U.S. Frost Dates by Weather Station

NOAA station USC00485506 · Wyoming

Frost Dates for Leiter, WY

NOAA weather station Leiter 9 N (USC00485506), Wyoming · elevation 4160 ft (1268 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 29only 1 spring in 10 still has a frost later
  • Typical last frostMay 1450% chance of a frost after it
  • Typical first fall frostSeptember 3050% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Leiter, WYSpring: a frost after April 30 in 9 years out of 10, after May 14 in half of the years, after May 29 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before September 30 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 14First frost ~Sep 30Frost season at Leiter, WYSpring: a frost after April 30 in 9 years out of 10, after May 14 in half of the years, after May 29 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before September 30 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 137 days.JFMAMJJASONDLast frost ~May 14First frost ~Sep 30
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 29September 17
50% (typical)May 14September 30
90% (likely)April 30October 13
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 8

The last 15 years (2006–2020 normals)

Typical last frost May 12 (2 days earlier than the 30-year normal), typical first fall frost October 1 (1 day later). Frost-free season 139 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 Leiter: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 29, 20% May 25, 30% May 20, 40% May 17, 50% May 14, 60% May 11, 70% May 8, 80% May 4, 90% April 30. Observed last spring frost in recent years: 2021 May 22, 2022 May 21, 2023 April 24, 2024 June 19, 2025 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 29May 14Apr 302021: May 222022: May 212023: April 242024: June 192025: May 7Fall at Leiter: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 21, 30% September 24, 40% September 27, 50% September 30, 60% October 1, 70% October 4, 80% October 8, 90% October 13. Observed first fall frost in recent years: 2022 October 17, 2023 October 6, 2024 October 20, 2025 October 7.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Sep 30Oct 132022: October 172023: October 62024: October 202025: 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 22incomplete record
2022May 21October 17
2023April 24October 6
2024June 19October 20
2025May 7October 7
2026incomplete recordseason not over yet

What these dates mean

The cautious fall date for finishing the harvest in Leiter is September 17, when there is only a 10 % chance a light frost has arrived.

For a gardener, the 50 % light-frost dates are May 14 in spring and September 30 in fall; at each of those dates there is an even chance of a frost occurring later in spring or earlier in fall. The cautious spring date for setting out tender crops is May 29, which carries a 10 % chance of a frost later, while the cautious fall date to complete tender-crop harvest remains September 17 with the same 10 % risk of a frost earlier.

A hard frost of 28 °F matters more than a light frost of 32 °F because the lower temperature can damage plant tissue that would survive a light freeze.

How to read the probabilities

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

  • Spring: "10% after May 29" 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 17" 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 Leiter, WYNumbered nearest stations: 1 — Clearmont, WY — 20 mi; 2 — near Sheridan, WY — 34 mi; 3 — Moorhead, MT — 35 mi; 4 — Sonnette, MT — 38 mi; 5 — Buffalo, WY — 40 mi.MT25 mi · 40 km1. Clearmont, WY — 20 mi12. near Sheridan, WY — 34 mi23. Moorhead, MT — 35 mi34. Sonnette, MT — 38 mi45. Buffalo, WY — 40 mi5
  1. Clearmont, WY 20 mi (33 km)
  2. near Sheridan, WY 34 mi (54 km)
  3. Moorhead, MT 35 mi (56 km)
  4. Sonnette, MT 38 mi (60 km)
  5. Buffalo, WY 40 mi (64 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.85, -106.2889.