U.S. Frost Dates by Weather Station

NOAA station USC00051681 · Colorado

Frost Dates near Coal Creek, CO

NOAA weather station Coal Creek Canyon (USC00051681), Colorado · elevation 8950 ft (2728 m) · hardiness zone 5b*

Coal Creek is the nearest town to the station (0.8 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 June 19only 1 spring in 10 still has a frost later
  • Typical last frostJune 550% chance of a frost after it
  • Typical first fall frostSeptember 1650% chance of a frost before it
  • Frost-free season103 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season near Coal Creek, COSpring: a frost after May 23 in 9 years out of 10, after June 5 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before September 2 in 1 year out of 10, before September 16 in half of the years, before September 28 in 9 years out of 10. Typical frost-free season: 103 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 5First frost ~Sep 16Frost season near Coal Creek, COSpring: a frost after May 23 in 9 years out of 10, after June 5 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before September 2 in 1 year out of 10, before September 16 in half of the years, before September 28 in 9 years out of 10. Typical frost-free season: 103 days.JFMAMJJASONDLast frost ~Jun 5First frost ~Sep 16
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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 19September 2
50% (typical)June 5September 16
90% (likely)May 23September 28
Frost-free season (32°F, 50% chance)
103 days
Hard frost (28°F), last in spring, 50% chance after
May 21
Hard frost (28°F), first in fall, 50% chance before
September 26

The last 15 years (2006–2020 normals)

Typical last frost June 2 (3 days earlier than the 30-year normal), typical first fall frost September 17 (1 day later). Frost-free season 104 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 Coal Creek: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 19, 20% June 14, 30% June 11, 40% June 7, 50% June 5, 60% June 2, 70% May 31, 80% May 28, 90% May 23.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jun 19Jun 5May 23Fall near Coal Creek: chance of a frost before this dateFall, chance of a frost before the date: 10% September 2, 20% September 7, 30% September 10, 40% September 13, 50% September 16, 60% September 19, 70% September 22, 80% September 24, 90% September 28.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 2Sep 16Sep 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.

What these dates mean

June 19 is the cautious spring date in the Coal Creek area and it allows a gardener to set out tender crops when the chance of a light frost later than this date is only ten percent. The median date for light frost in spring is June 5; a 50 % chance of a frost later than that day simply marks the point where risk is even. In fall the cautious date is September 2, giving a ten percent chance that a light frost has already arrived and signalling when tender crops should be finished. The median fall date for light frost is September 16, again an even-odds point.

The 50 % dates for hard frost are May 21 in spring and September 26 in fall; a hard frost at 28 °F can damage plants that survive a light frost, so it represents a more severe risk. These dates summarize the 25-year record for the station.

How to read the probabilities

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

  • Spring: "10% after June 19" 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 2" 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 Coal Creek, CONumbered nearest stations: 1 — Boulder, CO — 9 mi; 2 — Wheat Ridge, CO — 16 mi; 3 — Evergreen, CO — 18 mi; 4 — Northglenn, CO — 20 mi; 5 — Georgetown, CO — 21 mi.25 mi · 40 km1. Boulder, CO — 9 mi12. Wheat Ridge, CO — 16 mi23. Evergreen, CO — 18 mi34. Northglenn, CO — 20 mi45. Georgetown, CO — 21 mi5
  1. Boulder, CO 9 mi (15 km)
  2. Wheat Ridge, CO 16 mi (27 km)
  3. Evergreen, CO 18 mi (29 km)
  4. Northglenn, CO 20 mi (32 km)
  5. Georgetown, CO 21 mi (34 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 39.8958, -105.3847.