U.S. Frost Dates by Weather Station

NOAA station USC00101408 · Idaho

Frost Dates for Cambridge, ID

NOAA weather station Cambridge (USC00101408), Idaho · elevation 2650 ft (808 m) · hardiness zone 6a*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season134 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Cambridge, IDSpring: a frost after April 29 in 9 years out of 10, after May 15 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 27 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 134 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 27Frost season at Cambridge, IDSpring: a frost after April 29 in 9 years out of 10, after May 15 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 27 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 134 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 27
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)June 4September 12
50% (typical)May 15September 27
90% (likely)April 29October 9
Frost-free season (32°F, 50% chance)
134 days
Hard frost (28°F), last in spring, 50% chance after
April 28
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 16 (1 day later than the 30-year normal), typical first fall frost September 28 (1 day later). Frost-free season 132 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 Cambridge: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 29, 30% May 22, 40% May 17, 50% May 15, 60% May 11, 70% May 8, 80% May 3, 90% April 29. Observed last spring frost in recent years: 2021 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 15Apr 292021: May 11Fall at Cambridge: chance of a frost before this dateFall, chance of a frost before the date: 10% September 12, 20% September 17, 30% September 21, 40% September 24, 50% September 27, 60% September 30, 70% October 2, 80% October 5, 90% October 9. Observed first fall frost in recent years: 2021 September 17.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 12Sep 27Oct 92021: September 17
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 11September 17
2022no datano data
2023no datano data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

Setting out tender crops on April 29 in Cambridge is a gamble, because there is a 90 % chance of a light frost later than that date. The risk-averse gardener would wait until June 4, when only a 10 % chance remains for a frost after planting. For a light-frost perspective, the 50 % date of May 15 marks the point at which the odds are even for a frost to occur later in spring.

In the autumn, September 12 serves as the cautious date for finishing tender-crop harvests, with just a 10 % chance that a frost has arrived earlier. Waiting until October 9 would be a gamble, as a frost is 90 % likely before that date. The 50 % date of September 27 indicates equal odds for a frost earlier in the season. Hard-frost dates—April 28 in spring and October 7 in fall—signal when temperatures reaching 28 °F become a concern, because a hard frost can damage plant tissue more severely than 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 4" 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 12" 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 Cambridge, IDNumbered nearest stations: 1 — Halfway, OR — 30 mi; 2 — McCall, ID — 35 mi; 3 — Payette, ID — 37 mi; 4 — Garden Valley, ID — 48 mi; 5 — Emmett, ID — 51 mi.IDOR25 mi · 40 km1. Halfway, OR — 30 mi12. McCall, ID — 35 mi23. Payette, ID — 37 mi34. Garden Valley, ID — 48 mi45. Emmett, ID — 51 mi5
  1. Halfway, OR 30 mi (48 km)
  2. McCall, ID 35 mi (57 km)
  3. Payette, ID 37 mi (59 km)
  4. Garden Valley, ID 48 mi (77 km)
  5. Emmett, ID 51 mi (82 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: 44.5733, -116.6753.