U.S. Frost Dates by Weather Station

NOAA station USC00482466 · Wyoming

Frost Dates for Devils Tower #2, WY

NOAA weather station Devils Tower #2 (USC00482466), Wyoming · elevation 3862 ft (1177 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 6only 1 spring in 10 still has a frost later
  • Typical last frostMay 2350% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season118 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Devils Tower #2, WYSpring: a frost after May 12 in 9 years out of 10, after May 23 in half of the years, after June 6 in 1 year out of 10. Fall: the first frost comes before September 4 in 1 year out of 10, before September 20 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 118 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 23First frost ~Sep 20Frost season at Devils Tower #2, WYSpring: a frost after May 12 in 9 years out of 10, after May 23 in half of the years, after June 6 in 1 year out of 10. Fall: the first frost comes before September 4 in 1 year out of 10, before September 20 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 118 days.JFMAMJJASONDLast frost ~May 23First 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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 6September 4
50% (typical)May 23September 20
90% (likely)May 12October 4
Frost-free season (32°F, 50% chance)
118 days
Hard frost (28°F), last in spring, 50% chance after
May 12
Hard frost (28°F), first in fall, 50% chance before
October 1

The last 15 years (2006–2020 normals)

Typical last frost May 24 (1 day later than the 30-year normal), typical first fall frost September 22 (2 days later). Frost-free season 116 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 Devils Tower #2: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 6, 20% May 31, 30% May 28, 40% May 26, 50% May 23, 60% May 21, 70% May 19, 80% May 16, 90% May 12. Observed last spring frost in recent years: 2021 May 13, 2022 June 2, 2024 June 19, 2025 May 22, 2026 May 23.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 6May 23May 122021: May 132022: June 22024: June 192025: May 222026: May 23Fall at Devils Tower #2: chance of a frost before this dateFall, chance of a frost before the date: 10% September 4, 20% September 9, 30% September 14, 40% September 17, 50% September 20, 60% September 23, 70% September 27, 80% September 30, 90% October 4. Observed first fall frost in recent years: 2021 September 17, 2022 October 8, 2024 September 22, 2025 September 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 4Sep 20Oct 42021: September 172022: October 82024: September 222025: September 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. ◆ 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 13September 17
2022June 2October 8
2023incomplete recordincomplete record
2024June 19September 22
2025May 22September 5
2026May 23season not over yet

What these dates mean

June 6 is the cautious spring date at Devils Tower #2, allowing a gardener to plan setting out tender crops with only a small risk of a light frost. The counterpart cautious fall date is September 4, giving a gardener a narrow window to finish harvesting tender crops before a light frost becomes likely.

The 50% date is May 23, meaning there is a 50% chance of a light frost later than this date, while the 50% date is September 20, meaning there is a 50% chance of a light frost earlier than this date. Hard-frost risk is indicated by the 28 °F median dates: May 12 in spring and October 1 in fall; a hard frost at 28 °F can damage plants that survive a 32 °F 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 6" 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 4" 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 Devils Tower #2, WYNumbered nearest stations: 1 — Upton, WY — 34 mi; 2 — Dillinger, WY — 39 mi; 3 — Spearfish, SD — 42 mi; 4 — Belle Fourche, SD — 43 mi; 5 — Biddle, MT — 49 mi.WYSDMT25 mi · 40 km1. Upton, WY — 34 mi12. Dillinger, WY — 39 mi23. Spearfish, SD — 42 mi34. Belle Fourche, SD — 43 mi45. Biddle, MT — 49 mi5
  1. Upton, WY 34 mi (55 km)
  2. Dillinger, WY 39 mi (63 km)
  3. Spearfish, SD 42 mi (67 km)
  4. Belle Fourche, SD 43 mi (69 km)
  5. Biddle, MT 49 mi (79 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: 44.5833, -104.7147.