U.S. Frost Dates by Weather Station

NOAA station USC00486852 · Wyoming

Frost Dates for Old Fort Laramie, WY

NOAA weather station Old Fort Laramie (USC00486852), Wyoming · elevation 4250 ft (1295 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 27only 1 spring in 10 still has a frost later
  • Typical last frostMay 1450% chance of a frost after it
  • Typical first fall frostSeptember 2650% chance of a frost before it
  • Frost-free season134 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Old Fort Laramie, WYSpring: a frost after May 3 in 9 years out of 10, after May 14 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 26 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 134 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 14First frost ~Sep 26Frost season at Old Fort Laramie, WYSpring: a frost after May 3 in 9 years out of 10, after May 14 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 26 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 134 days.JFMAMJJASONDLast frost ~May 14First frost ~Sep 26
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 27September 12
50% (typical)May 14September 26
90% (likely)May 3October 7
Frost-free season (32°F, 50% chance)
134 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 11 (3 days earlier than the 30-year normal), typical first fall frost September 27 (1 day later). Frost-free season 136 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 Old Fort Laramie: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 27, 20% May 22, 30% May 19, 40% May 16, 50% May 14, 60% May 11, 70% May 8, 80% May 6, 90% May 3. Observed last spring frost in recent years: 2022 May 22, 2023 May 7, 2024 May 22, 2025 May 3, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 27May 14May 32022: May 222023: May 72024: May 222025: May 32026: May 19Fall at Old Fort Laramie: chance of a frost before this dateFall, chance of a frost before the date: 10% September 12, 20% September 18, 30% September 21, 40% September 23, 50% September 26, 60% September 28, 70% October 1, 80% October 4, 90% October 7. Observed first fall frost in recent years: 2022 October 8, 2023 October 7, 2024 September 23, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 12Sep 26Oct 72022: October 82023: October 72024: September 232025: 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
2021incomplete recordno data
2022May 22October 8
2023May 7October 7
2024May 22September 23
2025May 3September 6
2026May 19season not over yet

What these dates mean

The 134 days between the 50% dates in Old Fort Laramie – May 14 and September 26 – define the central window where a light frost is equally likely to have occurred or not. For a gardener this median point marks the middle of the season’s frost risk, with earlier parts of spring still carrying a high chance of a frost and later parts of fall similarly prone.

The cautious spring date for setting out tender crops is May 27, when there is only a 10 % chance that a light frost will still arrive. In the autumn the cautious date to finish harvesting tender crops is September 12, with only a 10 % chance that a light frost has already begun. By contrast, a hard frost at 28 °F is more damaging because it can kill plant tissue that survives a light frost.

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 12" 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 Old Fort Laramie, WYNumbered nearest stations: 1 — Wheatland, WY — 21 mi; 2 — Torrington, WY — 28 mi; 3 — Chugwater, WY — 34 mi; 4 — Harrison, NE — 48 mi; 5 — Harrisburg, NE — 50 mi.NE25 mi · 40 km1. Wheatland, WY — 21 mi12. Torrington, WY — 28 mi23. Chugwater, WY — 34 mi34. Harrison, NE — 48 mi45. Harrisburg, NE — 50 mi5
  1. Wheatland, WY 21 mi (34 km)
  2. Torrington, WY 28 mi (45 km)
  3. Chugwater, WY 34 mi (54 km)
  4. Harrison, NE 48 mi (77 km)
  5. Harrisburg, NE 50 mi (81 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: 42.2058, -104.5561.