USDA Hardiness Zone 8a
Frost Dates for 85534 — Duncan, Arizona
NOAA 1991–2020 normals from Duncan, AZ (3,660 ft), 1 miles north.
Updated
In Duncan, the last spring frost (32°F) is around April 24 in half of years and has passed by May 8 in nine years out of ten. The first fall frost comes around October 25, as early as October 11 one year in ten, leaving a typical freeze-free season of 183 days (NOAA, Duncan, AZ).
- Last spring frost
- April 24
- First fall frost
- October 25
- Growing season
- 183 days
- Hardiness zone
- 8a
50% probability
50% probability
freeze-free, 50%
10 to 15°F (-12.2 to -9.4°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 45%
- Snow per year
- 1"
median, 1991–2020
median, 1991–2020
9 of 20 observed
NOAA normal
Frost risk by date in Duncan
Half of springs at Duncan, AZ see their last 32°F night by April 24; only one in ten is past it by April 8, and one in ten still has one after May 8. Planting tender crops after April 30 leaves a 30% risk of a frost on them, after May 3 20%, and after May 8 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 95% of the 98 Arizona stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 25 in half of years, as early as October 11 one year in ten, and holds off past November 5 one year in ten. A hard freeze of 28°F follows 8 days later, around November 2; in spring the one-in-ten date for 28°F is April 27, 11 days before the 32°F one. The freeze-free season lasts 183 days in a typical year, shorter than at 74% of the 98 Arizona stations; it reaches 203 days one year in ten and falls short of 162 one year in ten. On average 113 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 11 days longer, to about May 5, and return around October 17. Severe cold of 16°F or below comes in 99% of winters, usually between December 3 and February 6.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 22 | Apr 27 | Apr 30 | May 2 | May 5 | May 7 | May 10 | May 14 | May 18 |
| 32°F | Apr 8 | Apr 13 | Apr 18 | Apr 21 | Apr 24 | Apr 27 | Apr 30 | May 3 | May 8 |
| 28°F | Mar 16 | Mar 24 | Mar 30 | Apr 3 | Apr 7 | Apr 10 | Apr 14 | Apr 20 | Apr 27 |
| 24°F | Feb 26 | Mar 3 | Mar 7 | Mar 12 | Mar 15 | Mar 20 | Mar 27 | Apr 1 | Apr 7 |
| 20°F | Feb 1 | Feb 10 | Feb 16 | Feb 22 | Feb 27 | Mar 1 | Mar 5 | Mar 9 | Mar 15 |
| 16°F99% of yrs | Jan 5 | Jan 20 | Jan 28 | Feb 2 | Feb 6 | Feb 12 | Feb 18 | Feb 25 | Mar 3 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 4 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 19 | Oct 21 | Oct 25 | Oct 29 |
| 32°F | Oct 11 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 1 | Nov 5 |
| 28°F | Oct 20 | Oct 24 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 15 |
| 24°F | Oct 27 | Nov 1 | Nov 5 | Nov 8 | Nov 12 | Nov 15 | Nov 18 | Nov 21 | Nov 26 |
| 20°F | Nov 4 | Nov 10 | Nov 15 | Nov 18 | Nov 21 | Nov 24 | Nov 27 | Dec 1 | Dec 7 |
| 16°F99% of yrs | Nov 15 | Nov 22 | Nov 26 | Nov 30 | Dec 3 | Dec 7 | Dec 12 | Dec 18 | Jan 1 |
Freeze probabilities 1991–2020 at Duncan, AZ, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 85534 →Compare Duncan with another place →
Weather by month in Duncan
July is the warmest month at Duncan, AZ, averaging 98°F by day and 66°F at night; December is the coldest at 59°F and 25°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 29% of years.
Warmth for growing adds up to 4,911 growing degree days a year (base 50°F), fewer than at 64% of the 102 Arizona stations. 37% of them (1,831) have built up by the end of June, and July adds the most, 977. Precipitation totals 10.4 inches a year, most in August (2.2") and least in April (0.2"); May to September bring 55% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 60 | 25 | 0.9 | 100% | 25 | 6 |
| Feb | 65 | 29 | 0.8 | 100% | 20 | 25 |
| Mar | 73 | 33 | 0.5 | 100% | 15 | 122 |
| Apr | 81 | 39 | 0.2 | 96% | 7 | 291 |
| May | 89 | 47 | 0.3 | 29% | 1 | 558 |
| Jun | 98 | 57 | 0.3 | 0% | 0 | 829 |
| Jul | 98 | 66 | 1.7 | 0% | 0 | 977 |
| Aug | 96 | 65 | 2.2 | 0% | 0 | 932 |
| Sep | 91 | 56 | 1.2 | 0% | 0 | 707 |
| Oct | 81 | 43 | 0.7 | 73% | 3 | 379 |
| Nov | 69 | 31 | 0.6 | 100% | 18 | 81 |
| Dec | 59 | 25 | 1.0 | 100% | 25 | 5 |
Monthly normals 1991–2020 at Duncan, AZ (3,660 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Clifton, AZ, 25 miles northwest of Duncan, has a last frost 57 days earlier (February 26), a first frost 29 days later (November 23), a season 85 days longer.
When it snows in Duncan, Arizona
Measurable snow is rare here: only 9 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Redrock 1 NNE, NM, 22.6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85534
| When | What to do |
|---|---|
| February 13 – February 27 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 27 – March 13 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 27 – April 10 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 24 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 2 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 11 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 25 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 85534 is 1 mile from Duncan, AZ, which stands at 3,660 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 85534 in zone 8a, the band where the coldest night of the year averaged 10 to 15°F (-12.2 to -9.4°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.