USDA Hardiness Zone 9b
Frost Dates for 94552 — Castro Valley, California
NOAA 1991–2020 normals from Hayward Air Terminal, CA (43 ft), 6 miles southwest.
Updated
Frost is not a yearly event in Castro Valley: a night at or below 32°F came in 45% of the winters of 1991–2020 at Hayward Air Terminal, CA, and a 36°F night, cold enough for frost on exposed leaves, in 93%. There is no reliable "last frost date" here; most years have none.
- Winters with a freeze
- 45%
- Winters with 36°F
- 93%
- Coldest month low
- 43°F
- Hardiness zone
- 9b
32°F or below, 1991–2020
frost possible on leaves
average, December
25 to 30°F (-3.9 to -1.1°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 19 observed
NOAA normal
Frost risk by date in Castro Valley
At Hayward Air Terminal, CA, 6 miles southwest of Castro Valley, 45% of the winters of 1991–2020 had at least one night at or below 32°F, 5% reached 28°F. Nights of 36°F, enough for frost on exposed leaves, are more common (93% of winters) and, when they come, fall between about December 12 and January 29. December is the month most likely to bring one: a 29% chance in a given year. 62 of the 283 other California stations behind this site's ZIP pages freeze in fewer than half of winters too.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F93% of yrs | Dec 30 | Jan 7 | Jan 14 | Jan 22 | Jan 29 | Feb 3 | Feb 11 | Feb 21 | Feb 28 |
| 32°F45% of yrs | too rare for a date | ||||||||
| 28°F5% of yrs | too rare for a date | ||||||||
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F93% of yrs | Nov 24 | Dec 1 | Dec 4 | Dec 8 | Dec 12 | Dec 16 | Dec 22 | Dec 31 | Jan 11 |
| 32°F45% of yrs | too rare for a date | ||||||||
| 28°F5% of yrs | too rare for a date | ||||||||
Freeze probabilities 1991–2020 at Hayward Air Terminal, 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 94552 →Compare Castro Valley with another place →
Weather by month in Castro Valley
August is the warmest month at Hayward Air Terminal, CA, averaging 76°F by day and 58°F at night; December is the coldest at 59°F and 43°F. From February to November the chance of a 32°F night stays under 10% each month.
Warmth for growing adds up to 3,627 growing degree days a year (base 50°F), fewer than at 69% of the 283 California stations. 38% of them (1,392) have built up by the end of June, and August adds the most, 536. Precipitation totals 16.1 inches a year, most in December (3.2") and least in July (0.0"); May to September bring 6% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 59 | 43 | 2.9 | 24% | 1 | 73 |
| Feb | 62 | 45 | 3.1 | 2% | 0 | 113 |
| Mar | 64 | 47 | 2.4 | 0% | 0 | 188 |
| Apr | 67 | 50 | 1.2 | 0% | 0 | 245 |
| May | 69 | 52 | 0.6 | 0% | 0 | 336 |
| Jun | 74 | 55 | 0.2 | 0% | 0 | 437 |
| Jul | 75 | 57 | 0.0 | 0% | 0 | 498 |
| Aug | 76 | 58 | 0.1 | 0% | 0 | 536 |
| Sep | 77 | 58 | 0.1 | 0% | 0 | 519 |
| Oct | 74 | 54 | 0.8 | 0% | 0 | 419 |
| Nov | 65 | 47 | 1.5 | 0% | 0 | 191 |
| Dec | 59 | 43 | 3.2 | 29% | 1 | 74 |
Monthly normals 1991–2020 at Hayward Air Terminal, CA (43 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, Fremont, CA, 11 miles south of Castro Valley, has a 32°F night in 65% of winters against 45% here, and the same coolest-month low, 43°F.
When it snows in Castro Valley, California
Measurable snow is rare here: only 0 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at Upper San Leandro Filters, CA, 9.3 miles away, so there is no typical first-snow date to plan around.
Where these figures come from
ZIP 94552 is 6 miles from Hayward Air Terminal, CA, which stands at 43 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 8 other ZIP codes share the station; its figures are presented in full for 94544 (Hayward). The 2023 USDA Plant Hardiness Zone Map lists ZIP 94552 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.