Frost dates for Longmont 2 ESE, CO
At Longmont 2 ESE, the median last spring frost (32°F) is May 7 and the median first fall frost is Oct 5, for a typical growing season of 151 days. For a 90% chance that the last frost has passed, wait until May 22. Nearby ZIP codes are in USDA hardiness zones 5b to 6a.
- May 7Last spring frost (median)50% chance of 32°F after this date
- May 22Safer planting date10% chance of 32°F after this date
- Oct 5First fall frost (median)50% chance of 32°F by this date
- 151 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 5 | May 18 | Jun 2 |
| 32°F | Apr 24 | May 7 | May 22 |
| 28°F | Apr 11 | Apr 28 | May 12 |
| 24°F | Mar 29 | Apr 14 | May 1 |
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 14 | Sep 28 | Oct 8 |
| 32°F | Sep 23 | Oct 5 | Oct 16 |
| 28°F | Sep 30 | Oct 12 | Oct 25 |
| 24°F | Oct 6 | Oct 21 | Nov 5 |
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 | 111 days | 132 days | 151 days |
| 32°F | 131 days | 151 days | 169 days |
| 28°F | 151 days | 169 days | 189 days |
| 24°F | 167 days | 189 days | 212 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 |
|---|---|---|---|
| 80501 | 5b | -15 to -10°F | 2 km |
| 80504 | 5b | -15 to -10°F | 4 km |
| 80542 | 5b | -15 to -10°F | 10 km |
| 80503 | 6a | -10 to -5°F | 11 km |
| 80520 | 5b | -15 to -10°F | 14 km |
| 80516 | 5b | -15 to -10°F | 14 km |
| 80513 | 5b | -15 to -10°F | 15 km |
| 80514 | 5b | -15 to -10°F | 15 km |
| 80530 | 5b | -15 to -10°F | 15 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 USC00055116, at 40.1694, -105.0775, elevation 1509 m (4,950 ft).
- Data quality: Representative (10+ years), 17 years of freeze data.
- Average days per year at or below 32°F: 178.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Boulder (25 km)
- Loveland 2n (30 km)
- Northglenn (31 km)
- Waterdale (31 km)
- Brighton 3 SE (32 km)
- Gross Rsvr (35 km)
- Allenspark 3nw (38 km)
- Ralston Rsvr (40 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.