Frost dates for Mountain Dell Dam, UT
At Mountain Dell Dam, the median last spring frost (32°F) is May 7 and the median first fall frost is Oct 14, for a typical growing season of 158 days. For a 90% chance that the last frost has passed, wait until May 27. Nearby ZIP codes are in USDA hardiness zone 6b.
- May 7Last spring frost (median)50% chance of 32°F after this date
- May 27Safer planting date10% chance of 32°F after this date
- Oct 14First fall frost (median)50% chance of 32°F by this date
- 158 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 | May 8 | May 25 | Jun 11 |
| 32°F | Apr 21 | May 7 | May 27 |
| 28°F | Apr 4 | Apr 21 | May 6 |
| 24°F | Mar 14 | Apr 5 | Apr 21 |
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 | Sep 15 | Oct 1 | Oct 15 |
| 32°F | Sep 29 | Oct 14 | Oct 27 |
| 28°F | Oct 11 | Oct 26 | Nov 9 |
| 24°F | Oct 22 | Nov 6 | Nov 21 |
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 | 104 days | 128 days | 150 days |
| 32°F | 133 days | 158 days | 180 days |
| 28°F | 166 days | 188 days | 209 days |
| 24°F | 193 days | 213 days | 237 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 |
|---|---|---|---|
| 84109 | 6b | -5 to 0°F | 5 km |
| 84108 | 6b | -5 to 0°F | 7 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 USC00425892, at 40.7486, -111.7233, elevation 1652 m (5,420 ft).
- Data quality: Representative (10+ years), 19 years of freeze data.
- Average days per year at or below 32°F: 158.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Salt Lake City E Bench (8 km)
- City Creek Water Plant (12 km)
- Salt Lake Triad Center (15 km)
- Cottonwood Weir (15 km)
- Bountiful-Val Verda (18 km)
- Alta (19 km)
- Bountiful Bench (19 km)
- Silver Lake Brighton (20 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.