Growing season
72 days
Frost Dates for Tonsina, AK
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) | Jun 9 | May 24 | May 11 |
| Severe (24°F) | May 22 | May 8 | Apr 28 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Jun 9 | Jun 3 | May 31 | May 27 | May 24 | May 21 | May 18 | May 14 | May 11 |
| 24°F | May 22 | May 16 | May 12 | May 10 | May 8 | May 6 | May 3 | May 1 | Apr 28 |
| 20°F | May 7 | May 4 | May 1 | Apr 29 | Apr 26 | Apr 24 | Apr 21 | Apr 18 | Apr 13 |
| 16°F | Apr 30 | Apr 26 | Apr 22 | Apr 19 | Apr 16 | Apr 14 | Apr 11 | Apr 9 | Apr 6 |
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 23 | Sep 5 | Sep 20 |
| Severe (24°F) | Sep 3 | Sep 18 | Sep 30 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Aug 23 | Aug 30 | Sep 1 | Sep 3 | Sep 5 | Sep 9 | Sep 12 | Sep 16 | Sep 20 |
| 24°F | Sep 3 | Sep 8 | Sep 12 | Sep 15 | Sep 18 | Sep 21 | Sep 24 | Sep 27 | Sep 30 |
| 20°F | Sep 14 | Sep 18 | Sep 23 | Sep 27 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 12 |
| 16°F | Sep 21 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 8 | Oct 11 | Oct 15 | Oct 19 |
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: Tonsina, Ak, about 17.4 miles away@if(!empty($station['elevation_ft'])), at 1,579 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 72 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 99573 Planting calendar → Alaska frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026