Last spring frost
May 9
Frost Dates for Supai, AZ
First fall frost
Oct 19
Growing season
161 days
Hardiness zone
7a
In an average year around Supai, AZ, the last spring frost (32°F) is about May 9 and the first fall frost is about Oct 19, giving roughly a 161-day growing season. To be safe most years, wait until Apr 24 before setting out tender plants.
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%) |
|---|---|---|---|
| Light (36°F) | Jun 6 | May 24 | May 8 |
| Freeze (32°F) | May 27 | May 9 | Apr 24 |
| Hard (28°F) | May 14 | Apr 24 | Apr 6 |
| Severe (24°F) | Apr 27 | Apr 7 | Mar 16 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 6 | Jun 2 | May 31 | May 28 | May 24 | May 20 | May 17 | May 14 | May 8 |
| 32°F | May 27 | May 21 | May 15 | May 12 | May 9 | May 5 | May 2 | Apr 29 | Apr 24 |
| 28°F | May 14 | May 6 | May 1 | Apr 28 | Apr 24 | Apr 21 | Apr 17 | Apr 12 | Apr 6 |
| 24°F | Apr 27 | Apr 20 | Apr 15 | Apr 11 | Apr 7 | Apr 4 | Mar 31 | Mar 23 | Mar 16 |
| 20°F | Apr 11 | Apr 3 | Mar 30 | Mar 23 | Mar 17 | Mar 11 | Mar 6 | Mar 1 | Feb 21 |
| 16°F | Mar 24 | Mar 12 | Mar 5 | Feb 28 | Feb 24 | Feb 18 | Feb 12 | Feb 5 | Jan 28 |
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%) |
|---|---|---|---|
| Light (36°F) | Sep 24 | Oct 6 | Oct 20 |
| Freeze (32°F) | Oct 3 | Oct 19 | Nov 3 |
| Hard (28°F) | Oct 14 | Oct 31 | Nov 13 |
| Severe (24°F) | Oct 23 | Nov 9 | Nov 24 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 24 | Sep 28 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 12 | Oct 16 | Oct 20 |
| 32°F | Oct 3 | Oct 8 | Oct 11 | Oct 15 | Oct 19 | Oct 21 | Oct 24 | Oct 28 | Nov 3 |
| 28°F | Oct 14 | Oct 20 | Oct 24 | Oct 27 | Oct 31 | Nov 3 | Nov 5 | Nov 9 | Nov 13 |
| 24°F | Oct 23 | Oct 30 | Nov 3 | Nov 5 | Nov 9 | Nov 13 | Nov 15 | Nov 19 | Nov 24 |
| 20°F | Nov 1 | Nov 7 | Nov 12 | Nov 16 | Nov 19 | Nov 22 | Nov 26 | Nov 30 | Dec 5 |
| 16°F | Nov 13 | Nov 19 | Nov 23 | Nov 26 | Nov 29 | Dec 2 | Dec 6 | Dec 12 | Dec 18 |
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: Williams 35 Nnw, Az, about 38.2 miles away@if(!empty($station['elevation_ft'])), at 5,990 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
When is the last frost in Supai, AZ?
On average, the last spring frost (32°F) around Supai, AZ is about May 9. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 24.
When is the first frost in the fall?
The first fall frost around Supai, AZ typically arrives about Oct 19. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 9 on average, or Apr 24 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 161 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 86435 Planting calendar → Arizona frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026