USDA Hardiness Zone 8a
Frost Dates for 92391 — Twin Peaks, California
NOAA 1991–2020 normals from Mitchell Caverns, CA (4,350 ft), 25 miles east.
Updated
In Twin Peaks, the last spring frost (32°F) is around March 6 in half of years and has passed by April 9 in nine years out of ten. The first fall frost comes around December 8, as early as November 12 one year in ten, leaving a typical freeze-free season of 272 days (NOAA, Mitchell Caverns, CA).
- Last spring frost
- March 6
- First fall frost
- December 8
- Growing season
- 272 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
- 0%
- Snow per year
- 0"
median, 1991–2020
median, 1991–2020
0 of 17 observed
NOAA normal
Frost risk by date in Twin Peaks
Half of springs at Mitchell Caverns, CA see their last 32°F night by March 6; only one in ten is past it by January 17, and one in ten still has one after April 9. Planting tender crops after March 21 leaves a 30% risk of a frost on them, after March 30 20%, and after April 9 10%. The 34 days between the even-odds date and the one-in-ten date is wider than at 65% of the 220 California 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 8 in half of years, as early as November 12 one year in ten, and holds off past January 5 one year in ten. A hard freeze of 28°F follows 17 days later, around December 25; in spring the one-in-ten date for 28°F is March 20, 20 days before the 32°F one. The freeze-free season lasts 272 days in a typical year, shorter than at 54% of the 219 California stations; it reaches 326 days one year in ten and falls short of 226 one year in ten. On average 22 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 26 days longer, to about April 1, and return around November 24. A 24°F night is unusual: 33% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 27 | Mar 10 | Mar 19 | Mar 27 | Apr 1 | Apr 7 | Apr 14 | Apr 23 | May 2 |
| 32°F99% of yrs | Jan 17 | Feb 6 | Feb 19 | Feb 28 | Mar 6 | Mar 12 | Mar 21 | Mar 30 | Apr 9 |
| 28°F80% of yrs | Dec 21 | Jan 1 | Jan 10 | Jan 22 | Feb 1 | Feb 14 | Feb 26 | Mar 6 | Mar 20 |
| 24°F33% of yrs | too rare for a date | ||||||||
| 20°F6% 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 | Oct 30 | Nov 8 | Nov 14 | Nov 20 | Nov 24 | Nov 28 | Dec 3 | Dec 7 | Dec 14 |
| 32°F99% of yrs | Nov 12 | Nov 22 | Nov 28 | Dec 3 | Dec 8 | Dec 12 | Dec 17 | Dec 24 | Jan 5 |
| 28°F80% of yrs | Nov 25 | Dec 3 | Dec 9 | Dec 16 | Dec 25 | Dec 31 | Jan 9 | Jan 25 | Feb 13 |
| 24°F33% of yrs | too rare for a date | ||||||||
| 20°F6% of yrs | too rare for a date | ||||||||
| 16°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Mitchell Caverns, CA, 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 92391 →Compare Twin Peaks with another place →
Weather by month in Twin Peaks
July is the warmest month at Mitchell Caverns, CA, averaging 92°F by day and 73°F at night; December is the coldest at 53°F and 40°F. From May to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 62% of years and March still brings one in 49% of years and April still brings one in 17% of years.
Warmth for growing adds up to 5,424 growing degree days a year (base 50°F), more than at 77% of the 283 California stations. 36% of them (1,941) have built up by the end of June, and July adds the most, 1,012. Precipitation totals 10.7 inches a year, most in February (1.8") and least in June (0.1"); May to September bring 25% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 54 | 40 | 1.3 | 80% | 5 | 48 |
| Feb | 55 | 41 | 1.8 | 62% | 4 | 62 |
| Mar | 62 | 45 | 1.6 | 49% | 2 | 162 |
| Apr | 68 | 50 | 0.6 | 17% | 1 | 281 |
| May | 77 | 58 | 0.2 | 1% | <1 | 549 |
| Jun | 87 | 69 | 0.1 | 0% | 0 | 838 |
| Jul | 92 | 73 | 1.1 | 0% | 0 | 1012 |
| Aug | 91 | 72 | 0.6 | 0% | 0 | 980 |
| Sep | 85 | 68 | 0.7 | 0% | 0 | 792 |
| Oct | 74 | 57 | 0.6 | 3% | <1 | 474 |
| Nov | 62 | 47 | 0.5 | 33% | 2 | 182 |
| Dec | 53 | 40 | 1.6 | 81% | 6 | 43 |
Monthly normals 1991–2020 at Mitchell Caverns, CA (4,350 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
When it snows in Twin Peaks, California
Measurable snow is rare here: only 0 of 17 winters from 1991 to 2020 recorded 0.1 inch or more at Baker, CA, 30.6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 92391
| When | What to do |
|---|---|
| December 26 – January 9 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| January 9 – January 23 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| February 6 – February 20 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| March 6 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 15 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 24 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| December 8 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 92391 is 25 miles from Mitchell Caverns, CA, which stands at 4,350 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 91708 (Chino). The 2023 USDA Plant Hardiness Zone Map lists ZIP 92391 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.
Frost dates across California →
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.