U.S. Frost Dates by Weather Station

NOAA station USC00421144 · Utah

Frost Dates for Callao, UT

NOAA weather station Callao (USC00421144), Utah · elevation 4342 ft (1323 m) · hardiness zone 6b*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 1450% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season135 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Callao, UTSpring: a frost after April 29 in 9 years out of 10, after May 14 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 135 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 14First frost ~Sep 28Frost season at Callao, UTSpring: a frost after April 29 in 9 years out of 10, after May 14 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 135 days.JFMAMJJASONDLast frost ~May 14First frost ~Sep 28
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)June 4September 14
50% (typical)May 14September 28
90% (likely)April 29October 12
Frost-free season (32°F, 50% chance)
135 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 8

The last 15 years (2006–2020 normals)

Typical last frost May 12 (2 days earlier than the 30-year normal), typical first fall frost October 1 (3 days later). Frost-free season 138 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 Callao: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 29, 30% May 22, 40% May 18, 50% May 14, 60% May 11, 70% May 7, 80% May 3, 90% April 29. Observed last spring frost in recent years: 2021 May 24, 2022 June 1, 2023 April 27, 2024 May 6, 2025 April 20, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 14Apr 292021: May 242022: June 12023: April 272024: May 62025: April 202026: May 19Fall at Callao: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 20, 30% September 23, 40% September 26, 50% September 28, 60% October 1, 70% October 3, 80% October 7, 90% October 12. Observed first fall frost in recent years: 2021 September 20, 2022 October 5, 2023 October 13, 2024 October 20, 2025 October 16.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 28Oct 122021: September 202022: October 52023: October 132024: October 202025: 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 24September 20
2022June 1October 5
2023April 27October 13
2024May 6October 20
2025April 20October 16
2026May 19season not over yet

What these dates mean

The 135 days between the 50% dates in Callao, Utah, bracket the span when a light frost is as likely as not, giving gardeners a clear window for tender plant activity. The median light-frost dates are May 14 in spring and September 28 in fall; each marks the point at which the probability of a frost later (spring) or earlier (fall) is fifty percent.

For a cautious schedule, tender crops should be set out after the June 4 spring date, which carries only a ten-percent chance of a later frost, and should be finished by September 14 in fall, which has only a ten-percent chance that a frost has already arrived. A hard frost reaching 28 °F, noted by the April 30 and October 8 50% dates, can damage plants more severely than a light 32 °F frost, so its timing is the more critical concern for winter survival.

How to read the probabilities

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

  • Spring: "10% after June 4" 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 14" 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 Callao, UTNumbered nearest stations: 1 — Ibapah, UT — 17 mi; 2 — Partoun, UT — 21 mi; 3 — Lages, NV — 49 mi; 4 — Eskdale, UT — 56 mi; 5 — Wendover, UT — 59 mi.NVUT50 mi · 80 km1. Ibapah, UT — 17 mi12. Partoun, UT — 21 mi23. Lages, NV — 49 mi34. Eskdale, UT — 56 mi45. Wendover, UT — 59 mi5
  1. Ibapah, UT 17 mi (28 km)
  2. Partoun, UT 21 mi (33 km)
  3. Lages, NV 49 mi (79 km)
  4. Eskdale, UT 56 mi (90 km)
  5. Wendover, UT 59 mi (95 km)

Sources

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

Station coordinates: 39.8997, -113.7128.