USDA Hardiness Zone 9a
Frost Dates for 85145 — Red Rock, Arizona
NOAA 1991–2020 normals from Picacho 8 SE, AZ (1,981 ft), 6 miles northwest.
Updated
In Red Rock, the last spring frost (32°F) is around February 6 in half of years and has passed by March 5 in nine years out of ten. The first fall frost comes around December 9, as early as November 22 one year in ten, leaving a typical freeze-free season of 308 days (NOAA, Picacho 8 SE, AZ).
- Last spring frost
- February 6
- First fall frost
- December 9
- Growing season
- 308 days
- Hardiness zone
- 9a
50% probability
50% probability
freeze-free, 50%
20 to 25°F (-6.7 to -3.9°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 20 observed
NOAA normal
Frost risk by date in Red Rock
Half of springs at Picacho 8 SE, AZ see their last 32°F night by February 6; only one in ten is past it by January 6, and one in ten still has one after March 5. Planting tender crops after February 18 leaves a 30% risk of a frost on them, after February 25 20%, and after March 5 10%. The 27 days between the even-odds date and the one-in-ten date is wider than at 71% of the 98 Arizona stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by December 9 in half of years, as early as November 22 one year in ten, and holds off past December 26 one year in ten. A hard freeze of 28°F follows 10 days later, around December 19; in spring the one-in-ten date for 28°F is February 13, 20 days before the 32°F one. The freeze-free season lasts 308 days in a typical year, longer than at 77% of the 98 Arizona stations; it reaches 340 days one year in ten and falls short of 276 one year in ten. On average 10 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 22 days longer, to about February 28, and return around November 29. A 24°F night is unusual: 36% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 2 | Feb 10 | Feb 18 | Feb 23 | Feb 28 | Mar 5 | Mar 10 | Mar 16 | Mar 26 |
| 32°F99% of yrs | Jan 6 | Jan 15 | Jan 24 | Feb 1 | Feb 6 | Feb 12 | Feb 18 | Feb 25 | Mar 5 |
| 28°F83% of yrs | Dec 17 | Dec 26 | Jan 1 | Jan 7 | Jan 14 | Jan 23 | Jan 29 | Feb 4 | Feb 13 |
| 24°F36% of yrs | too rare for a date | ||||||||
| 20°F7% of yrs | too rare for a date | ||||||||
| 16°F0% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 11 | Nov 17 | Nov 22 | Nov 26 | Nov 29 | Dec 2 | Dec 5 | Dec 9 | Dec 15 |
| 32°F99% of yrs | Nov 22 | Nov 27 | Dec 1 | Dec 5 | Dec 9 | Dec 12 | Dec 16 | Dec 20 | Dec 26 |
| 28°F83% of yrs | Dec 1 | Dec 7 | Dec 11 | Dec 15 | Dec 19 | Dec 25 | Dec 28 | Jan 5 | Jan 22 |
| 24°F36% of yrs | too rare for a date | ||||||||
| 20°F7% of yrs | too rare for a date | ||||||||
| 16°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Picacho 8 SE, 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 85145 →Compare Red Rock with another place →
Weather by month in Red Rock
July is the warmest month at Picacho 8 SE, AZ, averaging 104°F by day and 78°F at night; December is the coldest at 66°F and 40°F. A freezing night is all but certain in December (a 90% chance or more). From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 52% of years and March still brings one in 14% of years.
Warmth for growing adds up to 8,248 growing degree days a year (base 50°F), more than at 82% of the 102 Arizona stations. 41% of them (3,396) have built up by the end of June, and July adds the most, 1,279. Precipitation totals 10.1 inches a year, most in August (1.9") and least in May (0.2"); May to September bring 45% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 67 | 41 | 1.0 | 84% | 3 | 150 |
| Feb | 71 | 43 | 1.2 | 52% | 1 | 209 |
| Mar | 78 | 48 | 0.9 | 14% | <1 | 407 |
| Apr | 86 | 54 | 0.3 | 0% | 0 | 599 |
| May | 95 | 63 | 0.2 | 0% | 0 | 891 |
| Jun | 104 | 72 | 0.2 | 0% | 0 | 1141 |
| Jul | 104 | 78 | 1.3 | 0% | 0 | 1279 |
| Aug | 103 | 78 | 1.9 | 0% | 0 | 1243 |
| Sep | 99 | 72 | 0.9 | 0% | 0 | 1059 |
| Oct | 89 | 60 | 0.5 | 0% | 0 | 761 |
| Nov | 76 | 49 | 0.5 | 26% | 1 | 381 |
| Dec | 66 | 40 | 1.2 | 91% | 4 | 130 |
Monthly normals 1991–2020 at Picacho 8 SE, AZ (1,981 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, Arizona City, AZ, 22 miles northwest of Red Rock and 456 feet lower, has a last frost 22 days later (February 28), a first frost 18 days earlier (November 21), a season 42 days shorter.
When it snows in Red Rock, Arizona
Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Picacho 8 SE, AZ, 5.8 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 85145
| When | What to do |
|---|---|
| November 28 – December 12 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| December 12 – December 26 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 9 – January 23 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 6 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 16 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 25 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 9 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 85145 is 6 miles from Picacho 8 SE, AZ, which stands at 1,981 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 85145 in zone 9a, the band where the coldest night of the year averaged 20 to 25°F (-6.7 to -3.9°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.