Frost Dates for 62002 — Alton, Illinois

Half of springs at Alton - Melvin Price L&D, IL see their last 32°F night by April 4; only one in ten is past it by March 18, and one in ten still has one after April 19. Planting tender crops after April 9 leaves a 30% risk of a frost on them, after April 13 20%, and after April 19 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 5 in half of years, as early as October 25 one year in ten, and holds off past November 21 one year in ten. A hard freeze of 28°F follows 11 days later, around November 16; in spring the one-in-ten date for 28°F is April 9, 10 days before the 32°F one. The freeze-free season lasts 214 days in a typical year, longer than at 99% of the 158 Illinois stations; it reaches 237 days one year in ten and falls short of 194 one year in ten. On average 85 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 10 days longer, to about April 14, and return around October 27. Severe cold of 16°F or below comes every winter, usually between December 15 and February 27.

July is the warmest month at Alton - Melvin Price L&D, IL, averaging 87°F by day and 69°F at night; January is the coldest at 39°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 62% of years.

Warmth for growing adds up to 4,168 growing degree days a year (base 50°F), more than at 91% of the 158 Illinois stations. 36% of them (1,518) have built up by the end of June, and July adds the most, 877. Precipitation totals 41.9 inches a year, most in May (5.5") and least in January (2.5"); May to September bring 47% of it.

The nearest other station, St Louis Lambert International Airport, MO, 16 miles southwest of Alton, has a last frost 2 days earlier (April 2), a first frost 1 day earlier (November 4), a season 1 day longer.

The first measurable snow (0.1 inch or more) in Alton usually arrives around December 15, and the last of the season around March 3. Those are the middle dates across the winters of 1991–2020 at Edwardsville 2 W, IL, 10.7 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 32 days after the last snow.

ZIP 62002 is 3 miles from Alton - Melvin Price L&D, IL, which stands at 405 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 13 other ZIP codes share the station; its figures are presented in full for 62040 (Granite City). The 2023 USDA Plant Hardiness Zone Map lists ZIP 62002 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.