U.S. Frost Dates by Weather Station

NOAA station USC00025412 · Arizona

Frost Dates for McNary, AZ

NOAA weather station McNary 2 N (USC00025412), Arizona · elevation 7340 ft (2237 m) · hardiness zone 6b*

  • Lower-risk planting dateafter June 4only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostOctober 1150% chance of a frost before it
  • Frost-free season142 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at McNary, AZSpring: a frost after May 5 in 9 years out of 10, after May 20 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 11 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 142 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Oct 11Frost season at McNary, AZSpring: a frost after May 5 in 9 years out of 10, after May 20 in half of the years, after June 4 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 11 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 142 days.JFMAMJJASONDLast frost ~May 20First frost ~Oct 11
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)June 4September 29
50% (typical)May 20October 11
90% (likely)May 5October 24
Frost-free season (32°F, 50% chance)
142 days
Hard frost (28°F), last in spring, 50% chance after
May 6
Hard frost (28°F), first in fall, 50% chance before
October 22

The last 15 years (2006–2020 normals)

Typical last frost May 18 (2 days earlier than the 30-year normal), typical first fall frost October 9 (2 days earlier). Frost-free season 146 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 McNary: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 4, 20% May 31, 30% May 26, 40% May 23, 50% May 20, 60% May 17, 70% May 14, 80% May 9, 90% May 5. Observed last spring frost in recent years: 2021 May 24, 2022 May 13, 2023 May 12, 2024 May 12, 2025 May 20, 2026 May 6.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 4May 20May 52021: May 242022: May 132023: May 122024: May 122025: May 202026: May 6Fall at McNary: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 2, 30% October 5, 40% October 8, 50% October 11, 60% October 14, 70% October 17, 80% October 20, 90% October 24. Observed first fall frost in recent years: 2021 October 11, 2022 October 17, 2023 October 13, 2024 October 19, 2025 October 17.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 11Oct 242021: October 112022: October 172023: October 132024: October 192025: October 17
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 24October 11
2022May 13October 17
2023May 12October 13
2024May 12October 19
2025May 20October 17
2026May 6season not over yet

What these dates mean

September 29 marks the cautious fall date for finishing the harvest of tender crops in McNary; only a 10 % chance exists that a light frost has arrived earlier. In the spring, June 4 serves as the cautious date for setting out tender crops, with a 10 % chance of a frost later than that day, while the 50 % date on May 20 indicates an even odds of a light frost occurring later.

The 50 % date of October 11 signals a 50 % chance of a light frost earlier than that day, guiding the latest time to plan for tender crops in the fall. The hard-frost median dates are May 6 in spring and October 22 in fall; these 28 °F thresholds are more critical because a hard frost can injure plants that would survive a 32 °F light frost.

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 29" 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 McNary, AZNumbered nearest stations: 1 — Show Low, AZ — 13 mi; 2 — Springerville, AZ — 33 mi; 3 — Saint Johns, AZ — 38 mi; 4 — Petrified Forest National Park, AZ — 47 mi; 5 — Winslow, AZ — 80 mi.AZNM25 mi · 40 km1. Show Low, AZ — 13 mi12. Springerville, AZ — 33 mi23. Saint Johns, AZ — 38 mi34. Petrified Forest National Park, AZ — 47 mi45. Winslow, AZ — 80 mi5
  1. Show Low, AZ 13 mi (22 km)
  2. Springerville, AZ 33 mi (54 km)
  3. Saint Johns, AZ 38 mi (61 km)
  4. Petrified Forest National Park, AZ 47 mi (76 km)
  5. Winslow, AZ 80 mi (129 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: 34.1142, -109.8589.