U.S. Frost Dates by Weather Station

NOAA station USW00003103 · Arizona

Frost Dates near Flagstaff, AZ

NOAA weather station Flagstaff Pulliam Airport (USW00003103), Arizona · elevation 7003 ft (2135 m) · hardiness zone 6a*

Flagstaff is the nearest town to the station (3.8 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter June 19only 1 spring in 10 still has a frost later
  • Typical last frostJune 450% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season115 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season near Flagstaff, AZSpring: a frost after May 21 in 9 years out of 10, after June 4 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 28 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 115 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 4First frost ~Sep 28Frost season near Flagstaff, AZSpring: a frost after May 21 in 9 years out of 10, after June 4 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 28 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 115 days.JFMAMJJASONDLast frost ~Jun 4First 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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 19September 16
50% (typical)June 4September 28
90% (likely)May 21October 9
Frost-free season (32°F, 50% chance)
115 days
Hard frost (28°F), last in spring, 50% chance after
May 20
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost June 1 (3 days earlier than the 30-year normal), typical first fall frost September 29 (1 day later). Frost-free season 118 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 near Flagstaff: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 19, 20% June 14, 30% June 10, 40% June 6, 50% June 4, 60% June 1, 70% May 30, 80% May 26, 90% May 21. Observed last spring frost in recent years: 2021 May 25, 2022 June 20, 2023 June 24, 2024 May 22, 2025 May 20, 2026 May 30.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jun 19Jun 4May 212021: May 252022: June 202023: June 242024: May 222025: May 202026: May 30Fall near Flagstaff: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 20, 30% September 23, 40% September 26, 50% September 28, 60% October 1, 70% October 2, 80% October 5, 90% October 9. Observed first fall frost in recent years: 2021 September 30, 2022 October 13, 2023 October 3, 2024 October 18, 2025 October 5.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 28Oct 92021: September 302022: October 132023: October 32024: October 182025: October 5
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 25September 30
2022June 20October 13
2023June 24October 3
2024May 22October 18
2025May 20October 5
2026May 30season not over yet

What these dates mean

Setting out tender crops on the early spring date risks a 90% chance of a light frost later than that day in the Flagstaff area. The early spring date is May 21, when frost is very likely, while the cautious spring date is June 19, which carries only a 10% chance. The 50% date in spring is June 4; a gardener has an even chance of a light frost later than that day. The 50% hard-frost date is May 20, marking the point at which a 28 °F frost is equally likely to have occurred or not.

In fall, the cautious date to finish tender crops is September 16, when only a 10% chance exists that a light frost has already arrived. Waiting until October 9 is a gamble, because there is a 90% chance a light frost will have come earlier. The 50% fall date is September 28, giving an even chance of a frost earlier than that day, and the 50% hard-frost date is October 9. A hard frost at 28 °F can damage or kill plants that survive a light 32 °F 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 19" 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 16" 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 Flagstaff, AZNumbered nearest stations: 1 — Wupatki National Monument, AZ — 31 mi; 2 — Jerome, AZ — 37 mi; 3 — near Camp Verde, AZ — 38 mi; 4 — Winslow, AZ — 54 mi; 5 — Prescott, AZ — 59 mi.AZ25 mi · 40 km1. Wupatki National Monument, AZ — 31 mi12. Jerome, AZ — 37 mi23. near Camp Verde, AZ — 38 mi34. Winslow, AZ — 54 mi45. Prescott, AZ — 59 mi5
  1. Wupatki National Monument, AZ 31 mi (50 km)
  2. Jerome, AZ 37 mi (60 km)
  3. near Camp Verde, AZ 38 mi (61 km)
  4. Winslow, AZ 54 mi (87 km)
  5. Prescott, AZ 59 mi (95 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: 35.1442, -111.6664.