Frost Dates for 95945 — Grass Valley, California

Half of springs at Grass Valley #2, CA see their last 32°F night by April 10; only one in ten is past it by March 17, and one in ten still has one after April 30. Planting tender crops after April 18 leaves a 30% risk of a frost on them, after April 23 20%, and after April 30 10%. The 20 days between the even-odds date and the one-in-ten date is narrower than at 88% of the 220 California stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 13 in half of years, as early as October 26 one year in ten, and holds off past December 1 one year in ten. A hard freeze of 28°F follows 18 days later, around December 1; in spring the one-in-ten date for 28°F is April 8, 22 days before the 32°F one. The freeze-free season lasts 215 days in a typical year, shorter than at 76% of the 219 California stations; it reaches 244 days one year in ten and falls short of 188 one year in ten. On average 61 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 18 days longer, to about April 28, and return around October 31. Nights of 24°F, cold enough to damage hardier plants, come in 84% of winters and 16°F in 2%.

July is the warmest month at Grass Valley #2, CA, averaging 88°F by day and 58°F at night; December is the coldest at 53°F and 33°F. A freezing night is all but certain in every month from December to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 74% of years.

Warmth for growing adds up to 3,206 growing degree days a year (base 50°F), fewer than at 80% of the 283 California stations. 30% of them (959) have built up by the end of June, and July adds the most, 716. Precipitation totals 53.2 inches a year, most in December (10.5") and least in July (0.0"); May to September bring 7% of it.

The nearest other station, Nevada City, CA, 3 miles north of Grass Valley and 381 feet higher, has a last frost 4 days later (April 14), a first frost 7 days later (November 20), a season 3 days longer.

The first measurable snow (0.1 inch or more) in Grass Valley usually arrives around December 17, and the last of the season around March 23. Those are the middle dates across the winters of 1991–2020 at Nevada City, CA, 3.2 miles away: half of years saw snow earlier, half later. Snow fell in 97% of those winters. The last 32°F night of spring typically comes 18 days after the last snow.

ZIP 95945 is 3 miles from Grass Valley #2, CA, which stands at 2,400 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 95945 in zone 9a, the band where the coldest night of the year averaged 20 to 25°F (-6.7 to -3.9°C) over 1991–2020; a zone describes winter lows, not frost dates.