Frost dates for Williams Fork Dam, CO
At Williams Fork Dam, the median last spring frost (32°F) is Jun 12 and the median first fall frost is Sep 10, for a typical growing season of 89 days. For a 90% chance that the last frost has passed, wait until Jun 25. Nearby ZIP codes are in USDA hardiness zones 5a to 5b.
- Jun 12Last spring frost (median)50% chance of 32°F after this date
- Jun 25Safer planting date10% chance of 32°F after this date
- Sep 10First fall frost (median)50% chance of 32°F by this date
- 89 daysGrowing season (median)between 32°F freezes
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Jun 16 | Jun 28 | Jul 14 |
| 32°F | May 31 | Jun 12 | Jun 25 |
| 28°F | May 13 | May 26 | Jun 9 |
| 24°F | Apr 28 | May 9 | May 22 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Aug 13 | Aug 29 | Sep 9 |
| 32°F | Aug 31 | Sep 10 | Sep 21 |
| 28°F | Sep 8 | Sep 20 | Oct 3 |
| 24°F | Sep 19 | Oct 1 | Oct 16 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 37 days | 59 days | 78 days |
| 32°F | 71 days | 89 days | 105 days |
| 28°F | 97 days | 115 days | 134 days |
| 24°F | 127 days | 144 days | 160 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 80451 | 5b | -15 to -10°F | 14 km |
| 80468 | 5a | -20 to -15°F | 16 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00059096, at 40.0375, -106.2039, elevation 2322 m (7,618 ft).
- Data quality: Representative (10+ years), 26 years of freeze data.
- Average days per year at or below 32°F: 242.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Kremmling (14 km)
- Green Mount Dam (21 km)
- Grand Lake 6 SSW (33 km)
- Fraser (35 km)
- Grand Lake 1 NW (41 km)
- Vail (46 km)
- Dillon 1 E (48 km)
- Spicer (53 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.