U.S. Frost Dates by Weather Station

NOAA station USW00094143 · Idaho

Frost Dates for Idaho Falls 46 W, ID

NOAA weather station Idaho Falls 46 W (USW00094143), Idaho · elevation 4938 ft (1505 m) · hardiness zone 4b*

  • Lower-risk planting dateafter July 1only 1 spring in 10 still has a frost later
  • Typical last frostJune 1150% chance of a frost after it
  • Typical first fall frostSeptember 650% chance of a frost before it
  • Frost-free season89 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Idaho Falls 46 W, IDSpring: a frost after May 20 in 9 years out of 10, after June 11 in half of the years, after July 1 in 1 year out of 10. Fall: the first frost comes before August 24 in 1 year out of 10, before September 6 in half of the years, before September 21 in 9 years out of 10. Typical frost-free season: 89 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 11First frost ~Sep 6Frost season at Idaho Falls 46 W, IDSpring: a frost after May 20 in 9 years out of 10, after June 11 in half of the years, after July 1 in 1 year out of 10. Fall: the first frost comes before August 24 in 1 year out of 10, before September 6 in half of the years, before September 21 in 9 years out of 10. Typical frost-free season: 89 days.JFMAMJJASONDLast frost ~Jun 11First frost ~Sep 6
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.Today

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)July 1August 24
50% (typical)June 11September 6
90% (likely)May 20September 21
Frost-free season (32°F, 50% chance)
89 days
Hard frost (28°F), last in spring, 50% chance after
May 23
Hard frost (28°F), first in fall, 50% chance before
September 18

The last 15 years (2006–2020 normals)

Typical last frost June 12 (1 day later than the 30-year normal), typical first fall frost September 9 (3 days later). Frost-free season 89 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 Idaho Falls 46 W: chance of a frost after this dateSpring, chance of a frost after the date: 10% July 1, 20% June 25, 30% June 20, 40% June 15, 50% June 11, 60% June 7, 70% June 3, 80% May 28, 90% May 20. Observed last spring frost in recent years: 2021 June 11, 2022 June 15, 2023 June 22, 2024 June 20, 2025 June 23, 2026 June 12.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jul 1Jun 11May 202021: June 112022: June 152023: June 222024: June 202025: June 232026: June 12Fall at Idaho Falls 46 W: chance of a frost before this dateFall, chance of a frost before the date: 10% August 24, 20% August 29, 30% September 1, 40% September 4, 50% September 6, 60% September 10, 70% September 12, 80% September 16, 90% September 21. Observed first fall frost in recent years: 2021 September 4, 2022 September 11, 2023 September 24, 2024 September 14, 2025 September 23.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 24Sep 6Sep 212021: September 42022: September 112023: September 242024: September 142025: September 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. ◆ 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
2021June 11September 4
2022June 15September 11
2023June 22September 24
2024June 20September 14
2025June 23September 23
2026June 12season not over yet

What these dates mean

The cautious spring date for Idaho Falls 46 W is July 1, which carries a 10 % chance of a light frost later; this low-risk point lets a gardener plan to set out tender crops after the lingering danger has largely passed.

The median spring point is the 50 % date June 11, meaning there is a 50 % chance of a light frost later than that day. In fall the cautious date is August 24, with a 10 % chance that a light frost has already arrived, offering a reliable time to finish harvesting tender crops. The median fall point is the 50 % date September 6, indicating a 50 % chance of a light frost earlier than that day. Together these dates frame the period between the two 32 °F 50 % dates, which spans 89 days.

A hard frost at 28 °F can injure plants that survive a light frost, making it a greater threat.

How to read the probabilities

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

  • Spring: "10% after July 1" 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 August 24" 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 Idaho Falls 46 W, IDNumbered nearest stations: 1 — Mackay Lost River Ranger Station, ID — 43 mi; 2 — Fort Hall, ID — 43 mi; 3 — Pocatello (Airport), ID — 46 mi; 4 — near Pocatello, ID — 52 mi; 5 — Chilly Barton Flat, ID — 54 mi.25 mi · 40 km1. Mackay Lost River Ranger Station, ID — 43 mi12. Fort Hall, ID — 43 mi23. Pocatello (Airport), ID — 46 mi34. near Pocatello, ID — 52 mi45. Chilly Barton Flat, ID — 54 mi5
  1. Mackay Lost River Ranger Station, ID 43 mi (69 km)
  2. Fort Hall, ID 43 mi (69 km)
  3. Pocatello (Airport), ID 46 mi (74 km)
  4. near Pocatello, ID 52 mi (83 km)
  5. Chilly Barton Flat, ID 54 mi (87 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 43.5317, -112.9422.