U.S. Frost Dates by Weather Station

NOAA station USC00356907 · Oregon

Frost Dates for Prospect, OR

NOAA weather station Prospect 2 SW (USC00356907), Oregon · elevation 2482 ft (757 m) · hardiness zone 8a*

  • Lower-risk planting dateafter June 9only 1 spring in 10 still has a frost later
  • Typical last frostMay 1950% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season136 daystypical year, 32°F
  • Hardiness zone8acalculated*

The year at a glance

Frost season at Prospect, ORSpring: a frost after April 29 in 9 years out of 10, after May 19 in half of the years, after June 9 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before October 3 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 136 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 19First frost ~Oct 3Frost season at Prospect, ORSpring: a frost after April 29 in 9 years out of 10, after May 19 in half of the years, after June 9 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before October 3 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 136 days.JFMAMJJASONDLast frost ~May 19First frost ~Oct 3
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 9September 13
50% (typical)May 19October 3
90% (likely)April 29October 20
Frost-free season (32°F, 50% chance)
136 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost May 17 (2 days earlier than the 30-year normal), typical first fall frost October 5 (2 days later). Frost-free season 141 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 Prospect: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 9, 20% June 1, 30% May 28, 40% May 23, 50% May 19, 60% May 15, 70% May 11, 80% May 6, 90% April 29.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 9May 19Apr 29Fall at Prospect: chance of a frost before this dateFall, chance of a frost before the date: 10% September 13, 20% September 19, 30% September 26, 40% September 30, 50% October 3, 60% October 6, 70% October 10, 80% October 15, 90% October 20.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Nov 1Sep 13Oct 3Oct 20
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.

What these dates mean

The 136 days between the 50% dates in Prospect, Oregon, define the central window for planting and harvesting tender crops. The 50% date is May 19, giving even odds for a light frost later in spring, and the 50% date is October 3, giving even odds for a light frost earlier in fall. For a cautious approach, gardeners would wait until the June 9 date, which carries only a 10% chance of a frost later, before setting out tender crops in spring, and aim to finish tender harvest by the September 13 date, which carries only a 10% chance of a frost earlier in fall.

Hard frosts at 28 °F, whose 50% dates are April 26 and October 24, are more damaging than the 32 °F light frosts because they can injure plants that would otherwise survive a milder chill.

How to read the probabilities

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

  • Spring: "10% after June 9" 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 September 13" 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 Prospect, ORNumbered nearest stations: 1 — near Shady Cove, OR — 9 mi; 2 — near Medford, OR — 30 mi; 3 — Toketee Falls, OR — 38 mi; 4 — Sexton Summit, OR — 44 mi; 5 — Riddle, OR — 45 mi.OR25 mi · 40 km1. near Shady Cove, OR — 9 mi12. near Medford, OR — 30 mi23. Toketee Falls, OR — 38 mi34. Sexton Summit, OR — 44 mi45. Riddle, OR — 45 mi5
  1. near Shady Cove, OR 9 mi (15 km)
  2. near Medford, OR 30 mi (49 km)
  3. Toketee Falls, OR 38 mi (60 km)
  4. Sexton Summit, OR 44 mi (71 km)
  5. Riddle, OR 45 mi (73 km)

Sources

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

Station coordinates: 42.7342, -122.5164.