Frost Dates for 47631 — New Harmony, Indiana

Half of springs at Grayville, IL see their last 32°F night by April 7; only one in ten is past it by March 24, and one in ten still has one after April 23. Planting tender crops after April 14 leaves a 30% risk of a frost on them, after April 18 20%, and after April 23 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 35% of the 125 Indiana stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 25 in half of years, as early as October 12 one year in ten, and holds off past November 7 one year in ten. A hard freeze of 28°F follows 11 days later, around November 5; in spring the one-in-ten date for 28°F is April 12, 11 days before the 32°F one. The freeze-free season lasts 201 days in a typical year, longer than at 86% of the 125 Indiana stations; it reaches 221 days one year in ten and falls short of 179 one year in ten. On average 97 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 13 days longer, to about April 20, and return around October 17. Severe cold of 16°F or below comes every winter, usually between December 10 and February 25.

July is the warmest month at Grayville, IL, averaging 89°F by day and 68°F at night; January is the coldest at 41°F and 24°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 72% of years.

Warmth for growing adds up to 4,206 growing degree days a year (base 50°F), more than at 92% of the 125 Indiana stations. 38% of them (1,594) have built up by the end of June, and July adds the most, 871. Precipitation totals 50.1 inches a year, most in May (5.8") and least in January (3.2"); May to September bring 46% of it.

The nearest other station, Mt Vernon, IN, 13 miles south of New Harmony, has the same 50% last-frost date, a first frost 3 days later (October 28), a season 1 day longer.

The first measurable snow (0.1 inch or more) in New Harmony usually arrives around December 19, and the last of the season around February 23. Those are the middle dates across the winters of 1991–2020 at Poseyville, IN, 8 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 43 days after the last snow.

ZIP 47631 is 12 miles from Grayville, IL, which stands at 435 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 47633 (Poseyville). The 2023 USDA Plant Hardiness Zone Map lists ZIP 47631 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.