U.S. Frost Dates by Weather Station

NOAA station USC00043573 · California

Frost Dates near Grass Valley, CA

NOAA weather station Grass Valley #2 (USC00043573), California · elevation 2400 ft (732 m) · hardiness zone 9a*

Grass Valley is the nearest town to the station (1.1 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 April 30only 1 spring in 10 still has a frost later
  • Typical last frostApril 1050% chance of a frost after it
  • Typical first fall frostNovember 1350% chance of a frost before it
  • Frost-free season215 daystypical year, 32°F
  • Hardiness zone9acalculated*

The year at a glance

Frost season near Grass Valley, CASpring: a frost after March 17 in 9 years out of 10, after April 10 in half of the years, after April 30 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 1 in 9 years out of 10. Typical frost-free season: 215 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 10First frost ~Nov 13Frost season near Grass Valley, CASpring: a frost after March 17 in 9 years out of 10, after April 10 in half of the years, after April 30 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 1 in 9 years out of 10. Typical frost-free season: 215 days.JFMAMJJASONDLast frost ~Apr 10First 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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 30October 26
50% (typical)April 10November 13
90% (likely)March 17December 1
Frost-free season (32°F, 50% chance)
215 days
Hard frost (28°F), last in spring, 50% chance after
March 9
Hard frost (28°F), first in fall, 50% chance before
December 1

The last 15 years (2006–2020 normals)

Typical last frost April 10 (same as the 30-year normal), typical first fall frost November 14 (1 day later). Frost-free season 218 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 Grass Valley: 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 14, 50% April 10, 60% April 7, 70% April 3, 80% March 29, 90% March 17. Observed last spring frost in recent years: 2021 March 25, 2022 May 12, 2023 April 20, 2024 April 8, 2025 April 4, 2026 March 7.Spring: last frostChance of a frost after this date10%50%90%Mar 1Apr 1May 1Apr 30Apr 10Mar 172021: March 252022: May 122023: April 202024: April 82025: April 42026: March 7Fall near Grass Valley: 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 10, 50% November 13, 60% November 17, 70% November 21, 80% November 26, 90% December 1. Observed first fall frost in recent years: 2021 November 24, 2022 November 3, 2023 October 30, 2024 November 16, 2025 December 1.Fall: first frostChance of a frost before this date10%50%90%Nov 1Dec 1Oct 26Nov 13Dec 12021: November 242022: November 32023: October 302024: November 162025: December 1
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 25November 24
2022May 12November 3
2023April 20October 30
2024April 8November 16
2025April 4December 1
2026March 7season not over yet

What these dates mean

The cautious fall date for finishing the tender-crop harvest in the Grass Valley area is October 26, when there is only a 10 % chance that a light frost has arrived.

The 50 % hard-frost dates are March 9 and December 1; a 50 % chance of a hard frost later than March 9 in spring and a 50 % chance of a hard frost earlier than December 1 in fall gives a clear midpoint for gardeners to gauge extreme-cold risk.

For a cautious spring plan, the light-frost date with only a 10 % chance of frost later is April 30, while the same low-risk principle applies to the fall with October 26. Hard frosts at 28 °F matter more than light frosts at 32 °F because they can damage plant tissue that would survive the milder temperature.

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 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 Grass Valley, CANumbered nearest stations: 1 — Nevada City, CA — 5 mi; 2 — Strawberry Valley, CA — 25 mi; 3 — Tahoe City, CA — 50 mi; 4 — Portola, CA — 52 mi; 5 — near Greenville, CA — 67 mi.NV25 mi · 40 km1. Nevada City, CA — 5 mi12. Strawberry Valley, CA — 25 mi23. Tahoe City, CA — 50 mi34. Portola, CA — 52 mi45. near Greenville, CA — 67 mi5
  1. Nevada City, CA 5 mi (7 km)
  2. Strawberry Valley, CA 25 mi (40 km)
  3. Tahoe City, CA 50 mi (80 km)
  4. Portola, CA 52 mi (84 km)
  5. near Greenville, CA 67 mi (107 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: 39.2042, -121.0681.