USDA Hardiness Zone 9a
Frost Dates for 94931 — Cotati, California
NOAA 1991–2020 normals from Petaluma Airport, CA (20 ft), 7 miles southeast.
Updated
In Cotati, the last spring frost (32°F) is around February 28 in half of years and has passed by April 6 in nine years out of ten. The first fall frost comes around November 25, as early as November 9 one year in ten, leaving a typical freeze-free season of 271 days (NOAA, Petaluma Airport, CA).
- Last spring frost
- February 28
- First fall frost
- November 25
- Growing season
- 271 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 18 observed
NOAA normal
Frost risk by date in Cotati
Half of springs at Petaluma Airport, CA see their last 32°F night by February 28; only one in ten is past it by January 24, and one in ten still has one after April 6. Planting tender crops after March 13 leaves a 30% risk of a frost on them, after March 26 20%, and after April 6 10%. The 37 days between the even-odds date and the one-in-ten date is wider than at 79% 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 November 25 in half of years, as early as November 9 one year in ten, and holds off past December 16 one year in ten. A hard freeze of 28°F follows 14 days later, around December 9; in spring the one-in-ten date for 28°F is February 24, 41 days before the 32°F one. The freeze-free season lasts 271 days in a typical year, shorter than at 55% of the 219 California stations; it reaches 313 days one year in ten and falls short of 230 one year in ten. On average 21 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 37 days longer, to about April 6, and return around November 10. A 24°F night is unusual: 41% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 7 | Mar 19 | Mar 28 | Apr 1 | Apr 6 | Apr 11 | Apr 15 | Apr 21 | Apr 27 |
| 32°F | Jan 24 | Feb 4 | Feb 14 | Feb 23 | Feb 28 | Mar 6 | Mar 13 | Mar 26 | Apr 6 |
| 28°F88% of yrs | Dec 17 | Dec 27 | Jan 3 | Jan 10 | Jan 17 | Jan 25 | Jan 31 | Feb 9 | Feb 24 |
| 24°F41% of yrs | too rare for a date | ||||||||
| 20°F6% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 27 | Nov 1 | Nov 3 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 22 | Nov 28 |
| 32°F | Nov 9 | Nov 14 | Nov 18 | Nov 22 | Nov 25 | Nov 29 | Dec 2 | Dec 7 | Dec 16 |
| 28°F88% of yrs | Nov 20 | Nov 28 | Dec 2 | Dec 5 | Dec 9 | Dec 14 | Dec 22 | Jan 1 | Jan 12 |
| 24°F41% of yrs | too rare for a date | ||||||||
| 20°F6% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Petaluma Airport, 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 94931 →Compare Cotati with another place →
Weather by month in Cotati
August is the warmest month at Petaluma Airport, CA, averaging 81°F by day and 53°F at night; December is the coldest at 58°F and 38°F. From May to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 67% of years and March still brings one in 40% of years and April still brings one in 15% of years.
Warmth for growing adds up to 3,210 growing degree days a year (base 50°F), fewer than at 79% of the 283 California stations. 35% of them (1,125) have built up by the end of June, and August adds the most, 527. Precipitation totals 25.6 inches a year, most in February (5.2") and least in July (0.0"); May to September bring 5% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 58 | 39 | 4.8 | 80% | 6 | 32 |
| Feb | 61 | 40 | 5.2 | 67% | 3 | 66 |
| Mar | 65 | 42 | 3.3 | 40% | 1 | 120 |
| Apr | 68 | 44 | 1.7 | 15% | 1 | 180 |
| May | 72 | 47 | 0.9 | 0% | 0 | 299 |
| Jun | 78 | 50 | 0.3 | 0% | 0 | 427 |
| Jul | 81 | 52 | 0.0 | 0% | 0 | 515 |
| Aug | 81 | 53 | 0.1 | 0% | 0 | 527 |
| Sep | 82 | 51 | 0.1 | 0% | 0 | 495 |
| Oct | 76 | 48 | 1.3 | 2% | 0 | 372 |
| Nov | 66 | 42 | 2.7 | 62% | 3 | 140 |
| Dec | 58 | 38 | 5.2 | 84% | 8 | 37 |
Monthly normals 1991–2020 at Petaluma Airport, CA (20 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, Santa Rosa, CA, 9 miles north of Cotati, has a last frost 3 days earlier (February 25), a first frost 6 days later (December 1), a season 8 days longer.
When it snows in Cotati, California
Measurable snow is rare here: only 0 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Petaluma Airport, CA, 7.4 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 94931
| When | What to do |
|---|---|
| December 20 – January 3 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| January 3 – January 17 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| January 31 – February 14 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| February 28 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by September 2 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by November 11 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 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 94931 is 7 miles from Petaluma Airport, CA, which stands at 20 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 94954 (Petaluma). The 2023 USDA Plant Hardiness Zone Map lists ZIP 94931 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.
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.