U.S. Frost Dates by Weather Station

NOAA station USC00421759 · Utah

Frost Dates for Cottonwood Weir, UT

NOAA weather station Cottonwood Weir (USC00421759), Utah · elevation 4986 ft (1520 m) · hardiness zone 7a*

  • Lower-risk planting dateafter May 30only 1 spring in 10 still has a frost later
  • Typical last frostApril 2950% chance of a frost after it
  • Typical first fall frostOctober 2250% chance of a frost before it
  • Frost-free season174 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season at Cottonwood Weir, UTSpring: a frost after April 10 in 9 years out of 10, after April 29 in half of the years, after May 30 in 1 year out of 10. Fall: the first frost comes before October 6 in 1 year out of 10, before October 22 in half of the years, before November 7 in 9 years out of 10. Typical frost-free season: 174 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 29First frost ~Oct 22Frost season at Cottonwood Weir, UTSpring: a frost after April 10 in 9 years out of 10, after April 29 in half of the years, after May 30 in 1 year out of 10. Fall: the first frost comes before October 6 in 1 year out of 10, before October 22 in half of the years, before November 7 in 9 years out of 10. Typical frost-free season: 174 days.JFMAMJJASONDLast frost ~Apr 29First frost ~Oct 22
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)May 30October 6
50% (typical)April 29October 22
90% (likely)April 10November 7
Frost-free season (32°F, 50% chance)
174 days
Hard frost (28°F), last in spring, 50% chance after
April 12
Hard frost (28°F), first in fall, 50% chance before
November 1

The last 15 years (2006–2020 normals)

Typical last frost April 30 (1 day later than the 30-year normal), typical first fall frost October 23 (1 day later). Frost-free season 175 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 Cottonwood Weir: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 30, 20% May 15, 30% May 8, 40% May 2, 50% April 29, 60% April 25, 70% April 21, 80% April 17, 90% April 10. Observed last spring frost in recent years: 2021 April 20, 2022 April 30, 2023 April 20, 2024 May 9, 2025 April 19, 2026 April 25.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Jun 1May 30Apr 29Apr 102021: April 202022: April 302023: April 202024: May 92025: April 192026: April 25Fall at Cottonwood Weir: chance of a frost before this dateFall, chance of a frost before the date: 10% October 6, 20% October 12, 30% October 16, 40% October 19, 50% October 22, 60% October 26, 70% October 29, 80% November 2, 90% November 7. Observed first fall frost in recent years: 2021 November 17, 2022 October 24, 2023 October 27, 2024 September 22, 2025 October 19.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 6Oct 22Nov 72021: November 172022: October 242023: October 272024: September 222025: October 19
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
2021April 20November 17
2022April 30October 24
2023April 20October 27
2024May 9September 22
2025April 19October 19
2026April 25season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 10 carries a 90 % chance that a light frost will occur later, making it a gamble for producers at Cottonwood Weir.

The 50 % dates—April 29 in spring and October 22 in fall—represent the point at which a light frost is equally likely to have happened or not, giving gardeners a clear sense of the median risk. A cautious plan uses the May 30 date, with only a 10 % chance of a later frost, for sowing tender crops, and the October 6 date, also with a 10 % chance of an earlier frost, for finishing harvests. The hard-frost 50 % dates are April 12 and November 1, marking the median moments when temperatures may reach 28 °F.

Because a hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F, it represents a more serious threat to tender crops.

How to read the probabilities

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

  • Spring: "10% after May 30" 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 October 6" 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 Cottonwood Weir, UTNumbered nearest stations: 1 — Alta, UT — 8 mi; 2 — Pleasant Grove, UT — 18 mi; 3 — near Bountiful, UT — 19 mi; 4 — near Midway, UT — 20 mi; 5 — near Silver Summit, UT — 23 mi.WY25 mi · 40 km1. Alta, UT — 8 mi12. Pleasant Grove, UT — 18 mi23. near Bountiful, UT — 19 mi34. near Midway, UT — 20 mi45. near Silver Summit, UT — 23 mi5
  1. Alta, UT 8 mi (13 km)
  2. Pleasant Grove, UT 18 mi (28 km)
  3. near Bountiful, UT 19 mi (31 km)
  4. near Midway, UT 20 mi (32 km)
  5. near Silver Summit, UT 23 mi (37 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: 40.6189, -111.7836.