Frost Dates for 63084 — Union, Missouri

Half of springs at Union, MO see their last 32°F night by April 11; only one in ten is past it by March 26, and one in ten still has one after April 28. Planting tender crops after April 17 leaves a 30% risk of a frost on them, after April 21 20%, and after April 28 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 23 in half of years, as early as October 9 one year in ten, and holds off past November 5 one year in ten. A hard freeze of 28°F follows 11 days later, around November 3; in spring the one-in-ten date for 28°F is April 15, 13 days before the 32°F one. The freeze-free season lasts 194 days in a typical year, shorter than at 50% of the 158 Missouri stations; it reaches 216 days one year in ten and falls short of 173 one year in ten. On average 101 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 11 days longer, to about April 22, and return around October 13. Severe cold of 16°F or below comes every winter, usually between December 7 and February 28.

July is the warmest month at Union, MO, averaging 91°F by day and 67°F at night; January is the coldest at 43°F and 23°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 79% of years.

Warmth for growing adds up to 4,333 growing degree days a year (base 50°F), more than at 84% of the 158 Missouri stations. 38% of them (1,634) have built up by the end of June, and July adds the most, 899. Precipitation totals 45.0 inches a year, most in April (5.0") and least in February (2.5"); May to September bring 47% of it.

The nearest other station, Washington, MO, 8 miles north of Union, has a last frost 3 days earlier (April 8), a first frost 2 days later (October 25), a season 5 days longer.

The first measurable snow (0.1 inch or more) in Union usually arrives around December 1, and the last of the season around March 14. Those are the middle dates across the winters of 1991–2020 at Union, MO, 0.7 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 28 days after the last snow.

ZIP 63084 is under a mile from Union, MO, which stands at 540 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 63084 in zone 6b, the band where the coldest night of the year averaged -5 to 0°F (-20.6 to -17.8°C) over 1991–2020; a zone describes winter lows, not frost dates.