U.S. Frost Dates by Weather Station

NOAA station USW00023062 · Colorado

Frost Dates near Aurora, CO

NOAA weather station Denver-Stapleton (USW00023062), Colorado · elevation 5286 ft (1611 m) · hardiness zone 6a*

Aurora is the nearest town to the station (3.0 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 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 450% chance of a frost after it
  • Typical first fall frostOctober 850% chance of a frost before it
  • Frost-free season156 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season near Aurora, COSpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 8 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 156 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 4First frost ~Oct 8Frost season near Aurora, COSpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 8 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 156 days.JFMAMJJASONDLast frost ~May 4First frost ~Oct 8
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 16September 25
50% (typical)May 4October 8
90% (likely)April 20October 20
Frost-free season (32°F, 50% chance)
156 days
Hard frost (28°F), last in spring, 50% chance after
April 22
Hard frost (28°F), first in fall, 50% chance before
October 18

The last 15 years (2006–2020 normals)

Typical last frost May 2 (2 days earlier than the 30-year normal), typical first fall frost October 13 (5 days later). Frost-free season 161 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 Aurora: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 11, 30% May 8, 40% May 6, 50% May 4, 60% May 2, 70% April 29, 80% April 24, 90% April 20. Observed last spring frost in recent years: 2021 May 12, 2022 May 22, 2023 April 24, 2024 April 28, 2025 April 20, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 4Apr 202021: May 122022: May 222023: April 242024: April 282025: April 202026: May 19Fall near Aurora: chance of a frost before this dateFall, chance of a frost before the date: 10% September 25, 20% September 30, 30% October 3, 40% October 6, 50% October 8, 60% October 11, 70% October 14, 80% October 17, 90% October 20. Observed first fall frost in recent years: 2021 October 15, 2022 October 17, 2023 October 13, 2024 October 31, 2025 October 19.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 25Oct 8Oct 202021: October 152022: October 172023: October 132024: October 312025: October 19
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 12October 15
2022May 22October 17
2023April 24October 13
2024April 28October 31
2025April 20October 19
2026May 19season not over yet

What these dates mean

The 156 days between the 32°F 50% dates in the Aurora area frame the period when a light frost is as likely to have occurred as not, running from May 4 to October 8. Within that window gardeners can expect the bulk of the growing season, while the hard-frost 28°F median dates of April 22 and October 18 sit just inside the edges of the riskier period.

For a cautious spring plan the 10% chance date is May 16, meaning only a small chance of a light frost later, while planting on April 20 carries a 90% chance and is a gamble. In the fall the cautious date is September 25, when there is only a 10% chance a light frost has arrived; aiming for October 20 would involve a 90% chance of an early frost.

A hard frost at 28°F matters more than a light frost at 32°F because the lower temperature can injure or kill plants that would otherwise survive a milder freeze.

How to read the probabilities

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

  • Spring: "10% after May 16" 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 25" 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 Aurora, CONumbered nearest stations: 1 — Northglenn, CO — 12 mi; 2 — Brighton, CO — 13 mi; 3 — Wheat Ridge, CO — 13 mi; 4 — Castle Rock, CO — 24 mi; 5 — Evergreen, CO — 25 mi.25 mi · 40 km1. Northglenn, CO — 12 mi12. Brighton, CO — 13 mi23. Wheat Ridge, CO — 13 mi34. Castle Rock, CO — 24 mi45. Evergreen, CO — 25 mi5
  1. Northglenn, CO 12 mi (19 km)
  2. Brighton, CO 13 mi (20 km)
  3. Wheat Ridge, CO 13 mi (21 km)
  4. Castle Rock, CO 24 mi (39 km)
  5. Evergreen, CO 25 mi (41 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: 39.7633, -104.8694.