U.S. Frost Dates by Weather Station

NOAA station USC00482580 · Wyoming

Frost Dates for Dillinger, WY

NOAA weather station Dillinger (USC00482580), Wyoming · elevation 4310 ft (1314 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 8only 1 spring in 10 still has a frost later
  • Typical last frostMay 2550% chance of a frost after it
  • Typical first fall frostSeptember 1750% chance of a frost before it
  • Frost-free season113 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Dillinger, WYSpring: a frost after May 13 in 9 years out of 10, after May 25 in half of the years, after June 8 in 1 year out of 10. Fall: the first frost comes before September 3 in 1 year out of 10, before September 17 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 113 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 25First frost ~Sep 17Frost season at Dillinger, WYSpring: a frost after May 13 in 9 years out of 10, after May 25 in half of the years, after June 8 in 1 year out of 10. Fall: the first frost comes before September 3 in 1 year out of 10, before September 17 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 113 days.JFMAMJJASONDLast frost ~May 25First frost ~Sep 17
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.Today

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 8September 3
50% (typical)May 25September 17
90% (likely)May 13October 1
Frost-free season (32°F, 50% chance)
113 days
Hard frost (28°F), last in spring, 50% chance after
May 13
Hard frost (28°F), first in fall, 50% chance before
September 27

The last 15 years (2006–2020 normals)

Typical last frost May 26 (1 day later than the 30-year normal), typical first fall frost September 16 (1 day earlier). Frost-free season 112 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 Dillinger: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 8, 20% June 2, 30% May 30, 40% May 27, 50% May 25, 60% May 22, 70% May 19, 80% May 16, 90% May 13. Observed last spring frost in recent years: 2021 May 29, 2022 May 24, 2023 May 8, 2024 June 19, 2025 May 22, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 8May 25May 132021: May 292022: May 242023: May 82024: June 192025: May 222026: May 20Fall at Dillinger: chance of a frost before this dateFall, chance of a frost before the date: 10% September 3, 20% September 7, 30% September 11, 40% September 14, 50% September 17, 60% September 20, 70% September 23, 80% September 26, 90% October 1. Observed first fall frost in recent years: 2021 October 12, 2022 October 23, 2023 September 29, 2025 October 12.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 3Sep 17Oct 12021: October 122022: October 232023: September 292025: October 12
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 29October 12
2022May 24October 23
2023May 8September 29
2024June 19incomplete record
2025May 22October 12
2026May 20season not over yet

What these dates mean

June 8 is the cautious spring date, giving a gardener only a 10% chance that a light frost will occur later, so tender crops can be set out with relatively low risk. The median light-frost date of May 25 marks the point where the chance of a later frost is 50%, while the median hard-frost date of May 13 marks the same odds for a temperature of 28 °F.

In the fall, September 3 is the cautious date for finishing harvest of tender crops, carrying only a 10% chance that a light frost has already arrived. The median light-frost date of September 17 and the median hard-frost date of September 27 each represent a 50% chance of a frost occurring earlier (light) or at the colder threshold (hard).

A hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F, making it a more severe threat.

How to read the probabilities

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

  • Spring: "10% after June 8" 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 3" 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 Dillinger, WYNumbered nearest stations: 1 — Upton, WY — 25 mi; 2 — Devils Tower #2, WY — 39 mi; 3 — Wright, WY — 39 mi; 4 — Dull Center, WY — 48 mi; 5 — Newcastle, WY — 49 mi.WYSD25 mi · 40 km1. Upton, WY — 25 mi12. Devils Tower #2, WY — 39 mi23. Wright, WY — 39 mi34. Dull Center, WY — 48 mi45. Newcastle, WY — 49 mi5
  1. Upton, WY 25 mi (40 km)
  2. Devils Tower #2, WY 39 mi (63 km)
  3. Wright, WY 39 mi (63 km)
  4. Dull Center, WY 48 mi (77 km)
  5. Newcastle, WY 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: 44.0992, -105.1175.