U.S. Frost Dates by Weather Station

NOAA station USC00051886 · Colorado

Frost Dates for Cortez, CO

NOAA weather station Cortez (USC00051886), Colorado · elevation 6167 ft (1880 m) · hardiness zone 6a*

  • 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 750% chance of a frost before it
  • Frost-free season147 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Cortez, COSpring: a frost after April 30 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 26 in 1 year out of 10, before October 7 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 147 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Oct 7Frost season at Cortez, COSpring: a frost after April 30 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 26 in 1 year out of 10, before October 7 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 147 days.JFMAMJJASONDLast frost ~May 12First frost ~Oct 7
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 31September 26
50% (typical)May 12October 7
90% (likely)April 30October 21
Frost-free season (32°F, 50% chance)
147 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 17

The last 15 years (2006–2020 normals)

Typical last frost May 12 (same as the 30-year normal), typical first fall frost October 6 (1 day earlier). Frost-free season 146 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 Cortez: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 31, 20% May 23, 30% May 19, 40% May 15, 50% May 12, 60% May 9, 70% May 6, 80% May 3, 90% April 30. Observed last spring frost in recent years: 2021 May 24, 2022 May 30, 2023 April 29, 2024 May 22, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 31May 12Apr 302021: May 242022: May 302023: April 292024: May 222026: May 7Fall at Cortez: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% September 30, 30% October 3, 40% October 5, 50% October 7, 60% October 10, 70% October 13, 80% October 16, 90% October 21. Observed first fall frost in recent years: 2021 October 14, 2022 October 24, 2023 October 13, 2024 October 30, 2025 October 17.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 7Oct 212021: October 142022: October 242023: October 132024: October 302025: October 17
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
2021May 24October 14
2022May 30October 24
2023April 29October 13
2024May 22October 30
2025incomplete recordOctober 17
2026May 7season not over yet

What these dates mean

September 26 is the cautious fall date in Cortez for finishing the harvest, carrying only a 10 % chance that a light frost has arrived earlier.

In spring the cautious date for setting out tender crops is May 31, when the chance of a light frost later than that day is just 10 %; the earlier April 30 date represents a 90 % gamble. The 50 % dates—May 12 for spring and October 7 for fall—each mark the point at which a light frost is as likely to occur later (spring) or earlier (fall) as not, giving gardeners a midpoint reference for planning.

Hard-frost thresholds are lower, with the 50 % hard-frost dates on April 30 and October 17; a 28 °F frost can damage or kill plants that survive a 32 °F light frost, so it is a more critical limit for tender 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 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 Cortez, CONumbered nearest stations: 1 — Farmington, NM — 48 mi; 2 — Blanding, UT — 52 mi; 3 — Bluff, UT — 53 mi; 4 — Natural Bridges National Monument, UT — 78 mi; 5 — Canyonlands-The Needles, UT — 85 mi.COAZ50 mi · 80 km1. Farmington, NM — 48 mi12. Blanding, UT — 52 mi23. Bluff, UT — 53 mi34. Natural Bridges National Monument, UT — 78 mi45. Canyonlands-The Needles, UT — 85 mi5
  1. Farmington, NM 48 mi (77 km)
  2. Blanding, UT 52 mi (84 km)
  3. Bluff, UT 53 mi (85 km)
  4. Natural Bridges National Monument, UT 78 mi (125 km)
  5. Canyonlands-The Needles, UT 85 mi (137 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 37.3444, -108.595.