Frost Dates for 93405 — San Luis Obispo, California

In the 68% of winters that bring a 32°F night, half of springs at San Luis Obispo Poly, CA see their last 32°F night by January 16; only one in ten is past it by December 11, and one in ten still has one after February 26. Counting the winters with no freeze at all, the risk of a 32°F night after February 26 is under 7% and after January 16 34%. The 41 days between the even-odds date and the one-in-ten date is wider than at 89% 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 25 in half of years, as early as November 25 one year in ten, and holds off past February 12 one year in ten. A hard freeze of 28°F is less common: it came in 20% of winters. The freeze-free season lasts 349 days in a typical year, longer than at 93% of the 219 California stations; it reaches 365 days one year in ten and falls short of 304 one year in ten. On average 3 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 43 days longer, to about February 28, and return around December 1. A 24°F night is unusual: 4% of winters had one.

August is the warmest month at San Luis Obispo Poly, CA, averaging 80°F by day and 55°F at night; December is the coldest at 64°F and 44°F. From March to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 22% of years.

Warmth for growing adds up to 3,929 growing degree days a year (base 50°F), fewer than at 63% of the 283 California stations. 38% of them (1,507) have built up by the end of June, and August adds the most, 535. Precipitation totals 22.5 inches a year, most in January (5.1") and least in August (0.0"); May to September bring 4% of it.

The nearest other station, San Luis Obispo Airport, CA, 4 miles southeast of San Luis Obispo, has a last frost 15 days later (January 31), a first frost 14 days earlier (December 11), a season 30 days shorter.

Measurable snow is rare here: only 0 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at San Luis Obispo Poly, CA, 3 miles away, so there is no typical first-snow date to plan around.

ZIP 93405 is 3 miles from San Luis Obispo Poly, CA, which stands at 308 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 93405 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.