U.S. Frost Dates by Weather Station

NOAA station USC00048353 · California

Frost Dates for Sonora, CA

NOAA weather station Sonora (USC00048353), California · elevation 1675 ft (511 m) · hardiness zone 9a*

  • Lower-risk planting dateafter April 30only 1 spring in 10 still has a frost later
  • Typical last frostApril 950% chance of a frost after it
  • Typical first fall frostNovember 950% chance of a frost before it
  • Frost-free season213 daystypical year, 32°F
  • Hardiness zone9acalculated*

The year at a glance

Frost season at Sonora, CASpring: a frost after March 15 in 9 years out of 10, after April 9 in half of the years, after April 30 in 1 year out of 10. Fall: the first frost comes before October 19 in 1 year out of 10, before November 9 in half of the years, before November 27 in 9 years out of 10. Typical frost-free season: 213 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 9First frost ~Nov 9Frost season at Sonora, CASpring: a frost after March 15 in 9 years out of 10, after April 9 in half of the years, after April 30 in 1 year out of 10. Fall: the first frost comes before October 19 in 1 year out of 10, before November 9 in half of the years, before November 27 in 9 years out of 10. Typical frost-free season: 213 days.JFMAMJJASONDLast frost ~Apr 9First frost ~Nov 9
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)April 30October 19
50% (typical)April 9November 9
90% (likely)March 15November 27
Frost-free season (32°F, 50% chance)
213 days
Hard frost (28°F), last in spring, 50% chance after
March 4
Hard frost (28°F), first in fall, 50% chance before
November 27

The last 15 years (2006–2020 normals)

Typical last frost April 9 (same as the 30-year normal), typical first fall frost November 12 (3 days later). Frost-free season 217 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 Sonora: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 30, 20% April 23, 30% April 18, 40% April 13, 50% April 9, 60% April 5, 70% April 1, 80% March 25, 90% March 15. Observed last spring frost in recent years: 2021 March 17, 2023 April 20.Spring: last frostChance of a frost after this date10%50%90%Mar 1Apr 1May 1Apr 30Apr 9Mar 152021: March 172023: April 20Fall at Sonora: chance of a frost before this dateFall, chance of a frost before the date: 10% October 19, 20% October 27, 30% November 1, 40% November 4, 50% November 9, 60% November 12, 70% November 17, 80% November 21, 90% November 27. Observed first fall frost in recent years: 2024 November 12.Fall: first frostChance of a frost before this date10%50%90%Nov 1Dec 1Oct 19Nov 9Nov 272024: November 12
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
2021March 17incomplete record
2022incomplete recordincomplete record
2023April 20incomplete record
2024incomplete recordNovember 12
2025incomplete recordincomplete record
2026incomplete recordseason not over yet

What these dates mean

April 30 marks the cautious spring date for tender crops in Sonora, giving gardeners a point at which only a 10 % chance of a light frost remains. The 50 % date is April 9, meaning the odds of a frost later than that day are even, while planting on March 15 carries a 90 % chance of a frost and is a gamble. The 50 % hard-frost date is March 4, a reference for when an even chance of a 28 °F freeze occurs.

For the autumn window, October 19 is the cautious fall date, when there is only a 10 % chance that a light frost has arrived, allowing growers to finish harvesting tender crops. The 50 % date is November 9, and the 50 % hard-frost date is November 27, indicating an even chance of a 28 °F freeze. A hard frost at 28 °F can damage 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 April 30" 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 19" 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 Sonora, CANumbered nearest stations: 1 — Calaveras Big Trees, CA — 22 mi; 2 — Cherry Valley Dam, CA — 26 mi; 3 — Lee Vining, CA — 69 mi; 4 — Minden, NV — 76 mi; 5 — Auberry, CA — 77 mi.NV50 mi · 80 km1. Calaveras Big Trees, CA — 22 mi12. Cherry Valley Dam, CA — 26 mi23. Lee Vining, CA — 69 mi34. Minden, NV — 76 mi45. Auberry, CA — 77 mi5
  1. Calaveras Big Trees, CA 22 mi (35 km)
  2. Cherry Valley Dam, CA 26 mi (41 km)
  3. Lee Vining, CA 69 mi (111 km)
  4. Minden, NV 76 mi (122 km)
  5. Auberry, CA 77 mi (124 km)

Sources

* Hardiness zone 9a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 37.9672, -120.3872.