U.S. Frost Dates by Weather Station

NOAA station USC00107346 · Idaho

Frost Dates for Preston, ID

NOAA weather station Preston (USC00107346), Idaho · elevation 4719 ft (1438 m) · hardiness zone 6a*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 1650% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season133 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Preston, IDSpring: a frost after May 2 in 9 years out of 10, after May 16 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 133 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 16First frost ~Sep 28Frost season at Preston, IDSpring: a frost after May 2 in 9 years out of 10, after May 16 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 133 days.JFMAMJJASONDLast frost ~May 16First frost ~Sep 28
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 4September 14
50% (typical)May 16September 28
90% (likely)May 2October 14
Frost-free season (32°F, 50% chance)
133 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 16 (same as the 30-year normal), typical first fall frost October 1 (3 days later). Frost-free season 135 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 Preston: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 28, 30% May 24, 40% May 20, 50% May 16, 60% May 13, 70% May 9, 80% May 6, 90% May 2. Observed last spring frost in recent years: 2021 May 12, 2022 June 15, 2023 April 26, 2024 June 18, 2025 May 19, 2026 June 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 16May 22021: May 122022: June 152023: April 262024: June 182025: May 192026: June 11Fall at Preston: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 19, 30% September 23, 40% September 26, 50% September 28, 60% October 1, 70% October 4, 80% October 7, 90% October 14. Observed first fall frost in recent years: 2021 September 21, 2022 October 20, 2023 October 26, 2024 October 19, 2025 October 7.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Nov 1Sep 14Sep 28Oct 142021: September 212022: October 202023: October 262024: October 192025: October 7
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 21
2022June 15October 20
2023April 26October 26
2024June 18October 19
2025May 19October 7
2026June 11season not over yet

What these dates mean

September 14 is the cautious fall date for tender crops in Preston; only a 10 % chance exists that a light frost has arrived before that day, making it the preferred deadline to finish harvesting. In spring the cautious date is June 4, when there is only a 10 % chance of a light frost occurring after that date, so tender seedlings are safest to set out on or after it.

The 50 % dates represent the point at which a light frost is equally likely to have happened or not. May 16 marks that median in spring and September 28 does so in fall. Hard-frost conditions (28 °F) are tracked separately, with the median dates April 30 and October 10; a hard frost can damage plants that survive a light frost, so it is a more critical 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 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 14" 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 Preston, IDNumbered nearest stations: 1 — Richmond, UT — 13 mi; 2 — near Garland, UT — 20 mi; 3 — near Logan, UT — 24 mi; 4 — Logan Radio Kvnu, UT — 25 mi; 5 — near Paris, ID — 29 mi.IDWY25 mi · 40 km1. Richmond, UT — 13 mi12. near Garland, UT — 20 mi23. near Logan, UT — 24 mi34. Logan Radio Kvnu, UT — 25 mi45. near Paris, ID — 29 mi5
  1. Richmond, UT 13 mi (22 km)
  2. near Garland, UT 20 mi (32 km)
  3. near Logan, UT 24 mi (39 km)
  4. Logan Radio Kvnu, UT 25 mi (40 km)
  5. near Paris, ID 29 mi (47 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: 42.0933, -111.8825.