U.S. Frost Dates by Weather Station

NOAA station USC00420072 · Utah

Frost Dates for Alta, UT

NOAA weather station Alta (USC00420072), Utah · elevation 8710 ft (2655 m) · hardiness zone 6a*

  • Lower-risk planting dateafter June 27only 1 spring in 10 still has a frost later
  • Typical last frostJune 1150% chance of a frost after it
  • Typical first fall frostSeptember 1850% chance of a frost before it
  • Frost-free season98 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Alta, UTSpring: a frost after May 26 in 9 years out of 10, after June 11 in half of the years, after June 27 in 1 year out of 10. Fall: the first frost comes before September 3 in 1 year out of 10, before September 18 in half of the years, before September 29 in 9 years out of 10. Typical frost-free season: 98 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 11First frost ~Sep 18Frost season at Alta, UTSpring: a frost after May 26 in 9 years out of 10, after June 11 in half of the years, after June 27 in 1 year out of 10. Fall: the first frost comes before September 3 in 1 year out of 10, before September 18 in half of the years, before September 29 in 9 years out of 10. Typical frost-free season: 98 days.JFMAMJJASONDLast frost ~Jun 11First frost ~Sep 18
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 27September 3
50% (typical)June 11September 18
90% (likely)May 26September 29
Frost-free season (32°F, 50% chance)
98 days
Hard frost (28°F), last in spring, 50% chance after
June 1
Hard frost (28°F), first in fall, 50% chance before
September 27

The last 15 years (2006–2020 normals)

Typical last frost June 12 (1 day later than the 30-year normal), typical first fall frost September 20 (2 days later). Frost-free season 99 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 Alta: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 27, 20% June 22, 30% June 18, 40% June 15, 50% June 11, 60% June 8, 70% June 5, 80% June 1, 90% May 26. Observed last spring frost in recent years: 2021 June 11, 2022 June 20, 2023 May 11, 2024 June 18, 2025 June 23, 2026 June 29.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jun 27Jun 11May 262021: June 112022: June 202023: May 112024: June 182025: June 232026: June 29Fall at Alta: chance of a frost before this dateFall, chance of a frost before the date: 10% September 3, 20% September 9, 30% September 13, 40% September 16, 50% September 18, 60% September 21, 70% September 23, 80% September 26, 90% September 29. Observed first fall frost in recent years: 2021 September 19, 2022 October 1, 2023 September 23, 2024 September 13, 2025 October 4.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 3Sep 18Sep 292021: September 192022: October 12023: September 232024: September 132025: October 4
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
2021June 11September 19
2022June 20October 1
2023May 11September 23
2024June 18September 13
2025June 23October 4
2026June 29season not over yet

What these dates mean

September 3 is the cautious fall date in Alta for finishing the harvest, carrying only a 10% chance that a light frost has arrived earlier. For tender crops the conservative choice in spring is June 27, when the risk of a light frost later than that day is also 10%.

The 50% date is June 11, indicating a 50% chance of a light frost later than this date, while the 50% date is September 18, indicating a 50% chance of a light frost earlier than this date. These median points help a gardener gauge the middle of the frost probability range.

Hard frost at 28°F is more damaging than a light frost at 32°F because the lower temperature can freeze plant tissue that would survive a milder chill.

How to read the probabilities

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

  • Spring: "10% after June 27" 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 3" 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 Alta, UTNumbered nearest stations: 1 — Cottonwood Weir, UT — 8 mi; 2 — near Midway, UT — 14 mi; 3 — Pleasant Grove, UT — 16 mi; 4 — near Silver Summit, UT — 18 mi; 5 — Kamas, UT — 19 mi.WY25 mi · 40 km1. Cottonwood Weir, UT — 8 mi12. near Midway, UT — 14 mi23. Pleasant Grove, UT — 16 mi34. near Silver Summit, UT — 18 mi45. Kamas, UT — 19 mi5
  1. Cottonwood Weir, UT 8 mi (13 km)
  2. near Midway, UT 14 mi (23 km)
  3. Pleasant Grove, UT 16 mi (26 km)
  4. near Silver Summit, UT 18 mi (29 km)
  5. Kamas, UT 19 mi (31 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 40.5906, -111.6369.