U.S. Frost Dates by Weather Station

NOAA station USC00420849 · Utah

Frost Dates for Boulder, UT

NOAA weather station Boulder (USC00420849), Utah · elevation 6650 ft (2027 m) · hardiness zone 7a*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 450% chance of a frost after it
  • Typical first fall frostOctober 1450% chance of a frost before it
  • Frost-free season160 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season at Boulder, UTSpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 14 in half of the years, before October 29 in 9 years out of 10. Typical frost-free season: 160 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 4First frost ~Oct 14Frost season at Boulder, UTSpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 14 in half of the years, before October 29 in 9 years out of 10. Typical frost-free season: 160 days.JFMAMJJASONDLast frost ~May 4First frost ~Oct 14
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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 25September 30
50% (typical)May 4October 14
90% (likely)April 20October 29
Frost-free season (32°F, 50% chance)
160 days
Hard frost (28°F), last in spring, 50% chance after
April 23
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost May 5 (1 day later than the 30-year normal), typical first fall frost October 12 (2 days earlier). Frost-free season 160 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 Boulder: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 17, 30% May 12, 40% May 7, 50% May 4, 60% April 30, 70% April 28, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 May 23, 2022 May 9, 2023 April 26, 2025 April 28, 2026 April 28.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 4Apr 202021: May 232022: May 92023: April 262025: April 282026: April 28Fall at Boulder: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 4, 30% October 7, 40% October 11, 50% October 14, 60% October 17, 70% October 20, 80% October 23, 90% October 29. Observed first fall frost in recent years: 2021 October 12, 2022 October 24, 2023 October 3, 2024 October 30, 2025 October 16.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 14Oct 292021: October 122022: October 242023: October 32024: October 302025: October 16
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 23October 12
2022May 9October 24
2023April 26October 3
2024incomplete recordOctober 30
2025April 28October 16
2026April 28season not over yet

What these dates mean

May 25 is the cautious spring date for Boulder, Utah, with only a 10% chance of a light frost after that day. It allows a gardener to set out tender crops with minimal risk.

The median light-frost dates are May 4 in spring and October 14 in fall; each represents a 50% chance of frost either later (spring) or earlier (fall) and is not a frost date. The median hard-frost dates are April 23 and October 23, indicating when a 28°F frost is equally likely to have occurred or not.

September 30 serves as the cautious fall date, carrying only a 10% chance that a light frost has already arrived, so it is the date to finish harvesting tender crops. A hard frost at 28°F matters more than a light frost at 32°F because the lower temperature can cause more severe plant injury.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 30" 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 Boulder, UTNumbered nearest stations: 1 — Escalante, UT — 14 mi; 2 — Capitol Reef National Park, UT — 28 mi; 3 — Bryce Canyon National Park Headquarters, UT — 45 mi; 4 — Alton, UT — 66 mi; 5 — near Richfield, UT — 69 mi.UT25 mi · 40 km1. Escalante, UT — 14 mi12. Capitol Reef National Park, UT — 28 mi23. Bryce Canyon National Park Headquarters, UT — 45 mi34. Alton, UT — 66 mi45. near Richfield, UT — 69 mi5
  1. Escalante, UT 14 mi (22 km)
  2. Capitol Reef National Park, UT 28 mi (45 km)
  3. Bryce Canyon National Park Headquarters, UT 45 mi (72 km)
  4. Alton, UT 66 mi (107 km)
  5. near Richfield, UT 69 mi (111 km)

Sources

* Hardiness zone 7a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 37.905, -111.42.