U.S. Frost Dates by Weather Station

NOAA station USC00420730 · Utah

Frost Dates for Black Rock, UT

NOAA weather station Black Rock (USC00420730), Utah · elevation 4916 ft (1498 m) · hardiness zone 5b*

  • Lower-risk planting dateafter June 11only 1 spring in 10 still has a frost later
  • Typical last frostMay 2350% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season124 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Black Rock, UTSpring: a frost after May 5 in 9 years out of 10, after May 23 in half of the years, after June 11 in 1 year out of 10. Fall: the first frost comes before September 14 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: 124 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 23First frost ~Sep 27Frost season at Black Rock, UTSpring: a frost after May 5 in 9 years out of 10, after May 23 in half of the years, after June 11 in 1 year out of 10. Fall: the first frost comes before September 14 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: 124 days.JFMAMJJASONDLast frost ~May 23First 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)June 11September 14
50% (typical)May 23September 27
90% (likely)May 5October 9
Frost-free season (32°F, 50% chance)
124 days
Hard frost (28°F), last in spring, 50% chance after
May 7
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 20 (3 days earlier than the 30-year normal), typical first fall frost September 29 (2 days later). Frost-free season 128 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 Black Rock: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 11, 20% June 5, 30% June 1, 40% May 28, 50% May 23, 60% May 19, 70% May 15, 80% May 10, 90% May 5. Observed last spring frost in recent years: 2021 June 11, 2022 May 30, 2023 May 12, 2024 May 22, 2025 May 20, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 11May 23May 52021: June 112022: May 302023: May 122024: May 222025: May 202026: May 20Fall at Black Rock: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 19, 30% September 22, 40% September 24, 50% September 27, 60% September 30, 70% October 1, 80% October 4, 90% October 9. Observed first fall frost in recent years: 2021 September 21, 2022 October 8, 2023 October 13, 2024 October 14, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 27Oct 92021: September 212022: October 82023: October 132024: October 142025: October 6
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 21
2022May 30October 8
2023May 12October 13
2024May 22October 14
2025May 20October 6
2026May 20season not over yet

What these dates mean

June 11 is the cautious spring light-frost date for Black Rock; with only a 10 % chance of a frost later, a gardener can plan to set out tender crops after that day.

The 50 % dates—May 23 in spring and September 27 in fall—mark the point at which a light frost is equally likely to occur before or after, giving a clear reference for risk. The median hard-frost dates are May 7 and October 5; a 28 °F frost can damage plants that survive a light frost.

September 14 is the cautious fall light-frost date; with only a 10 % chance of a frost earlier, it signals the latest day a gardener should finish harvesting tender crops. The record spans 28 years, and the interval between the two 32 °F 50 % dates is 124 days.

How to read the probabilities

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

  • Spring: "10% after June 11" 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 Black Rock, UTNumbered nearest stations: 1 — Deseret, UT — 43 mi; 2 — near Richfield, UT — 47 mi; 3 — Eskdale, UT — 60 mi; 4 — Manti, UT — 81 mi; 5 — Partoun, UT — 81 mi.UT25 mi · 40 km1. Deseret, UT — 43 mi12. near Richfield, UT — 47 mi23. Eskdale, UT — 60 mi34. Manti, UT — 81 mi45. Partoun, UT — 81 mi5
  1. Deseret, UT 43 mi (70 km)
  2. near Richfield, UT 47 mi (76 km)
  3. Eskdale, UT 60 mi (97 km)
  4. Manti, UT 81 mi (130 km)
  5. Partoun, UT 81 mi (130 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 38.7075, -112.9539.