the fall. The median hard-frost date, April 10, and the median hard-frost date, October 16, are the points at which a 50 % chance of a 28 °F frost exists. A hard frost at 28 °F can damage plants that survive a light frost at 32 °F, so it is a more critical threshold.

For a cautious plan, gardeners should aim to set out tender crops after May 16 in spring and finish harvesting tender crops before September 18 in fall.

How to read the probabilities

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

  • Spring: "10% after May 16" 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 Bonners Ferry, IDNumbered nearest stations: 1 — Priest River, ID — 34 mi; 2 — Cabinet Gorge, ID — 43 mi; 3 — Libby Dam (Base), MT — 49 mi; 4 — Boundary Dam, WA — 52 mi; 5 — Northport, WA — 71 mi.IDWAMT25 mi · 40 km1. Priest River, ID — 34 mi12. Cabinet Gorge, ID — 43 mi23. Libby Dam (Base), MT — 49 mi34. Boundary Dam, WA — 52 mi45. Northport, WA — 71 mi5
  1. Priest River, ID 34 mi (54 km)
  2. Cabinet Gorge, ID 43 mi (70 km)
  3. Libby Dam (Base), MT 49 mi (80 km)
  4. Boundary Dam, WA 52 mi (83 km)
  5. Northport, WA 71 mi (114 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: 48.6928, -116.3103.