U.S. Frost Dates by Weather Station

NOAA station USC00027560 · Arizona

Frost Dates for San Simon, AZ

NOAA weather station San Simon (USC00027560), Arizona · elevation 3580 ft (1091 m) · hardiness zone 8a*

  • Lower-risk planting dateafter May 4only 1 spring in 10 still has a frost later
  • Typical last frostApril 1650% chance of a frost after it
  • Typical first fall frostNovember 250% chance of a frost before it
  • Frost-free season198 daystypical year, 32°F
  • Hardiness zone8acalculated*

The year at a glance

Frost season at San Simon, AZSpring: a frost after March 31 in 9 years out of 10, after April 16 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 17 in 1 year out of 10, before November 2 in half of the years, before November 16 in 9 years out of 10. Typical frost-free season: 198 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 16First frost ~Nov 2Frost season at San Simon, AZSpring: a frost after March 31 in 9 years out of 10, after April 16 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 17 in 1 year out of 10, before November 2 in half of the years, before November 16 in 9 years out of 10. Typical frost-free season: 198 days.JFMAMJJASONDLast frost ~Apr 16First frost ~Nov 2
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.Today

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)May 4October 17
50% (typical)April 16November 2
90% (likely)March 31November 16
Frost-free season (32°F, 50% chance)
198 days
Hard frost (28°F), last in spring, 50% chance after
April 2
Hard frost (28°F), first in fall, 50% chance before
November 12

The last 15 years (2006–2020 normals)

Typical last frost April 19 (3 days later than the 30-year normal), typical first fall frost November 1 (1 day earlier). Frost-free season 194 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 San Simon: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 4, 20% April 29, 30% April 23, 40% April 20, 50% April 16, 60% April 12, 70% April 8, 80% April 4, 90% March 31. Observed last spring frost in recent years: 2022 May 13, 2025 April 20, 2026 April 23.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 4Apr 16Mar 312022: May 132025: April 202026: April 23Fall at San Simon: chance of a frost before this dateFall, chance of a frost before the date: 10% October 17, 20% October 23, 30% October 27, 40% October 31, 50% November 2, 60% November 5, 70% November 8, 80% November 12, 90% November 16. Observed first fall frost in recent years: 2021 October 13, 2023 November 2, 2024 October 21.Fall: first frostChance of a frost before this date10%50%90%Nov 1Oct 17Nov 2Nov 162021: October 132023: November 22024: October 21
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
2021incomplete recordOctober 13
2022May 13incomplete record
2023incomplete recordNovember 2
2024incomplete recordOctober 21
2025April 20incomplete record
2026April 23season not over yet

What these dates mean

The 198 days between the 50% dates in San Simon bracket the window in which light frosts are equally likely, with the median light-frost date falling on April 16 in spring and on November 2 in fall. For a gardener, these dates mean there is a 50% chance of a frost later than April 16 and a 50% chance of a frost earlier than November 2.

The cautious date for setting out tender crops in spring is May 4, when only a 10% chance of a light frost remains, while the cautious date to finish harvesting tender crops in fall is October 17, when there is only a 10% chance that a light frost has already arrived. The hard-frost 50% dates are April 2 and November 12, and a hard frost at 28 °F can damage plants that would survive a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 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 October 17" 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 San Simon, AZNumbered nearest stations: 1 — Duncan, AZ — 32 mi; 2 — Animas, NM — 36 mi; 3 — Safford, AZ — 45 mi; 4 — Cliff, NM — 56 mi; 5 — near Douglas, AZ — 62 mi.AZNM25 mi · 40 km1. Duncan, AZ — 32 mi12. Animas, NM — 36 mi23. Safford, AZ — 45 mi34. Cliff, NM — 56 mi45. near Douglas, AZ — 62 mi5
  1. Duncan, AZ 32 mi (52 km)
  2. Animas, NM 36 mi (58 km)
  3. Safford, AZ 45 mi (72 km)
  4. Cliff, NM 56 mi (91 km)
  5. near Douglas, AZ 62 mi (100 km)

Sources

* Hardiness zone 8a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 32.2933, -109.2269.