U.S. Frost Dates by Weather Station

NOAA station USC00103448 · Idaho

Frost Dates for Garden Valley, ID

NOAA weather station Garden Valley (USC00103448), Idaho · elevation 3100 ft (945 m) · hardiness zone 6b*

  • Lower-risk planting dateafter June 20only 1 spring in 10 still has a frost later
  • Typical last frostJune 150% chance of a frost after it
  • Typical first fall frostSeptember 1050% chance of a frost before it
  • Frost-free season102 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Garden Valley, IDSpring: a frost after May 13 in 9 years out of 10, after June 1 in half of the years, after June 20 in 1 year out of 10. Fall: the first frost comes before August 28 in 1 year out of 10, before September 10 in half of the years, before September 27 in 9 years out of 10. Typical frost-free season: 102 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 1First frost ~Sep 10Frost season at Garden Valley, IDSpring: a frost after May 13 in 9 years out of 10, after June 1 in half of the years, after June 20 in 1 year out of 10. Fall: the first frost comes before August 28 in 1 year out of 10, before September 10 in half of the years, before September 27 in 9 years out of 10. Typical frost-free season: 102 days.JFMAMJJASONDLast frost ~Jun 1First frost ~Sep 10
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 20August 28
50% (typical)June 1September 10
90% (likely)May 13September 27
Frost-free season (32°F, 50% chance)
102 days
Hard frost (28°F), last in spring, 50% chance after
May 11
Hard frost (28°F), first in fall, 50% chance before
September 24

The last 15 years (2006–2020 normals)

Typical last frost May 31 (1 day earlier than the 30-year normal), typical first fall frost September 11 (1 day later). Frost-free season 106 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 Garden Valley: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 20, 20% June 14, 30% June 10, 40% June 6, 50% June 1, 60% May 27, 70% May 23, 80% May 18, 90% May 13.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1Jun 20Jun 1May 13Fall at Garden Valley: chance of a frost before this dateFall, chance of a frost before the date: 10% August 28, 20% September 1, 30% September 4, 40% September 6, 50% September 10, 60% September 13, 70% September 17, 80% September 20, 90% September 27.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 28Sep 10Sep 27
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.

What these dates mean

The 102 days between the 50% dates of June 1 and September 10 in Garden Valley mark the window when a light frost is no more likely than not; gardeners can treat this span as the period of even odds for a 32 °F frost. The median dates themselves are not frost dates but simply the points at which the historical record shows a fifty-fifty chance for a light frost.

To reduce risk for tender crops, the cautious spring date is June 20, which carries only a ten-percent chance of a light frost occurring later, while the early-season gamble date is May 13 with a ninety-percent chance of frost later. In the fall the cautious date is August 28, with only a ten-percent chance of a light frost arriving earlier, and the late-season gamble date is September 27 with a ninety-percent chance of frost earlier.

A hard frost at 28 °F—recorded with fifty-percent dates of May 11 and September 24—can damage plants 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 20" 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 28" 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 Garden Valley, IDNumbered nearest stations: 1 — near Hidden Spring, ID — 28 mi; 2 — Emmett, ID — 30 mi; 3 — Boise (Air Terminal), ID — 39 mi; 4 — Payette, ID — 48 mi; 5 — Cambridge, ID — 48 mi.OR25 mi · 40 km1. near Hidden Spring, ID — 28 mi12. Emmett, ID — 30 mi23. Boise (Air Terminal), ID — 39 mi34. Payette, ID — 48 mi45. Cambridge, ID — 48 mi5
  1. near Hidden Spring, ID 28 mi (44 km)
  2. Emmett, ID 30 mi (48 km)
  3. Boise (Air Terminal), ID 39 mi (63 km)
  4. Payette, ID 48 mi (77 km)
  5. Cambridge, ID 48 mi (77 km)

Sources

* Hardiness zone 6b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.1011, -115.9694.