U.S. Frost Dates by Weather Station

NOAA station USC00484925 · Wyoming

Frost Dates for Jeffrey City, WY

NOAA weather station Jeffrey City (USC00484925), Wyoming · elevation 6319 ft (1926 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 16only 1 spring in 10 still has a frost later
  • Typical last frostJune 150% chance of a frost after it
  • Typical first fall frostSeptember 1350% chance of a frost before it
  • Frost-free season104 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Jeffrey City, WYSpring: a frost after May 17 in 9 years out of 10, after June 1 in half of the years, after June 16 in 1 year out of 10. Fall: the first frost comes before September 1 in 1 year out of 10, before September 13 in half of the years, before September 28 in 9 years out of 10. Typical frost-free season: 104 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 1First frost ~Sep 13Frost season at Jeffrey City, WYSpring: a frost after May 17 in 9 years out of 10, after June 1 in half of the years, after June 16 in 1 year out of 10. Fall: the first frost comes before September 1 in 1 year out of 10, before September 13 in half of the years, before September 28 in 9 years out of 10. Typical frost-free season: 104 days.JFMAMJJASONDLast frost ~Jun 1First frost ~Sep 13
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 16September 1
50% (typical)June 1September 13
90% (likely)May 17September 28
Frost-free season (32°F, 50% chance)
104 days
Hard frost (28°F), last in spring, 50% chance after
May 17
Hard frost (28°F), first in fall, 50% chance before
September 24

The last 15 years (2006–2020 normals)

Typical last frost May 30 (2 days earlier than the 30-year normal), typical first fall frost September 12 (1 day earlier). Frost-free season 105 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 Jeffrey City: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 16, 20% June 10, 30% June 6, 40% June 3, 50% June 1, 60% May 30, 70% May 26, 80% May 22, 90% May 17. Observed last spring frost in recent years: 2021 May 13, 2022 June 1, 2023 May 11, 2024 June 1, 2025 June 23, 2026 June 15.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jun 16Jun 1May 172021: May 132022: June 12023: May 112024: June 12025: June 232026: June 15Fall at Jeffrey City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 1, 20% September 4, 30% September 8, 40% September 10, 50% September 13, 60% September 16, 70% September 19, 80% September 23, 90% September 28. Observed first fall frost in recent years: 2021 September 21, 2022 September 14, 2023 September 24, 2025 September 18.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 1Sep 13Sep 282021: September 212022: September 142023: September 242025: September 18
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 13September 21
2022June 1September 14
2023May 11September 24
2024June 1incomplete record
2025June 23September 18
2026June 15season not over yet

What these dates mean

The cautious fall date in Jeffrey City for finishing the harvest is September 1, when there is only a 10 % chance that a light frost has arrived earlier.

The cautious spring date for setting out tender crops is June 16, with a 10 % chance of a light frost later. For a gardener, the 50% date is June 1, with a 50 % chance of a light frost later than this date, and the median hard-frost date in spring is May 17.

The cautious fall date for ending tender-crop harvest is September 1, with only a 10 % chance of a light frost earlier. The 50% date is September 13, with a 50 % chance of a light frost earlier than this date, and the median hard-frost date in fall is September 24. A hard frost at 28 °F can damage plants that survive a light frost at 32 °F, making it a more critical threshold.

How to read the probabilities

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

  • Spring: "10% after June 16" 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 1" 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 Jeffrey City, WYNumbered nearest stations: 1 — near Lander, WY — 51 mi; 2 — Rawlins, WY — 57 mi; 3 — Casper, WY — 75 mi; 4 — Bates Creek #2, WY — 75 mi; 5 — Thermopolis, WY — 82 mi.WY50 mi · 80 km1. near Lander, WY — 51 mi12. Rawlins, WY — 57 mi23. Casper, WY — 75 mi34. Bates Creek #2, WY — 75 mi45. Thermopolis, WY — 82 mi5
  1. near Lander, WY 51 mi (82 km)
  2. Rawlins, WY 57 mi (92 km)
  3. Casper, WY 75 mi (120 km)
  4. Bates Creek #2, WY 75 mi (121 km)
  5. Thermopolis, WY 82 mi (132 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: 42.4942, -107.8292.