U.S. Frost Dates by Weather Station

NOAA station USC00489805 · Wyoming

Frost Dates for Wright, WY

NOAA weather station Wright 12 W (USC00489805), Wyoming · elevation 5020 ft (1530 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 8only 1 spring in 10 still has a frost later
  • Typical last frostMay 2550% chance of a frost after it
  • Typical first fall frostSeptember 2350% chance of a frost before it
  • Frost-free season120 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Wright, WYSpring: a frost after May 14 in 9 years out of 10, after May 25 in half of the years, after June 8 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 23 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 120 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 25First frost ~Sep 23Frost season at Wright, WYSpring: a frost after May 14 in 9 years out of 10, after May 25 in half of the years, after June 8 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 23 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 120 days.JFMAMJJASONDLast frost ~May 25First 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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 8September 8
50% (typical)May 25September 23
90% (likely)May 14October 5
Frost-free season (32°F, 50% chance)
120 days
Hard frost (28°F), last in spring, 50% chance after
May 13
Hard frost (28°F), first in fall, 50% chance before
October 2

The last 15 years (2006–2020 normals)

Typical last frost May 25 (same as the 30-year normal), typical first fall frost September 23. Frost-free season 119 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 Wright: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 8, 20% June 3, 30% May 31, 40% May 28, 50% May 25, 60% May 23, 70% May 20, 80% May 17, 90% May 14.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 8May 25May 14Fall at Wright: chance of a frost before this dateFall, chance of a frost before the date: 10% September 8, 20% September 14, 30% September 17, 40% September 21, 50% September 23, 60% September 26, 70% September 28, 80% October 1, 90% October 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 8Sep 23Oct 5
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.

What these dates mean

September 8 is the cautious fall date in Wright for finishing the harvest of tender crops, because only a 10 % chance of a light frost has arrived by then. A similarly low-risk point in spring is June 8, when the probability of a 32 °F frost later in the season is also 10 %. A cautious plan for tender crops therefore uses June 8 in spring and September 8 in fall. Planting before June 8 or after September 8 raises the risk substantially, as the 90 % gamble dates are May 14 in spring and October 5 in fall.

The 50 % dates—May 25 for spring and September 23 for fall—mark the median point where a light frost is as likely as not; they are not frost dates themselves but show even odds for frost in spring and for frost in fall. A hard frost, defined at 28 °F, is more damaging than a light frost at 32 °F, so the median hard-frost dates of May 13 and October 2 are useful reference points for gardeners concerned about severe cold.

How to read the probabilities

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

  • Spring: "10% after June 8" 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 8" 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 Wright, WYNumbered nearest stations: 1 — Midwest, WY — 36 mi; 2 — Dillinger, WY — 39 mi; 3 — Dull Center, WY — 45 mi; 4 — Kaycee, WY — 45 mi; 5 — Upton, WY — 61 mi.25 mi · 40 km1. Midwest, WY — 36 mi12. Dillinger, WY — 39 mi23. Dull Center, WY — 45 mi34. Kaycee, WY — 45 mi45. Upton, WY — 61 mi5
  1. Midwest, WY 36 mi (57 km)
  2. Dillinger, WY 39 mi (63 km)
  3. Dull Center, WY 45 mi (72 km)
  4. Kaycee, WY 45 mi (73 km)
  5. Upton, WY 61 mi (98 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: 43.7472, -105.7331.