Frost Dates for 94028 — Portola Valley, California

Half of springs at Woodside Fire Stn 1, CA see their last 32°F night by February 25; only one in ten is past it by January 14, and one in ten still has one after April 11. Planting tender crops after March 13 leaves a 30% risk of a frost on them, after March 23 20%, and after April 11 10%. The 45 days between the even-odds date and the one-in-ten date is wider than at 93% 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 3 one year in ten, and holds off past December 19 one year in ten. A hard freeze of 28°F follows 17 days later, around December 12; in spring the one-in-ten date for 28°F is February 17, 53 days before the 32°F one. The freeze-free season lasts 274 days in a typical year, shorter than at 52% of the 219 California stations; it reaches 317 days one year in ten and falls short of 225 one year in ten. On average 26 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 44 days longer, to about April 10, and return around November 7. A 24°F night is unusual: 35% of winters had one.

August is the warmest month at Woodside Fire Stn 1, CA, averaging 89°F by day and 53°F at night; December is the coldest at 61°F and 37°F. From May to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 65% of years and March still brings one in 33% of years and April still brings one in 11% of years.

Warmth for growing adds up to 3,885 growing degree days a year (base 50°F), fewer than at 64% of the 283 California stations. 37% of them (1,441) have built up by the end of June, and August adds the most, 640.

The nearest other station, Palo Alto, CA, 6 miles northeast of Portola Valley and 355 feet lower, has a last frost 24 days earlier (February 1), a first frost 12 days later (December 7), a season 36 days longer.

Measurable snow is rare here: only 1 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Woodside Fire Stn 1, CA, 4.4 miles away, so there is no typical first-snow date to plan around.

ZIP 94028 is 4 miles from Woodside Fire Stn 1, CA, which stands at 380 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 94062 (Redwood City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 94028 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.