Frost Dates for 65606 — Alton, Missouri

Half of springs at Alton, MO see their last 32°F night by April 17; only one in ten is past it by March 30, and one in ten still has one after May 1. Planting tender crops after April 23 leaves a 30% risk of a frost on them, after April 27 20%, and after May 1 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 80% of the 158 Missouri stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 21 in half of years, as early as October 7 one year in ten, and holds off past November 3 one year in ten. A hard freeze of 28°F follows 9 days later, around October 30; in spring the one-in-ten date for 28°F is April 22, 9 days before the 32°F one. The freeze-free season lasts 187 days in a typical year, shorter than at 73% of the 158 Missouri stations; it reaches 210 days one year in ten and falls short of 166 one year in ten. On average 110 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 27, and return around October 11. Severe cold of 16°F or below comes every winter, usually between December 3 and March 1.

July is the warmest month at Alton, MO, averaging 88°F by day and 66°F at night; January is the coldest at 44°F and 22°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 86% of years and May still brings one in 13% of years.

Warmth for growing adds up to 3,981 growing degree days a year (base 50°F), fewer than at 56% of the 158 Missouri stations. 37% of them (1,480) have built up by the end of June, and July adds the most, 840. Precipitation totals 47.4 inches a year, most in May (5.6") and least in January (3.0"); May to September bring 43% of it.

The nearest other station, Mammoth Spring, AR, 16 miles southwest of Alton and 311 feet lower, has a last frost 5 days earlier (April 12), a first frost 3 days later (October 24), a season 7 days longer.

The first measurable snow (0.1 inch or more) in Alton usually arrives around January 2, and the last of the season around February 9. Those are the middle dates across the winters of 1991–2020 at Alton, MO, 2.2 miles away: half of years saw snow earlier, half later. Snow fell in 79% of those winters. The last 32°F night of spring typically comes 67 days after the last snow.

ZIP 65606 is 2 miles from Alton, MO, which stands at 813 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 65606 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.