USDA Hardiness Zone 9b
Frost Dates for 95562 — Rio Dell, California
NOAA 1991–2020 normals from Scotia, CA (136 ft), 1 miles southeast.
Updated
A freeze (32°F) reaches Rio Dell in 84% of winters. When it does, the first fall frost comes around December 19 and the last spring frost around February 1; after March 8 the chance of another is under 8%.
- Last spring frost
- February 1
- First fall frost
- December 19
- Winters with a freeze
- 84%
- Hardiness zone
- 9b
50%, in freezing years
50%, in freezing years
32°F or below, 1991–2020
25 to 30°F (-3.9 to -1.1°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 10%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
2 of 20 observed
NOAA normal
Frost risk by date in Rio Dell
In the 84% of winters that bring a 32°F night, half of springs at Scotia, CA see their last 32°F night by February 1; only one in ten is past it by December 17, and one in ten still has one after March 8. Counting the winters with no freeze at all, the risk of a 32°F night after March 8 is under 8% and after February 1 42%. The 35 days between the even-odds date and the one-in-ten date is wider than at 71% 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 19 in half of years, as early as November 19 one year in ten, and holds off past February 10 one year in ten. A hard freeze of 28°F is less common: it came in 20% of winters. The freeze-free season lasts 328 days in a typical year, longer than at 79% of the 219 California stations; it reaches 365 days one year in ten and falls short of 284 one year in ten. On average 6 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 41 days longer, to about March 14, and return around November 23. A 24°F night is unusual: 0% of winters had one.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Feb 1 | Feb 22 | Feb 28 | Mar 8 | Mar 14 | Mar 22 | Mar 28 | Apr 1 | Apr 9 |
| 32°F84% of yrs | Dec 17 | Dec 31 | Jan 8 | Jan 21 | Feb 1 | Feb 12 | Feb 20 | Feb 28 | Mar 8 |
| 28°F20% of yrs | too rare for a date | ||||||||
| 24°F0% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Nov 1 | Nov 7 | Nov 13 | Nov 18 | Nov 23 | Nov 28 | Dec 3 | Dec 10 | Dec 23 |
| 32°F84% of yrs | Nov 19 | Nov 30 | Dec 5 | Dec 12 | Dec 19 | Dec 27 | Jan 3 | Jan 13 | Feb 10 |
| 28°F20% of yrs | too rare for a date | ||||||||
| 24°F0% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Scotia, 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 95562 →Compare Rio Dell with another place →
Weather by month in Rio Dell
August is the warmest month at Scotia, CA, averaging 72°F by day and 54°F at night; December is the coldest at 55°F and 42°F. From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 32% of years and March still brings one in 16% of years.
Warmth for growing adds up to 2,346 growing degree days a year (base 50°F), fewer than at 90% of the 283 California stations. 34% of them (800) have built up by the end of June, and August adds the most, 400. Precipitation totals 47.7 inches a year, most in December (9.7") and least in July (0.1"); May to September bring 7% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 57 | 43 | 8.6 | 43% | 2 | 55 |
| Feb | 58 | 43 | 7.8 | 32% | 1 | 61 |
| Mar | 59 | 44 | 6.9 | 16% | <1 | 84 |
| Apr | 62 | 45 | 3.9 | 0% | 0 | 118 |
| May | 64 | 49 | 1.9 | 0% | 0 | 203 |
| Jun | 67 | 51 | 0.6 | 0% | 0 | 279 |
| Jul | 70 | 54 | 0.1 | 0% | 0 | 364 |
| Aug | 72 | 54 | 0.1 | 0% | 0 | 400 |
| Sep | 73 | 52 | 0.5 | 0% | 0 | 366 |
| Oct | 69 | 48 | 2.4 | 0% | 0 | 264 |
| Nov | 61 | 45 | 5.2 | 17% | 1 | 112 |
| Dec | 55 | 42 | 9.7 | 46% | 2 | 40 |
Monthly normals 1991–2020 at Scotia, CA (136 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, Eureka WFO Woodley Island, CA, 22 miles north of Rio Dell, has a last frost 21 days later (February 22), a first frost 12 days earlier (December 7), a season 35 days shorter.
When it snows in Rio Dell, California
Measurable snow is rare here: only 2 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Scotia, CA, 1 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 95562 is 1 mile from Scotia, CA, which stands at 136 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 95540 (Fortuna). The 2023 USDA Plant Hardiness Zone Map lists ZIP 95562 in zone 9b, the band where the coldest night of the year averaged 25 to 30°F (-3.9 to -1.1°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.