Growing season
43 days
Frost Dates for Boulder, WY
Hardiness zone
4a
Frost normals for this location are limited (the nearest long-term weather station may not report all thresholds). The available data is shown below.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Hard (28°F) | Jul 5 | Jun 14 | May 30 |
| Severe (24°F) | Jun 17 | May 28 | May 13 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Jul 5 | Jun 29 | Jun 24 | Jun 18 | Jun 14 | Jun 11 | Jun 7 | Jun 3 | May 30 |
| 24°F | Jun 17 | Jun 8 | Jun 4 | Jun 1 | May 28 | May 25 | May 22 | May 18 | May 13 |
| 20°F | May 31 | May 25 | May 21 | May 18 | May 15 | May 12 | May 9 | May 6 | May 1 |
| 16°F | May 17 | May 11 | May 8 | May 4 | May 2 | Apr 30 | Apr 27 | Apr 23 | Apr 17 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Hard (28°F) | Aug 15 | Aug 31 | Sep 13 |
| Severe (24°F) | Aug 30 | Sep 13 | Sep 26 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Aug 15 | Aug 20 | Aug 24 | Aug 28 | Aug 31 | Sep 2 | Sep 5 | Sep 8 | Sep 13 |
| 24°F | Aug 30 | Sep 3 | Sep 6 | Sep 9 | Sep 13 | Sep 16 | Sep 19 | Sep 22 | Sep 26 |
| 20°F | Sep 12 | Sep 17 | Sep 21 | Sep 24 | Sep 27 | Sep 30 | Oct 2 | Oct 6 | Oct 10 |
| 16°F | Sep 25 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 22 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Boulder Rearing Stn, Wy, about 16 miles away@if(!empty($station['elevation_ft'])), at 6,940 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 43 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 82923 Planting calendar → Wyoming frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026