Frost Dates for 92404 — San Bernardino, California

Half of springs at Lake Arrowhead, CA see their last 32°F night by May 5; only one in ten is past it by April 9, and one in ten still has one after May 31. Planting tender crops after May 18 leaves a 30% risk of a frost on them, after May 25 20%, and after May 31 10%. The 26 days between the even-odds date and the one-in-ten date is narrower than at 67% 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 2 in half of years, as early as October 12 one year in ten, and holds off past November 15 one year in ten. A hard freeze of 28°F follows 14 days later, around November 16; in spring the one-in-ten date for 28°F is May 12, 19 days before the 32°F one. The freeze-free season lasts 176 days in a typical year, shorter than at 87% of the 219 California stations; it reaches 206 days one year in ten and falls short of 148 one year in ten. On average 105 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 22 days longer, to about May 27, and return around October 18. Nights of 24°F, cold enough to damage hardier plants, come in 100% of winters and 16°F in 54%.

August is the warmest month at Lake Arrowhead, CA, averaging 82°F by day and 57°F at night; December is the coldest at 43°F and 29°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 56% of years.

Warmth for growing adds up to 2,367 growing degree days a year (base 50°F), fewer than at 89% of the 283 California stations. 26% of them (627) have built up by the end of June, and August adds the most, 603. Precipitation totals 38.0 inches a year, most in February (9.9") and least in July (0.1"); May to September bring 5% of it.

The nearest other station, Redlands, CA, 9 miles southeast of San Bernardino and 3,795 feet lower, has a last frost 98 days earlier (January 27), a first frost 47 days later (December 19), a season 153 days longer.

Measurable snow is rare here: only 0 of 20 winters from 1991 to 2020 recorded 0.1 inch or more at Redlands, CA, 8.6 miles away, so there is no typical first-snow date to plan around.

ZIP 92404 is 8 miles from Lake Arrowhead, CA, which stands at 5,205 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station; its figures are presented in full for 92407 (San Bernardino). The 2023 USDA Plant Hardiness Zone Map lists ZIP 92404 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.