U.S. Frost Dates by Weather Station

NOAA station USC00482415 · Wyoming

Frost Dates for Deaver, WY

NOAA weather station Deaver (USC00482415), Wyoming · elevation 4105 ft (1251 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 650% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season148 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Deaver, WYSpring: a frost after April 26 in 9 years out of 10, after May 6 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 148 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 6First frost ~Oct 1Frost season at Deaver, WYSpring: a frost after April 26 in 9 years out of 10, after May 6 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 148 days.JFMAMJJASONDLast frost ~May 6First 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 20September 19
50% (typical)May 6October 1
90% (likely)April 26October 16
Frost-free season (32°F, 50% chance)
148 days
Hard frost (28°F), last in spring, 50% chance after
April 27
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 3 (3 days earlier than the 30-year normal), typical first fall frost October 5 (4 days later). Frost-free season 153 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 Deaver: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 16, 30% May 13, 40% May 9, 50% May 6, 60% May 3, 70% May 1, 80% April 29, 90% April 26. Observed last spring frost in recent years: 2021 April 25, 2022 May 22, 2023 April 29, 2024 June 19, 2025 May 7, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 6Apr 262021: April 252022: May 222023: April 292024: June 192025: May 72026: May 22Fall at Deaver: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 24, 30% September 27, 40% September 30, 50% October 1, 60% October 4, 70% October 7, 80% October 11, 90% October 16. Observed first fall frost in recent years: 2021 September 30, 2022 October 8, 2023 October 7, 2024 October 1, 2025 October 7.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 1Oct 162021: September 302022: October 82023: October 72024: October 12025: 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
2021April 25September 30
2022May 22October 8
2023April 29October 7
2024June 19October 1
2025May 7October 7
2026May 22season not over yet

What these dates mean

The 148 days between the 50% dates in Deaver, Wyoming, define the window in which most tender crops can be grown. The 50% date for spring light frost is May 6, and the 50% date for fall light frost is October 1; at each of these dates the chance of a light frost is exactly 50%.

For a cautious approach, gardeners should wait until the May 20 date in spring, which carries only a 10% chance of a light frost later, and should aim to finish tender crops by September 19 in fall, when there is only a 10% chance of a light frost earlier. The hard-frost median dates are April 27 and October 12, and a hard frost at 28 °F can damage plant tissue that often survives a light frost at 32 °F, so it represents a greater risk to tender crops.

How to read the probabilities

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

  • Spring: "10% after May 20" 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 19" 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 Deaver, WYNumbered nearest stations: 1 — Lovell, WY — 10 mi; 2 — Powell, WY — 11 mi; 3 — Emblem, WY — 29 mi; 4 — Cody, WY — 37 mi; 5 — Yellowtail Dam, MT — 43 mi.MT25 mi · 40 km1. Lovell, WY — 10 mi12. Powell, WY — 11 mi23. Emblem, WY — 29 mi34. Cody, WY — 37 mi45. Yellowtail Dam, MT — 43 mi5
  1. Lovell, WY 10 mi (16 km)
  2. Powell, WY 11 mi (18 km)
  3. Emblem, WY 29 mi (47 km)
  4. Cody, WY 37 mi (60 km)
  5. Yellowtail Dam, MT 43 mi (69 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: 44.8919, -108.5928.