U.S. Frost Dates by Weather Station

NOAA station USC00107673 · Idaho

Frost Dates for Richfield, ID

NOAA weather station Richfield (USC00107673), Idaho · elevation 4309 ft (1313 m) · hardiness zone 6a*

  • Lower-risk planting dateafter June 14only 1 spring in 10 still has a frost later
  • Typical last frostMay 2450% chance of a frost after it
  • Typical first fall frostSeptember 2650% chance of a frost before it
  • Frost-free season123 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Richfield, IDSpring: a frost after May 6 in 9 years out of 10, after May 24 in half of the years, after June 14 in 1 year out of 10. Fall: the first frost comes before September 10 in 1 year out of 10, before September 26 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 123 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 24First frost ~Sep 26Frost season at Richfield, IDSpring: a frost after May 6 in 9 years out of 10, after May 24 in half of the years, after June 14 in 1 year out of 10. Fall: the first frost comes before September 10 in 1 year out of 10, before September 26 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 123 days.JFMAMJJASONDLast frost ~May 24First frost ~Sep 26
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)June 14September 10
50% (typical)May 24September 26
90% (likely)May 6October 10
Frost-free season (32°F, 50% chance)
123 days
Hard frost (28°F), last in spring, 50% chance after
May 8
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 21 (3 days earlier than the 30-year normal), typical first fall frost September 28 (2 days later). Frost-free season 127 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 Richfield: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 14, 20% June 7, 30% June 1, 40% May 28, 50% May 24, 60% May 20, 70% May 16, 80% May 13, 90% May 6. Observed last spring frost in recent years: 2021 May 12, 2022 June 16, 2023 May 8, 2024 June 18, 2025 April 22, 2026 May 18.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 14May 24May 62021: May 122022: June 162023: May 82024: June 182025: April 222026: May 18Fall at Richfield: chance of a frost before this dateFall, chance of a frost before the date: 10% September 10, 20% September 16, 30% September 20, 40% September 23, 50% September 26, 60% September 29, 70% October 1, 80% October 5, 90% October 10. Observed first fall frost in recent years: 2021 September 29, 2022 October 19, 2023 October 26, 2024 October 3, 2025 October 12.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Nov 1Sep 10Sep 26Oct 102021: September 292022: October 192023: October 262024: October 32025: October 12
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 12September 29
2022June 16October 19
2023May 8October 26
2024June 18October 3
2025April 22October 12
2026May 18season not over yet

What these dates mean

Setting out tender crops on May 6 in Richfield is a gamble, because there is a 90 % chance of a light frost later than that date.

The 50% date is May 24; it marks the point at which a light frost is equally likely to occur later or not, giving gardeners a statistical midpoint for planning. For a cautious approach, the spring date to aim for is June 14, which carries only a 10 % chance of a frost later, while the fall cautious date is September 10, with a 10 % chance of a frost earlier. The 50% date is September 26, offering the same even odds in autumn.

The 50% hard-frost dates are May 8 and October 7, and a hard frost at 28 °F can damage plant tissue that survives 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 14" 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 10" 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 Richfield, IDNumbered nearest stations: 1 — Shoshone, ID — 15 mi; 2 — Hazelton, ID — 31 mi; 3 — Paul, ID — 36 mi; 4 — Burley, ID — 40 mi; 5 — Minidoka Dam, ID — 42 mi.ID25 mi · 40 km1. Shoshone, ID — 15 mi12. Hazelton, ID — 31 mi23. Paul, ID — 36 mi34. Burley, ID — 40 mi45. Minidoka Dam, ID — 42 mi5
  1. Shoshone, ID 15 mi (25 km)
  2. Hazelton, ID 31 mi (51 km)
  3. Paul, ID 36 mi (58 km)
  4. Burley, ID 40 mi (65 km)
  5. Minidoka Dam, ID 42 mi (68 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: 43.0517, -114.155.