U.S. Frost Dates by Weather Station

NOAA station USC00483031 · Wyoming

Frost Dates for Emblem, WY

NOAA weather station Emblem (USC00483031), Wyoming · elevation 4448 ft (1356 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 27only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season136 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Emblem, WYSpring: a frost after April 30 in 9 years out of 10, after May 12 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 28 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 136 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Sep 28Frost season at Emblem, WYSpring: a frost after April 30 in 9 years out of 10, after May 12 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 28 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 136 days.JFMAMJJASONDLast frost ~May 12First frost ~Sep 28
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 12September 28
90% (likely)April 30October 10
Frost-free season (32°F, 50% chance)
136 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 11 (1 day earlier than the 30-year normal), typical first fall frost October 1 (3 days later). Frost-free season 141 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 Emblem: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 27, 20% May 21, 30% May 18, 40% May 15, 50% May 12, 60% May 9, 70% May 7, 80% May 3, 90% April 30. Observed last spring frost in recent years: 2021 May 21, 2022 May 23, 2023 April 26, 2024 May 24.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 27May 12Apr 302021: May 212022: May 232023: April 262024: May 24Fall at Emblem: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 18, 30% September 22, 40% September 25, 50% September 28, 60% September 30, 70% October 2, 80% October 5, 90% October 10. Observed first fall frost in recent years: 2021 September 29, 2023 October 7, 2024 October 1.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 28Oct 102021: September 292023: October 72024: October 1
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 21September 29
2022May 23incomplete record
2023April 26October 7
2024May 24October 1
2025no datano data
2026no dataseason not over yet

What these dates mean

The 136 days between the 32 °F 50% dates in Emblem, Wyoming, frame the interval where the chance of a light frost is below 50 % on either side. The median light-frost dates are May 12 in spring and September 28 in fall; the chance of a frost later in the season rises sharply when dates precede May 12, and the chance of a frost earlier in the season rises sharply when dates follow September 28.

For a cautious plan, tender crops should be set out no earlier than May 27, which carries only a 10 % chance of a later frost, and should be finished by September 14, which carries only a 10 % chance that a frost has already arrived. The hard-frost 50% dates are May 1 and October 7, and a hard frost at 28 °F can damage plant tissue that a light frost at 32 °F typically does not.

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 Emblem, WYNumbered nearest stations: 1 — Basin, WY — 19 mi; 2 — Lovell, WY — 24 mi; 3 — Powell, WY — 26 mi; 4 — Deaver, WY — 29 mi; 5 — Cody, WY — 36 mi.WYMT25 mi · 40 km1. Basin, WY — 19 mi12. Lovell, WY — 24 mi23. Powell, WY — 26 mi34. Deaver, WY — 29 mi45. Cody, WY — 36 mi5
  1. Basin, WY 19 mi (31 km)
  2. Lovell, WY 24 mi (38 km)
  3. Powell, WY 26 mi (43 km)
  4. Deaver, WY 29 mi (47 km)
  5. Cody, WY 36 mi (57 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.4972, -108.3906.