U.S. Frost Dates by Weather Station

NOAA station USC00049026 · California

Frost Dates near Lewiston, CA

NOAA weather station Trinity River Hatchery (USC00049026), California · elevation 1861 ft (567 m) · hardiness zone 8b*

Lewiston is the nearest town to the station (1.5 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 May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2350% chance of a frost after it
  • Typical first fall frostOctober 2250% chance of a frost before it
  • Frost-free season178 daystypical year, 32°F
  • Hardiness zone8bcalculated*

The year at a glance

Frost season near Lewiston, CASpring: a frost after April 3 in 9 years out of 10, after April 23 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before October 4 in 1 year out of 10, before October 22 in half of the years, before November 13 in 9 years out of 10. Typical frost-free season: 178 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 23First frost ~Oct 22Frost season near Lewiston, CASpring: a frost after April 3 in 9 years out of 10, after April 23 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before October 4 in 1 year out of 10, before October 22 in half of the years, before November 13 in 9 years out of 10. Typical frost-free season: 178 days.JFMAMJJASONDLast frost ~Apr 23First frost ~Oct 22
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 11October 4
50% (typical)April 23October 22
90% (likely)April 3November 13
Frost-free season (32°F, 50% chance)
178 days
Hard frost (28°F), last in spring, 50% chance after
March 28
Hard frost (28°F), first in fall, 50% chance before
November 6

The last 15 years (2006–2020 normals)

Typical last frost April 23 (same as the 30-year normal), typical first fall frost October 19 (3 days earlier). Frost-free season 179 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 Lewiston: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 4, 30% April 30, 40% April 26, 50% April 23, 60% April 19, 70% April 15, 80% April 10, 90% April 3. Observed last spring frost in recent years: 2021 April 1, 2022 May 3, 2023 April 20, 2024 April 7, 2025 March 19.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 23Apr 32021: April 12022: May 32023: April 202024: April 72025: March 19Fall near Lewiston: chance of a frost before this dateFall, chance of a frost before the date: 10% October 4, 20% October 9, 30% October 14, 40% October 18, 50% October 22, 60% October 25, 70% October 29, 80% November 2, 90% November 13. Observed first fall frost in recent years: 2021 October 12, 2022 October 23, 2023 October 26, 2024 October 18, 2025 December 3.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Dec 1Oct 4Oct 22Nov 132021: October 122022: October 232023: October 262024: October 182025: December 3
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 1October 12
2022May 3October 23
2023April 20October 26
2024April 7October 18
2025March 19December 3
2026incomplete recordseason not over yet

What these dates mean

October 4 is the cautious fall date for finishing the harvest of tender crops in the Lewiston area, carrying only a 10 % chance that a light frost has arrived earlier.

For a gardener, the 50 % date for a light frost is April 23, indicating an even chance of a frost at 32 °F later, and the 50 % date for a light frost later in the year is October 22, indicating an even chance of a frost earlier. The 50 % date for a hard frost is March 28, and the 50 % date for a hard frost in fall is November 6, each marking the point where a frost at 28 °F is equally likely to have occurred or not.

A cautious planting schedule uses the May 11 date, which has a 10 % chance of a light frost later, for setting out tender crops in spring, and the October 4 date for ending their harvest in fall. Because a hard frost at 28 °F can damage plants that survive a light frost at 32 °F, it is a more critical threshold for winter protection.

How to read the probabilities

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

  • Spring: "10% after May 11" 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 4" 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 Lewiston, CANumbered nearest stations: 1 — Redding, CA — 30 mi; 2 — near Dunsmuir, CA — 41 mi; 3 — Chester, CA — 87 mi; 4 — near Redwood Valley, CA — 96 mi; 5 — near Greenville, CA — 98 mi.CA50 mi · 80 km1. Redding, CA — 30 mi12. near Dunsmuir, CA — 41 mi23. Chester, CA — 87 mi34. near Redwood Valley, CA — 96 mi45. near Greenville, CA — 98 mi5
  1. Redding, CA 30 mi (48 km)
  2. near Dunsmuir, CA 41 mi (67 km)
  3. Chester, CA 87 mi (139 km)
  4. near Redwood Valley, CA 96 mi (154 km)
  5. near Greenville, CA 98 mi (157 km)

Sources

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

Station coordinates: 40.7264, -122.7947.