U.S. Frost Dates by Weather Station

NOAA station USC00102707 · Idaho

Frost Dates for Dubois, ID

NOAA weather station Dubois Experiment Station (USC00102707), Idaho · elevation 5450 ft (1661 m) · hardiness zone 5b*

  • Lower-risk planting dateafter June 9only 1 spring in 10 still has a frost later
  • Typical last frostMay 1850% chance of a frost after it
  • Typical first fall frostSeptember 3050% chance of a frost before it
  • Frost-free season132 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Dubois, IDSpring: a frost after May 3 in 9 years out of 10, after May 18 in half of the years, after June 9 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 30 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 132 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 18First frost ~Sep 30Frost season at Dubois, IDSpring: a frost after May 3 in 9 years out of 10, after May 18 in half of the years, after June 9 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 30 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 132 days.JFMAMJJASONDLast frost ~May 18First frost ~Sep 30
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 9September 14
50% (typical)May 18September 30
90% (likely)May 3October 16
Frost-free season (32°F, 50% chance)
132 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 18 (same as the 30-year normal), typical first fall frost October 1 (1 day later). Frost-free season 134 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 Dubois: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 9, 20% June 1, 30% May 27, 40% May 22, 50% May 18, 60% May 14, 70% May 11, 80% May 8, 90% May 3. Observed last spring frost in recent years: 2021 June 11, 2022 May 21, 2023 May 8, 2024 June 18, 2025 April 22, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 9May 18May 32021: June 112022: May 212023: May 82024: June 182025: April 222026: May 22Fall at Dubois: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 19, 30% September 24, 40% September 27, 50% September 30, 60% October 3, 70% October 6, 80% October 10, 90% October 16. Observed first fall frost in recent years: 2021 September 20, 2022 October 14, 2023 October 26, 2024 October 19, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Nov 1Sep 14Sep 30Oct 162021: September 202022: October 142023: October 262024: October 192025: October 6
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 20
2022May 21October 14
2023May 8October 26
2024June 18October 19
2025April 22October 6
2026May 22season not over yet

What these dates mean

Planting tender crops on the early spring date of May 3 in Dubois carries a 90% chance that a light frost (32 °F) will still occur later, so gardeners treat it as a gamble.

The median point for light frost in spring in Dubois is the 50% date of May 18, meaning an equal chance of frost occurring on either side of that day; the cautious spring date is June 9, which has only a 10% chance of a later frost. In autumn the median light-frost point is the 50% date of September 30, and the cautious fall date is September 14, with only a 10% chance that frost has arrived earlier.

Hard-frost thresholds at 28 °F, marked by the 50% dates of May 2 and October 12, are more damaging than the 32 °F light-frost thresholds because they can freeze plant tissue more deeply.

How to read the probabilities

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

  • Spring: "10% after June 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 September 14" 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 Dubois, IDNumbered nearest stations: 1 — Idaho Falls 46 W, ID — 62 mi; 2 — Alta, WY — 66 mi; 3 — near Dillon, MT — 70 mi; 4 — Dillon (Airport), MT — 72 mi; 5 — Mackay Lost River Ranger Station, ID — 74 mi.IDMTWY50 mi · 80 km1. Idaho Falls 46 W, ID — 62 mi12. Alta, WY — 66 mi23. near Dillon, MT — 70 mi34. Dillon (Airport), MT — 72 mi45. Mackay Lost River Ranger Station, ID — 74 mi5
  1. Idaho Falls 46 W, ID 62 mi (99 km)
  2. Alta, WY 66 mi (107 km)
  3. near Dillon, MT 70 mi (113 km)
  4. Dillon (Airport), MT 72 mi (116 km)
  5. Mackay Lost River Ranger Station, ID 74 mi (119 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.2436, -112.2006.