Frost Dates for 94089 — Sunnyvale, California

In the 70% of winters that bring a 32°F night, half of springs at Moffett Federal Airfield, CA see their last 32°F night by January 6; only one in ten is past it by December 16, and one in ten still has one after February 4. Counting the winters with no freeze at all, the risk of a 32°F night after February 4 is under 7% and after January 6 35%. The 29 days between the even-odds date and the one-in-ten date is narrower than at 52% 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 23 in half of years, as early as December 3 one year in ten, and holds off past January 16 one year in ten. A hard freeze of 28°F is less common: it came in 14% of winters. The freeze-free season lasts 353 days in a typical year, longer than at 95% of the 219 California stations; it reaches 365 days one year in ten and falls short of 323 one year in ten. On average 2 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 31 days longer, to about February 6, and return around December 6. No night reached 24°F in 1991–2020.

August is the warmest month at Moffett Federal Airfield, CA, averaging 77°F by day and 59°F at night; December is the coldest at 59°F and 42°F. From February to November the chance of a 32°F night stays under 10% each month.

Warmth for growing adds up to 3,761 growing degree days a year (base 50°F), fewer than at 67% of the 283 California stations. 39% of them (1,463) have built up by the end of June, and August adds the most, 557. Precipitation totals 13.5 inches a year, most in February (2.9") and least in July (0.0"); May to September bring 4% of it.

The nearest other station, San Jose, CA, 6 miles southeast of Sunnyvale, has a last frost 6 days later (January 12), a first frost 1 day earlier (December 22), a season 6 days shorter.

Measurable snow is rare here: only 0 of 17 winters from 1991 to 2020 recorded 0.1 inch or more at San Jose, CA, 7 miles away, so there is no typical first-snow date to plan around.

ZIP 94089 is 2 miles from Moffett Federal Airfield, CA, which stands at 39 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 9 other ZIP codes share the station; its figures are presented in full for 95014 (Cupertino). The 2023 USDA Plant Hardiness Zone Map lists ZIP 94089 in zone 10a, the band where the coldest night of the year averaged 30 to 35°F (-1.1 to 1.7°C) over 1991–2020; a zone describes winter lows, not frost dates.