Frost Dates for 63131 — Saint Louis, Missouri

Half of springs at St Charles 7 SSW, MO see their last 32°F night by April 4; only one in ten is past it by March 20, and one in ten still has one after April 21. Planting tender crops after April 10 leaves a 30% risk of a frost on them, after April 14 20%, and after April 21 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 66% of the 158 Missouri stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 29 in half of years, as early as October 15 one year in ten, and holds off past November 11 one year in ten. A hard freeze of 28°F follows 10 days later, around November 8; in spring the one-in-ten date for 28°F is April 8, 13 days before the 32°F one. The freeze-free season lasts 206 days in a typical year, longer than at 85% of the 158 Missouri stations; it reaches 228 days one year in ten and falls short of 186 one year in ten. On average 106 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 12 days longer, to about April 16, and return around October 19. Severe cold of 16°F or below comes every winter, usually between December 11 and February 26.

July is the warmest month at St Charles 7 SSW, MO, averaging 89°F by day and 69°F at night; January is the coldest at 40°F and 22°F. A freezing night is all but certain in every month from November 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 66% of years.

Warmth for growing adds up to 4,318 growing degree days a year (base 50°F), more than at 83% of the 158 Missouri stations. 37% of them (1,614) have built up by the end of June, and July adds the most, 899. Precipitation totals 42.4 inches a year, most in May (5.2") and least in February (2.2"); May to September bring 48% of it.

The nearest other station, St Louis Sci Ctr, MO, 9 miles east of Saint Louis, has a last frost 3 days earlier (April 1), a first frost 6 days later (November 4), a season 12 days longer.

The first measurable snow (0.1 inch or more) in Saint Louis usually arrives around December 14, and the last of the season around February 17. Those are the middle dates across the winters of 1991–2020 at St Charles 7 SSW, MO, 6.6 miles away: half of years saw snow earlier, half later. Snow fell in 88% of those winters. The last 32°F night of spring typically comes 46 days after the last snow.

ZIP 63131 is 7 miles from St Charles 7 SSW, MO, which stands at 450 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 7 other ZIP codes share the station; its figures are presented in full for 63021 (Ballwin). The 2023 USDA Plant Hardiness Zone Map lists ZIP 63131 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.