U.S. Frost Dates by Weather Station

NOAA station USW00024029 · Wyoming

Frost Dates near Sheridan, WY

NOAA weather station Sheridan County Airport (USW00024029), Wyoming · elevation 3945 ft (1202 m) · hardiness zone 5a*

Sheridan is the nearest town to the station (2.0 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter June 6only 1 spring in 10 still has a frost later
  • Typical last frostMay 2150% chance of a frost after it
  • Typical first fall frostSeptember 2350% chance of a frost before it
  • Frost-free season123 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season near Sheridan, WYSpring: a frost after May 7 in 9 years out of 10, after May 21 in half of the years, after June 6 in 1 year out of 10. Fall: the first frost comes before September 9 in 1 year out of 10, before September 23 in half of the years, before October 6 in 9 years out of 10. Typical frost-free season: 123 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 21First frost ~Sep 23Frost season near Sheridan, WYSpring: a frost after May 7 in 9 years out of 10, after May 21 in half of the years, after June 6 in 1 year out of 10. Fall: the first frost comes before September 9 in 1 year out of 10, before September 23 in half of the years, before October 6 in 9 years out of 10. Typical frost-free season: 123 days.JFMAMJJASONDLast frost ~May 21First frost ~Sep 23
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 6September 9
50% (typical)May 21September 23
90% (likely)May 7October 6
Frost-free season (32°F, 50% chance)
123 days
Hard frost (28°F), last in spring, 50% chance after
May 7
Hard frost (28°F), first in fall, 50% chance before
October 3

The last 15 years (2006–2020 normals)

Typical last frost May 19 (2 days earlier than the 30-year normal), typical first fall frost September 25 (2 days later). Frost-free season 126 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 near Sheridan: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 6, 20% May 31, 30% May 27, 40% May 24, 50% May 21, 60% May 18, 70% May 15, 80% May 12, 90% May 7. Observed last spring frost in recent years: 2021 May 11, 2022 June 1, 2023 April 30, 2024 June 19, 2025 May 22, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 6May 21May 72021: May 112022: June 12023: April 302024: June 192025: May 222026: May 20Fall near Sheridan: chance of a frost before this dateFall, chance of a frost before the date: 10% September 9, 20% September 16, 30% September 18, 40% September 21, 50% September 23, 60% September 26, 70% September 28, 80% October 1, 90% October 6. Observed first fall frost in recent years: 2021 September 30, 2022 October 9, 2023 October 13, 2024 October 1, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 9Sep 23Oct 62021: September 302022: October 92023: October 132024: October 12025: September 6
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 11September 30
2022June 1October 9
2023April 30October 13
2024June 19October 1
2025May 22September 6
2026May 20season not over yet

What these dates mean

The 123 days between the 50% dates in the Sheridan area frame the period when tender crops can be grown with balanced risk. The 50% spring date is May 21, indicating a 50 % chance of a light frost later, while the 50% fall date is September 23, marking a 50 % chance of a light frost earlier. Gardeners can view this interval as the window where the odds of a damaging 32 °F frost are roughly even on either side.

Because the cautious spring date is June 6 (10 % chance of a later frost), planting tender crops after that date follows the low-risk plan; the cautious fall date is September 9 (10 % chance of an earlier frost), so finishing harvest before then keeps risk low. Setting out seedlings on May 7 or keeping them until October 6 would be a gamble with a 90 % chance of frost. A hard frost at 28 °F is more severe than a light frost at 32 °F because it can damage plant tissue that survives a milder freeze.

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 9" 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 Sheridan, WYNumbered nearest stations: 1 — Clearmont, WY — 29 mi; 2 — Buffalo, WY — 32 mi; 3 — Leiter, WY — 34 mi; 4 — Tensleep 4 NE, WY — 53 mi; 5 — Busby, MT — 53 mi.MT50 mi · 80 km1. Clearmont, WY — 29 mi12. Buffalo, WY — 32 mi23. Leiter, WY — 34 mi34. Tensleep 4 NE, WY — 53 mi45. Busby, MT — 53 mi5
  1. Clearmont, WY 29 mi (46 km)
  2. Buffalo, WY 32 mi (51 km)
  3. Leiter, WY 34 mi (54 km)
  4. Tensleep 4 NE, WY 53 mi (85 km)
  5. Busby, MT 53 mi (86 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: 44.7694, -106.9689.