U.S. Frost Dates by Weather Station

NOAA station USC00489770 · Wyoming

Frost Dates for Worland (USC00489770), WY

NOAA weather station Worland (USC00489770), Wyoming · elevation 4058 ft (1237 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 18only 1 spring in 10 still has a frost later
  • Typical last frostMay 450% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season149 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Worland (USC00489770), WYSpring: a frost after April 23 in 9 years out of 10, after May 4 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 149 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 4First frost ~Oct 1Frost season at Worland (USC00489770), WYSpring: a frost after April 23 in 9 years out of 10, after May 4 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 149 days.JFMAMJJASONDLast frost ~May 4First frost ~Oct 1
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 18September 21
50% (typical)May 4October 1
90% (likely)April 23October 15
Frost-free season (32°F, 50% chance)
149 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 13

The last 15 years (2006–2020 normals)

Typical last frost May 3 (1 day earlier than the 30-year normal), typical first fall frost October 4 (3 days later). Frost-free season 152 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 (USC00489770): chance of a frost after this dateSpring, chance of a frost after the date: 10% May 18, 20% May 14, 30% May 10, 40% May 7, 50% May 4, 60% May 2, 70% April 30, 80% April 27, 90% April 23. Observed last spring frost in recent years: 2021 May 10, 2022 May 23, 2023 April 29, 2024 May 4, 2025 April 24, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 18May 4Apr 232021: May 102022: May 232023: April 292024: May 42025: April 242026: May 20Fall at Worland (USC00489770): chance of a frost before this dateFall, chance of a frost before the date: 10% September 21, 20% September 25, 30% September 28, 40% September 30, 50% October 1, 60% October 4, 70% October 6, 80% October 10, 90% October 15. Observed first fall frost in recent years: 2021 September 30, 2022 October 15, 2023 October 26, 2024 October 2, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 21Oct 1Oct 152021: September 302022: October 152023: October 262024: October 22025: October 8
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 10September 30
2022May 23October 15
2023April 29October 26
2024May 4October 2
2025April 24October 8
2026May 20season not over yet

What these dates mean

May 18 is the cautious spring light-frost date, with only a 10 % chance of a frost later than that day, and it lets a gardener plan the first planting of tender crops. The 50 % light-frost date is May 4; at that point there is an even chance of a frost occurring later in the season, though the day itself is not a frost date. The median hard-frost date for spring is April 24, marking the point at which a 28 °F freeze becomes a 50 % likelihood.

September 21 is the cautious fall light-frost date, carrying a 10 % chance that a frost has arrived earlier, and it indicates the latest time to finish harvesting tender crops. The 50 % light-frost date for fall is October 1, and the median hard-frost date for fall is October 13. A hard frost at 28 °F matters more than a light frost because the lower temperature can damage plants that would otherwise survive a 32 °F event.

How to read the probabilities

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

  • Spring: "10% after May 18" 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 21" 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 (USC00489770), WYNumbered nearest stations: 1 — Worland (USW00024062), WY — 3 mi; 2 — Basin, WY — 26 mi; 3 — Thermopolis, WY — 28 mi; 4 — Tensleep 4 NE, WY — 29 mi; 5 — Tensleep 16 SSE, WY — 33 mi.25 mi · 40 km1. Worland (USW00024062), WY — 3 mi12. Basin, WY — 26 mi23. Thermopolis, WY — 28 mi34. Tensleep 4 NE, WY — 29 mi45. Tensleep 16 SSE, WY — 33 mi5
  1. Worland (USW00024062), WY 3 mi (5 km)
  2. Basin, WY 26 mi (41 km)
  3. Thermopolis, WY 28 mi (45 km)
  4. Tensleep 4 NE, WY 29 mi (47 km)
  5. Tensleep 16 SSE, WY 33 mi (53 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: 44.0114, -107.9683.