U.S. Frost Dates by Weather Station

NOAA station USW00024027 · Wyoming

Frost Dates for Rock Springs, WY

NOAA weather station Rock Springs Airport (USW00024027), Wyoming · elevation 6741 ft (2055 m) · hardiness zone 5b*

  • Lower-risk planting dateafter June 9only 1 spring in 10 still has a frost later
  • Typical last frostMay 2250% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season126 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Rock Springs, WYSpring: a frost after May 5 in 9 years out of 10, after May 22 in half of the years, after June 9 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 9 in 9 years out of 10. Typical frost-free season: 126 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 22First frost ~Sep 28Frost season at Rock Springs, WYSpring: a frost after May 5 in 9 years out of 10, after May 22 in half of the years, after June 9 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 9 in 9 years out of 10. Typical frost-free season: 126 days.JFMAMJJASONDLast frost ~May 22First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 9September 14
50% (typical)May 22September 28
90% (likely)May 5October 9
Frost-free season (32°F, 50% chance)
126 days
Hard frost (28°F), last in spring, 50% chance after
May 7
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 22 (same as the 30-year normal), typical first fall frost September 30 (2 days later). Frost-free season 129 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 Rock Springs: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 9, 20% June 3, 30% May 31, 40% May 26, 50% May 22, 60% May 18, 70% May 15, 80% May 10, 90% May 5. Observed last spring frost in recent years: 2021 May 12, 2022 June 1, 2023 May 7, 2024 May 24, 2025 May 20, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 9May 22May 52021: May 122022: June 12023: May 72024: May 242025: May 202026: May 22Fall at Rock Springs: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 20, 30% September 23, 40% September 25, 50% September 28, 60% September 30, 70% October 2, 80% October 4, 90% October 9. Observed first fall frost in recent years: 2021 September 21, 2022 October 16, 2023 October 7, 2024 October 18, 2025 October 7.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 28Oct 92021: September 212022: October 162023: October 72024: October 182025: October 7
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 12September 21
2022June 1October 16
2023May 7October 7
2024May 24October 18
2025May 20October 7
2026May 22season not over yet

What these dates mean

June 9 is the cautious spring light-frost date for Rock Springs, with only a 10 % chance of a frost later than that day. Planting tender crops after this date lets a gardener expect a low risk of frost damage.

The 50 % light-frost dates are May 22 for spring and September 28 for fall; each marks the point where a frost is equally likely to occur later (spring) or earlier (fall). September 14 is the cautious fall light-frost date, carrying a 10 % chance that a frost has already arrived, and therefore guides when to finish harvesting tender crops. The interval between the two 32°F 50 % dates spans 126 days, based on 29 years of record observations.

A hard frost at 28 °F, shown by the median dates May 7 and October 5, can injure plants that survive a light frost at 32 °F, making it a more critical concern.

How to read the probabilities

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

  • Spring: "10% after June 9" 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 Rock Springs, WYNumbered nearest stations: 1 — Flaming Gorge, UT — 49 mi; 2 — Baggs, WY — 82 mi; 3 — near Lander, WY — 86 mi; 4 — Jensen, UT — 87 mi; 5 — Jeffrey City, WY — 88 mi.WYCOUTID50 mi · 80 km1. Flaming Gorge, UT — 49 mi12. Baggs, WY — 82 mi23. near Lander, WY — 86 mi34. Jensen, UT — 87 mi45. Jeffrey City, WY — 88 mi5
  1. Flaming Gorge, UT 49 mi (80 km)
  2. Baggs, WY 82 mi (132 km)
  3. near Lander, WY 86 mi (138 km)
  4. Jensen, UT 87 mi (139 km)
  5. Jeffrey City, WY 88 mi (142 km)

Sources

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

Station coordinates: 41.5944, -109.0528.