Frost Dates for 78221 — San Antonio, Texas

Half of springs at San Antonio Stinson Airport, TX see their last 32°F night by February 20; only one in ten is past it by January 20, and one in ten still has one after March 13. Planting tender crops after March 2 leaves a 30% risk of a frost on them, after March 7 20%, and after March 13 10%. The 21 days between the even-odds date and the one-in-ten date is wider than at 50% of the 339 Texas 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 3 in half of years, as early as November 12 one year in ten, and holds off past January 1 one year in ten. A hard freeze of 28°F follows 20 days later, around December 23; in spring the one-in-ten date for 28°F is March 5, 8 days before the 32°F one. The freeze-free season lasts 291 days in a typical year, longer than at 83% of the 339 Texas stations; it reaches 325 days one year in ten and falls short of 258 one year in ten. On average 14 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 13 days longer, to about March 5, and return around November 21. Nights of 24°F, cold enough to damage hardier plants, come in 50% of winters and 16°F in 1%.

August is the warmest month at San Antonio Stinson Airport, TX, averaging 98°F by day and 76°F at night; January is the coldest at 65°F and 42°F. From April to October the chance of a 32°F night stays under 10% each month. In spring, February still brings one in 64% of years and March still brings one in 35% of years.

Warmth for growing adds up to 7,858 growing degree days a year (base 50°F), more than at 87% of the 351 Texas stations. 43% of them (3,395) have built up by the end of June, and August adds the most, 1,133. Precipitation totals 29.8 inches a year, most in May (3.9") and least in February (1.6"); May to September bring 49% of it.

The nearest other station, San Antonio Kelly AFB, TX, 6 miles northwest of San Antonio, has a last frost 2 days later (February 22), a first frost 1 day earlier (December 2), a season 7 days shorter.

Measurable snow is rare here: only 4 of 19 winters from 1991 to 2020 recorded 0.1 inch or more at San Antonio Incarnate Word, TX, 10.1 miles away, so there is no typical first-snow date to plan around.

ZIP 78221 is 2 miles from San Antonio Stinson Airport, TX, which stands at 571 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 9 other ZIP codes share the station; its figures are presented in full for 78223 (San Antonio). The 2023 USDA Plant Hardiness Zone Map lists ZIP 78221 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.