U.S. Frost Dates by Weather Station

NOAA station USC00482725 · Wyoming

Frost Dates for Dull Center, WY

NOAA weather station Dull Center 1 SE (USC00482725), Wyoming · elevation 4415 ft (1346 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 28only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season133 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Dull Center, WYSpring: a frost after May 3 in 9 years out of 10, after May 15 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 27 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 133 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 27Frost season at Dull Center, WYSpring: a frost after May 3 in 9 years out of 10, after May 15 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 27 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 133 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 27
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 28September 13
50% (typical)May 15September 27
90% (likely)May 3October 9
Frost-free season (32°F, 50% chance)
133 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 6

The last 15 years (2006–2020 normals)

Typical last frost May 14 (1 day earlier than the 30-year normal), typical first fall frost September 29 (2 days later). Frost-free season 135 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 Dull Center: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 28, 20% May 24, 30% May 20, 40% May 17, 50% May 15, 60% May 12, 70% May 10, 80% May 7, 90% May 3.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 28May 15May 3Fall at Dull Center: chance of a frost before this dateFall, chance of a frost before the date: 10% September 13, 20% September 19, 30% September 21, 40% September 24, 50% September 27, 60% September 30, 70% October 2, 80% October 5, 90% October 9. Observed first fall frost in recent years: 2021 September 22.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 13Sep 27Oct 92021: September 22
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 recordSeptember 22
2022no datano data
2023no datano data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

The cautious fall date for finishing the harvest in Dull Center is September 13, when there is only a 10% chance that a light frost has arrived.

For tender spring crops the cautious date is May 28, which carries a 10% chance of a light frost occurring later; planting earlier on May 3 involves a 90% chance and is a gamble. The 50% dates—May 15 in spring and September 27 in fall—represent the median point at which a light frost is equally likely to have happened or not, giving gardeners a statistical midpoint for planning.

Hard frost at 28 °F can injure plant tissue more severely than a light frost at 32 °F, making those dates especially critical. The median hard-frost dates are May 3 for spring and October 6 for fall, marking the point where a 28 °F frost is equally probable.

How to read the probabilities

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

  • Spring: "10% after May 28" 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 13" 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 Dull Center, WYNumbered nearest stations: 1 — Redbird, WY — 36 mi; 2 — Wright, WY — 45 mi; 3 — Dillinger, WY — 48 mi; 4 — Newcastle, WY — 49 mi; 5 — Upton, WY — 50 mi.WYSD25 mi · 40 km1. Redbird, WY — 36 mi12. Wright, WY — 45 mi23. Dillinger, WY — 48 mi34. Newcastle, WY — 49 mi45. Upton, WY — 50 mi5
  1. Redbird, WY 36 mi (58 km)
  2. Wright, WY 45 mi (72 km)
  3. Dillinger, WY 48 mi (77 km)
  4. Newcastle, WY 49 mi (79 km)
  5. Upton, WY 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: 43.4117, -104.9614.