U.S. Frost Dates by Weather Station

NOAA station USC00355734 · Oregon

Frost Dates for Moro, OR

NOAA weather station Moro (USC00355734), Oregon · elevation 1870 ft (570 m) · hardiness zone 7a*

  • Lower-risk planting dateafter May 31only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season at Moro, ORSpring: a frost after April 27 in 9 years out of 10, after May 12 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before October 4 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Oct 4Frost season at Moro, ORSpring: a frost after April 27 in 9 years out of 10, after May 12 in half of the years, after May 31 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before October 4 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 143 days.JFMAMJJASONDLast frost ~May 12First frost ~Oct 4
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.Today

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)May 31September 16
50% (typical)May 12October 4
90% (likely)April 27October 18
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost May 14 (2 days later than the 30-year normal), typical first fall frost October 3 (1 day earlier). Frost-free season 143 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 Moro: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 31, 20% May 24, 30% May 20, 40% May 15, 50% May 12, 60% May 8, 70% May 5, 80% May 1, 90% April 27. Observed last spring frost in recent years: 2021 April 25, 2022 May 13, 2023 April 25.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 31May 12Apr 272021: April 252022: May 132023: April 25Fall at Moro: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 24, 30% September 28, 40% October 1, 50% October 4, 60% October 6, 70% October 9, 80% October 13, 90% October 18. Observed first fall frost in recent years: 2021 October 6, 2022 November 2, 2023 October 28.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 16Oct 4Oct 182021: October 62022: November 22023: October 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 25October 6
2022May 13November 2
2023April 25October 28
2024incomplete recordincomplete record
2025no datano data
2026no dataseason not over yet

What these dates mean

May 31 is the cautious spring date for light frost in Moro, and it marks the point when a gardener can set out tender crops with only a 10 % chance of a later frost. The 50% dates are May 12 and October 4; each represents an even-odds moment for a frost to occur, helping the gardener gauge risk around the middle of the season. The 28 °F 50% dates are April 26 in spring and October 16 in fall, indicating when a hard frost is as likely as not.

In fall, September 16 serves as the cautious date for finishing harvest of tender crops, carrying just a 10 % chance that a frost has already arrived. A hard frost at 28 °F can injure plant tissue that would normally survive a light frost at 32 °F, so it represents a greater threat to crops.

How to read the probabilities

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

  • Spring: "10% after May 31" 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 16" 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 Moro, ORNumbered nearest stations: 1 — near Dallesport, WA — 23 mi; 2 — Government Camp, OR — 51 mi; 3 — Boardman, OR — 56 mi; 4 — Heppner, OR — 57 mi; 5 — near Warm Springs, OR — 58 mi.ORWA25 mi · 40 km1. near Dallesport, WA — 23 mi12. Government Camp, OR — 51 mi23. Boardman, OR — 56 mi34. Heppner, OR — 57 mi45. near Warm Springs, OR — 58 mi5
  1. near Dallesport, WA 23 mi (38 km)
  2. Government Camp, OR 51 mi (82 km)
  3. Boardman, OR 56 mi (90 km)
  4. Heppner, OR 57 mi (91 km)
  5. near Warm Springs, OR 58 mi (94 km)

Sources

* Hardiness zone 7a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 45.4825, -120.7236.