Frost Dates for 94515 — Calistoga, California

Half of springs at Calistoga, CA see their last 32°F night by March 2; only one in ten is past it by January 19, and one in ten still has one after April 18. Planting tender crops after March 25 leaves a 30% risk of a frost on them, after April 4 20%, and after April 18 10%. The 47 days between the even-odds date and the one-in-ten date is wider than at 96% 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 23 in half of years, as early as November 1 one year in ten, and holds off past December 20 one year in ten. A hard freeze of 28°F follows 13 days later, around December 6; in spring the one-in-ten date for 28°F is March 6, 43 days before the 32°F one. The freeze-free season lasts 263 days in a typical year, shorter than at 60% of the 219 California stations; it reaches 313 days one year in ten and falls short of 208 one year in ten. On average 36 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 42 days longer, to about April 13, and return around November 4. A 24°F night is unusual: 42% of winters had one.

July is the warmest month at Calistoga, CA, averaging 90°F by day and 55°F at night; December is the coldest at 58°F and 39°F. From May to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 60% of years and March still brings one in 37% of years and April still brings one in 19% of years.

Warmth for growing adds up to 3,994 growing degree days a year (base 50°F), fewer than at 59% of the 283 California stations. 37% of them (1,459) have built up by the end of June, and July adds the most, 685. Precipitation totals 38.6 inches a year, most in December (8.0") and least in July (0.0"); May to September bring 5% of it.

The nearest other station, Angwin Pacific Union College, CA, 9 miles east of Calistoga and 1,315 feet higher, has a last frost 36 days later (April 7), a first frost 12 days later (December 5), a season 18 days shorter.

Measurable snow is rare here: only 0 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Calistoga, CA, 0.5 miles away, so there is no typical first-snow date to plan around.

ZIP 94515 is under a mile from Calistoga, CA, which stands at 400 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 94515 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.