U.S. Frost Dates by Weather Station

NOAA station USC00101017 · Idaho

Frost Dates near Hidden Spring, ID

NOAA weather station Boise 7 N (USC00101017), Idaho · elevation 3885 ft (1184 m) · hardiness zone 7a*

Hidden Spring is the nearest town to the station (2.7 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter June 10only 1 spring in 10 still has a frost later
  • Typical last frostMay 1750% chance of a frost after it
  • Typical first fall frostOctober 1250% chance of a frost before it
  • Frost-free season147 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season near Hidden Spring, IDSpring: a frost after April 27 in 9 years out of 10, after May 17 in half of the years, after June 10 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 12 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 147 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 17First frost ~Oct 12Frost season near Hidden Spring, IDSpring: a frost after April 27 in 9 years out of 10, after May 17 in half of the years, after June 10 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 12 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 147 days.JFMAMJJASONDLast frost ~May 17First frost ~Oct 12
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 10September 27
50% (typical)May 17October 12
90% (likely)April 27October 30
Frost-free season (32°F, 50% chance)
147 days
Hard frost (28°F), last in spring, 50% chance after
April 27
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost May 13 (4 days earlier than the 30-year normal), typical first fall frost October 15 (3 days later). Frost-free season 154 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 near Hidden Spring: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 10, 20% June 3, 30% May 28, 40% May 22, 50% May 17, 60% May 13, 70% May 8, 80% May 3, 90% April 27. Observed last spring frost in recent years: 2024 May 24, 2025 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 10May 17Apr 272024: May 242025: May 20Fall near Hidden Spring: chance of a frost before this dateFall, chance of a frost before the date: 10% September 27, 20% October 1, 30% October 5, 40% October 9, 50% October 12, 60% October 15, 70% October 19, 80% October 23, 90% October 30. Observed first fall frost in recent years: 2023 October 26, 2024 October 18.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 27Oct 12Oct 302023: October 262024: October 18
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
2021incomplete recordincomplete record
2022incomplete recordincomplete record
2023incomplete recordOctober 26
2024May 24October 18
2025May 20incomplete record
2026incomplete recordseason not over yet

What these dates mean

Setting out tender crops on April 27 in the Hidden Spring area brings a 90 % chance of a light frost later, so planting that early is a gamble. The cautious spring date for tender crops is June 10, when only a 10 % chance of frost remains.

The 50 % spring date, May 17, means there is an even chance of a frost occurring after that day. In the autumn, the cautious date to finish harvesting tender crops is September 27, with just a 10 % chance a frost has already arrived, while the 50 % autumn date, October 12, marks an even chance of a frost occurring earlier. The median hard-frost dates are April 27 in spring and October 24 in fall; hard frost at 28 °F can damage plants more severely than a light frost at 32 °F because the lower temperature penetrates tissue that survives milder freezes.

How to read the probabilities

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

  • Spring: "10% after June 10" 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 27" 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 Hidden Spring, IDNumbered nearest stations: 1 — Boise (Air Terminal), ID — 12 mi; 2 — Emmett, ID — 15 mi; 3 — Garden Valley, ID — 28 mi; 4 — near Murphy, ID — 35 mi; 5 — Payette, ID — 43 mi.IDOR25 mi · 40 km1. Boise (Air Terminal), ID — 12 mi12. Emmett, ID — 15 mi23. Garden Valley, ID — 28 mi34. near Murphy, ID — 35 mi45. Payette, ID — 43 mi5
  1. Boise (Air Terminal), ID 12 mi (19 km)
  2. Emmett, ID 15 mi (25 km)
  3. Garden Valley, ID 28 mi (44 km)
  4. near Murphy, ID 35 mi (57 km)
  5. Payette, ID 43 mi (69 km)

Sources

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

Station coordinates: 43.7383, -116.2022.