U.S. Frost Dates by Weather Station

NOAA station USC00043578 · California

Frost Dates for Graton, CA

NOAA weather station Graton (USC00043578), California · elevation 200 ft (61 m) · hardiness zone 9a*

  • Lower-risk planting dateafter April 19only 1 spring in 10 still has a frost later
  • Typical last frostMarch 2050% chance of a frost after it
  • Typical first fall frostNovember 1350% chance of a frost before it
  • Frost-free season240 daystypical year, 32°F
  • Hardiness zone9acalculated*

The year at a glance

Frost season at Graton, CASpring: a frost after February 12 in 9 years out of 10, after March 20 in half of the years, after April 19 in 1 year out of 10. Fall: the first frost comes before October 26 in 1 year out of 10, before November 13 in half of the years, before December 6 in 9 years out of 10. Typical frost-free season: 240 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Mar 20First frost ~Nov 13Frost season at Graton, CASpring: a frost after February 12 in 9 years out of 10, after March 20 in half of the years, after April 19 in 1 year out of 10. Fall: the first frost comes before October 26 in 1 year out of 10, before November 13 in half of the years, before December 6 in 9 years out of 10. Typical frost-free season: 240 days.JFMAMJJASONDLast frost ~Mar 20First frost ~Nov 13
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 19October 26
50% (typical)March 20November 13
90% (likely)February 12December 6
Frost-free season (32°F, 50% chance)
240 days
Hard frost (28°F), last in spring, 50% chance after
February 1
Hard frost (28°F), first in fall, 50% chance before
December 3

The last 15 years (2006–2020 normals)

Typical last frost March 17 (3 days earlier than the 30-year normal), typical first fall frost November 14 (1 day later). Frost-free season 239 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 Graton: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 19, 20% April 10, 30% April 3, 40% March 28, 50% March 20, 60% March 13, 70% March 6, 80% February 27, 90% February 12. Observed last spring frost in recent years: 2021 April 8, 2022 March 12, 2023 April 4, 2025 March 9, 2026 February 21.Spring: last frostChance of a frost after this date10%50%90%Feb 1Mar 1Apr 1May 1Apr 19Mar 20Feb 122021: April 82022: March 122023: April 42025: March 92026: February 21Fall at Graton: chance of a frost before this dateFall, chance of a frost before the date: 10% October 26, 20% November 1, 30% November 5, 40% November 9, 50% November 13, 60% November 18, 70% November 23, 80% November 29, 90% December 6. Observed first fall frost in recent years: 2021 December 10, 2022 November 3, 2023 October 27, 2024 November 8, 2025 December 28.Fall: first frostChance of a frost before this date10%50%90%Nov 1Dec 1Jan 1Oct 26Nov 13Dec 62021: December 102022: November 32023: October 272024: November 82025: December 28
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
2021April 8December 10
2022March 12November 3
2023April 4October 27
2024incomplete recordNovember 8
2025March 9December 28
2026February 21season not over yet

What these dates mean

April 19 is the cautious spring date in Graton, with only a 10 % chance of a light frost later. That date lets a gardener schedule the outward planting of tender crops with minimal frost risk, while the February 12 date carries a 90 % chance and would be a gamble.

The 50 % spring date is March 20; at that point a light frost is as likely as not, so it marks the median risk for early planting. The 50 % fall date is November 13, indicating even odds of a light frost before then. For hard frost, the median dates are February 1 in spring and December 3 in fall.

October 26 is the cautious fall date, with only a 10 % chance that a light frost has arrived earlier, allowing a gardener to finish harvesting tender crops. A hard frost at 28 °F matters more than a light frost at 32 °F because the lower temperature can cause more severe damage to plant tissue.

How to read the probabilities

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

  • Spring: "10% after April 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 October 26" 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 Graton, CANumbered nearest stations: 1 — near Redwood Valley, CA — 66 mi; 2 — Mount Hamilton, CA — 100 mi; 3 — near Grass Valley, CA — 111 mi; 4 — Nevada City, CA — 115 mi; 5 — Strawberry Valley, CA — 123 mi.CANV50 mi · 80 km1. near Redwood Valley, CA — 66 mi12. Mount Hamilton, CA — 100 mi23. near Grass Valley, CA — 111 mi34. Nevada City, CA — 115 mi45. Strawberry Valley, CA — 123 mi5
  1. near Redwood Valley, CA 66 mi (106 km)
  2. Mount Hamilton, CA 100 mi (162 km)
  3. near Grass Valley, CA 111 mi (178 km)
  4. Nevada City, CA 115 mi (185 km)
  5. Strawberry Valley, CA 123 mi (197 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: 38.4306, -122.8647.