U.S. Frost Dates by Weather Station

NOAA station USW00024062 · Wyoming

Frost Dates for Worland (USW00024062), WY

NOAA weather station Worland (USW00024062), Wyoming · elevation 4172 ft (1272 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 27only 1 spring in 10 still has a frost later
  • Typical last frostMay 1350% chance of a frost after it
  • Typical first fall frostSeptember 2650% chance of a frost before it
  • Frost-free season133 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Worland (USW00024062), WYSpring: a frost after May 2 in 9 years out of 10, after May 13 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 26 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 133 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 13First frost ~Sep 26Frost season at Worland (USW00024062), WYSpring: a frost after May 2 in 9 years out of 10, after May 13 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 26 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 133 days.JFMAMJJASONDLast frost ~May 13First frost ~Sep 26
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 27September 14
50% (typical)May 13September 26
90% (likely)May 2October 7
Frost-free season (32°F, 50% chance)
133 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 11 (2 days earlier than the 30-year normal), typical first fall frost September 28 (2 days later). Frost-free season 136 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 Worland (USW00024062): chance of a frost after this dateSpring, chance of a frost after the date: 10% May 27, 20% May 22, 30% May 18, 40% May 15, 50% May 13, 60% May 10, 70% May 8, 80% May 5, 90% May 2. Observed last spring frost in recent years: 2021 May 11, 2022 June 15, 2023 April 29, 2024 June 19, 2025 May 3, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 27May 13May 22021: May 112022: June 152023: April 292024: June 192025: May 32026: May 22Fall at Worland (USW00024062): chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 18, 30% September 21, 40% September 24, 50% September 26, 60% September 28, 70% October 1, 80% October 3, 90% October 7. Observed first fall frost in recent years: 2021 September 21, 2022 October 8, 2023 October 7, 2024 September 22, 2025 October 7.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 26Oct 72021: September 212022: October 82023: October 72024: September 222025: 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 11September 21
2022June 15October 8
2023April 29October 7
2024June 19September 22
2025May 3October 7
2026May 22season not over yet

What these dates mean

September 14 marks the cautious fall date for finishing the harvest of tender crops in Worland; only a 10% chance of a light frost has occurred earlier.

For a gardener the 50% dates—May 13 for spring and September 26 for fall—indicate the point at which a light frost is equally likely to be earlier or later, but they are not frost dates themselves. The cautious spring date for setting out tender crops is May 27, when the chance of a later light frost has dropped to 10%; planting on May 2 carries a 90% chance of a frost and is a gamble.

A hard frost at 28°F can damage plants more severely than a light frost at 32°F, so it is a more critical threshold for winter survival.

How to read the probabilities

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

  • Spring: "10% after May 27" 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 Worland (USW00024062), WYNumbered nearest stations: 1 — Worland (USC00489770), WY — 3 mi; 2 — Thermopolis, WY — 25 mi; 3 — Basin, WY — 29 mi; 4 — Tensleep 4 NE, WY — 29 mi; 5 — Tensleep 16 SSE, WY — 31 mi.25 mi · 40 km1. Worland (USC00489770), WY — 3 mi12. Thermopolis, WY — 25 mi23. Basin, WY — 29 mi34. Tensleep 4 NE, WY — 29 mi45. Tensleep 16 SSE, WY — 31 mi5
  1. Worland (USC00489770), WY 3 mi (5 km)
  2. Thermopolis, WY 25 mi (41 km)
  3. Basin, WY 29 mi (47 km)
  4. Tensleep 4 NE, WY 29 mi (47 km)
  5. Tensleep 16 SSE, WY 31 mi (50 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 43.9658, -107.9508.