U.S. Frost Dates by Weather Station

NOAA station USC00357169 · Oregon

Frost Dates for Riddle, OR

NOAA weather station Riddle (USC00357169), Oregon · elevation 680 ft (207 m) · hardiness zone 9a*

  • Lower-risk planting dateafter April 27only 1 spring in 10 still has a frost later
  • Typical last frostMarch 3150% chance of a frost after it
  • Typical first fall frostNovember 650% chance of a frost before it
  • Frost-free season221 daystypical year, 32°F
  • Hardiness zone9acalculated*

The year at a glance

Frost season at Riddle, ORSpring: a frost after February 27 in 9 years out of 10, after March 31 in half of the years, after April 27 in 1 year out of 10. Fall: the first frost comes before October 11 in 1 year out of 10, before November 6 in half of the years, before December 13 in 9 years out of 10. Typical frost-free season: 221 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Mar 31First frost ~Nov 6Frost season at Riddle, ORSpring: a frost after February 27 in 9 years out of 10, after March 31 in half of the years, after April 27 in 1 year out of 10. Fall: the first frost comes before October 11 in 1 year out of 10, before November 6 in half of the years, before December 13 in 9 years out of 10. Typical frost-free season: 221 days.JFMAMJJASONDLast frost ~Mar 31First frost ~Nov 6
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 27October 11
50% (typical)March 31November 6
90% (likely)February 27December 13
Frost-free season (32°F, 50% chance)
221 days
Hard frost (28°F), last in spring, 50% chance after
February 20
Hard frost (28°F), first in fall, 50% chance before
December 10

The last 15 years (2006–2020 normals)

Typical last frost April 3 (3 days later than the 30-year normal), typical first fall frost November 6. Frost-free season 219 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 Riddle: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 27, 20% April 18, 30% April 11, 40% April 5, 50% March 31, 60% March 26, 70% March 20, 80% March 10, 90% February 27. Observed last spring frost in recent years: 2021 April 27, 2022 April 15, 2023 April 18, 2024 April 22, 2025 April 15, 2026 April 17.Spring: last frostChance of a frost after this date10%50%90%Mar 1Apr 1May 1Apr 27Mar 31Feb 272021: April 272022: April 152023: April 182024: April 222025: April 152026: April 17Fall at Riddle: chance of a frost before this dateFall, chance of a frost before the date: 10% October 11, 20% October 20, 30% October 26, 40% October 31, 50% November 6, 60% November 15, 70% November 25, 80% December 4, 90% December 13. Observed first fall frost in recent years: 2021 November 22, 2022 November 15, 2023 October 29, 2024 November 29, 2025 December 14.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Dec 1Oct 11Nov 6Dec 132021: November 222022: November 152023: October 292024: November 292025: December 14
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 27November 22
2022April 15November 15
2023April 18October 29
2024April 22November 29
2025April 15December 14
2026April 17season not over yet

What these dates mean

October 11 marks the cautious fall date in Riddle for finishing the harvest; there is only a 10 % chance that a light frost has arrived earlier, making it the preferred deadline for tender crops. In spring the cautious date for setting out tender crops is April 27, when the chance of a light frost later than that day is also 10 %. The 50 % light-frost dates are March 31 in spring and November 6 in fall, meaning there is an even odds of a frost occurring after the March 31 date or before the November 6 date. The median hard-frost dates are February 20 for spring and December 10 for fall; a hard frost at 28 °F can damage tender plants more severely than the 32 °F light frost. The record covers 26 years, and the span between the two 32 °F 50 % dates is 221 days.

How to read the probabilities

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

  • Spring: "10% after April 27" 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 11" 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 Riddle, ORNumbered nearest stations: 1 — near Roseburg, OR — 18 mi; 2 — Sexton Summit, OR — 24 mi; 3 — near Shady Cove, OR — 40 mi; 4 — Prospect, OR — 45 mi; 5 — near Coquille, OR — 46 mi.25 mi · 40 km1. near Roseburg, OR — 18 mi12. Sexton Summit, OR — 24 mi23. near Shady Cove, OR — 40 mi34. Prospect, OR — 45 mi45. near Coquille, OR — 46 mi5
  1. near Roseburg, OR 18 mi (29 km)
  2. Sexton Summit, OR 24 mi (39 km)
  3. near Shady Cove, OR 40 mi (64 km)
  4. Prospect, OR 45 mi (73 km)
  5. near Coquille, OR 46 mi (74 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: 42.9508, -123.3572.