U.S. Frost Dates by Weather Station

NOAA station USC00106424 · Idaho

Frost Dates for Nezperce, ID

NOAA weather station Nezperce (USC00106424), Idaho · elevation 3248 ft (990 m) · hardiness zone 6b*

  • Lower-risk planting dateafter June 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 2450% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season116 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Nezperce, IDSpring: a frost after May 6 in 9 years out of 10, after May 24 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before September 1 in 1 year out of 10, before September 20 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 116 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 24First frost ~Sep 20Frost season at Nezperce, IDSpring: a frost after May 6 in 9 years out of 10, after May 24 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before September 1 in 1 year out of 10, before September 20 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 116 days.JFMAMJJASONDLast frost ~May 24First frost ~Sep 20
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 19September 1
50% (typical)May 24September 20
90% (likely)May 6October 5
Frost-free season (32°F, 50% chance)
116 days
Hard frost (28°F), last in spring, 50% chance after
May 5
Hard frost (28°F), first in fall, 50% chance before
October 2

The last 15 years (2006–2020 normals)

Typical last frost May 24 (same as the 30-year normal), typical first fall frost September 20. Frost-free season 118 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 Nezperce: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 19, 20% June 10, 30% June 3, 40% May 29, 50% May 24, 60% May 20, 70% May 16, 80% May 12, 90% May 6.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1Jun 19May 24May 6Fall at Nezperce: chance of a frost before this dateFall, chance of a frost before the date: 10% September 1, 20% September 7, 30% September 12, 40% September 16, 50% September 20, 60% September 23, 70% September 26, 80% September 30, 90% October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 1Sep 20Oct 5
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 116 days between the 50% dates in Nezperce—May 24 in spring and September 20 in fall—frame the period when light frosts are equally likely to have occurred or not. For a gardener this midpoint marks the central point of the frost probability curve, with a 50 % chance of a 32 °F frost later than May 24 and a 50 % chance of a frost earlier than September 20.

The cautious spring date for setting out tender crops is June 19, which carries only a 10 % chance of a frost later; planting on May 6 carries a 90 % chance and is a gamble. In fall the cautious date to finish harvesting tender crops is September 1, with a 10 % chance of a frost earlier, while waiting until October 5 involves a 90 % chance. The hard-frost 28 °F median dates are May 5 and October 2, and a hard frost can damage plants that survive a light frost, making it the more critical temperature threshold.

How to read the probabilities

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

  • Spring: "10% after June 19" 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 1" 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 Nezperce, IDNumbered nearest stations: 1 — Cottonwood, ID — 15 mi; 2 — near Orofino, ID — 19 mi; 3 — near Lewiston, ID — 38 mi; 4 — Pullman, WA — 58 mi; 5 — Saint Maries, ID — 77 mi.IDWAMT25 mi · 40 km1. Cottonwood, ID — 15 mi12. near Orofino, ID — 19 mi23. near Lewiston, ID — 38 mi34. Pullman, WA — 58 mi45. Saint Maries, ID — 77 mi5
  1. Cottonwood, ID 15 mi (25 km)
  2. near Orofino, ID 19 mi (31 km)
  3. near Lewiston, ID 38 mi (61 km)
  4. Pullman, WA 58 mi (93 km)
  5. Saint Maries, ID 77 mi (123 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: 46.2325, -116.243.