U.S. Frost Dates by Weather Station

NOAA station USW00024131 · Idaho

Frost Dates for Boise (Air Terminal), ID

NOAA weather station Boise Air Terminal (USW00024131), Idaho · elevation 2814 ft (858 m) · hardiness zone 7b*

  • Lower-risk planting dateafter May 9only 1 spring in 10 still has a frost later
  • Typical last frostApril 2450% chance of a frost after it
  • Typical first fall frostOctober 2150% chance of a frost before it
  • Frost-free season179 daystypical year, 32°F
  • Hardiness zone7bcalculated*

The year at a glance

Frost season at Boise (Air Terminal), IDSpring: a frost after April 4 in 9 years out of 10, after April 24 in half of the years, after May 9 in 1 year out of 10. Fall: the first frost comes before October 5 in 1 year out of 10, before October 21 in half of the years, before November 5 in 9 years out of 10. Typical frost-free season: 179 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 24First frost ~Oct 21Frost season at Boise (Air Terminal), IDSpring: a frost after April 4 in 9 years out of 10, after April 24 in half of the years, after May 9 in 1 year out of 10. Fall: the first frost comes before October 5 in 1 year out of 10, before October 21 in half of the years, before November 5 in 9 years out of 10. Typical frost-free season: 179 days.JFMAMJJASONDLast frost ~Apr 24First frost ~Oct 21
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 9October 5
50% (typical)April 24October 21
90% (likely)April 4November 5
Frost-free season (32°F, 50% chance)
179 days
Hard frost (28°F), last in spring, 50% chance after
April 2
Hard frost (28°F), first in fall, 50% chance before
October 31

The last 15 years (2006–2020 normals)

Typical last frost April 21 (3 days earlier than the 30-year normal), typical first fall frost October 23 (2 days later). Frost-free season 187 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 Boise (Air Terminal): chance of a frost after this dateSpring, chance of a frost after the date: 10% May 9, 20% May 4, 30% April 30, 40% April 27, 50% April 24, 60% April 21, 70% April 17, 80% April 12, 90% April 4. Observed last spring frost in recent years: 2021 April 12, 2022 May 10, 2023 April 20, 2024 April 30, 2025 April 4, 2026 April 17.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 9Apr 24Apr 42021: April 122022: May 102023: April 202024: April 302025: April 42026: April 17Fall at Boise (Air Terminal): chance of a frost before this dateFall, chance of a frost before the date: 10% October 5, 20% October 10, 30% October 14, 40% October 18, 50% October 21, 60% October 24, 70% October 27, 80% October 31, 90% November 5. Observed first fall frost in recent years: 2021 October 14, 2022 October 24, 2023 October 28, 2024 October 29, 2025 October 30.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 5Oct 21Nov 52021: October 142022: October 242023: October 282024: October 292025: October 30
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
2021April 12October 14
2022May 10October 24
2023April 20October 28
2024April 30October 29
2025April 4October 30
2026April 17season not over yet

What these dates mean

October 5 is the cautious fall date for finishing the harvest in Boise (Air Terminal), when there is only a 10 % chance that a light frost has arrived. The median 32 °F dates—April 24 in spring and October 21 in fall—represent the point at which a light frost is as likely as not; they are not frost dates themselves but simply a statistical midpoint for the 27-year record. Gardeners who want to reduce risk place tender crops outdoors after the cautious spring date of May 9, which carries a 10 % chance of a later frost, and pull them in by the cautious fall date of October 5. The hard-frost median dates are April 2 and October 31, and a hard frost at 28 °F can damage plants that survive a light frost because the colder temperature is capable of killing tissue that a 32 °F frost merely chills.

How to read the probabilities

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

  • Spring: "10% after May 9" 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 October 5" 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 Boise (Air Terminal), IDNumbered nearest stations: 1 — near Hidden Spring, ID — 12 mi; 2 — Emmett, ID — 23 mi; 3 — near Murphy, ID — 23 mi; 4 — Garden Valley, ID — 39 mi; 5 — Payette, ID — 49 mi.IDOR25 mi · 40 km1. near Hidden Spring, ID — 12 mi12. Emmett, ID — 23 mi23. near Murphy, ID — 23 mi34. Garden Valley, ID — 39 mi45. Payette, ID — 49 mi5
  1. near Hidden Spring, ID 12 mi (19 km)
  2. Emmett, ID 23 mi (37 km)
  3. near Murphy, ID 23 mi (38 km)
  4. Garden Valley, ID 39 mi (63 km)
  5. Payette, ID 49 mi (79 km)

Sources

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

Station coordinates: 43.5667, -116.2406.