Frost Dates for 63303 — Saint Charles, Missouri

Half of springs at St Peters 2 SE, MO see their last 32°F night by April 9; only one in ten is past it by March 27, and one in ten still has one after April 25. Planting tender crops after April 17 leaves a 30% risk of a frost on them, after April 21 20%, and after April 25 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 35% of the 158 Missouri stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 26 in half of years, as early as October 14 one year in ten, and holds off past November 7 one year in ten. A hard freeze of 28°F follows 10 days later, around November 5; in spring the one-in-ten date for 28°F is April 14, 11 days before the 32°F one. The freeze-free season lasts 198 days in a typical year, longer than at 60% of the 158 Missouri stations; it reaches 219 days one year in ten and falls short of 178 one year in ten. On average 103 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 14 days longer, to about April 23, and return around October 17. Severe cold of 16°F or below comes every winter, usually between December 10 and March 1.

July is the warmest month at St Peters 2 SE, MO, averaging 88°F by day and 68°F at night; January is the coldest at 39°F and 21°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 78% of years.

Warmth for growing adds up to 4,056 growing degree days a year (base 50°F), more than at 52% of the 158 Missouri stations. 37% of them (1,483) have built up by the end of June, and July adds the most, 862. Precipitation totals 42.4 inches a year, most in May (4.8") and least in January (2.4"); May to September bring 48% of it.

The nearest other station, St Charles Elm Pt, MO, 4 miles north of Saint Charles, has a last frost 1 day earlier (April 8), a first frost 3 days later (October 29), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Saint Charles usually arrives around December 6, and the last of the season around March 6. Those are the middle dates across the winters of 1991–2020 at St Peters 2 SE, MO, 2.7 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 34 days after the last snow.

ZIP 63303 is 3 miles from St Peters 2 SE, MO, which stands at 575 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 63376 (Saint Peters). The 2023 USDA Plant Hardiness Zone Map lists ZIP 63303 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.