Frost Dates for 46504 — Bourbon, Indiana

Half of springs at Plymouth, IN see their last 32°F night by April 25; only one in ten is past it by April 12, and one in ten still has one after May 13. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 6 20%, and after May 13 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 84% of the 125 Indiana 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 5 one year in ten, and holds off past November 3 one year in ten. A hard freeze of 28°F follows 11 days later, around November 1; in spring the one-in-ten date for 28°F is April 30, 13 days before the 32°F one. The freeze-free season lasts 178 days in a typical year, shorter than at 62% of the 125 Indiana stations; it reaches 197 days one year in ten and falls short of 156 one year in ten. On average 132 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 May 6, and return around October 9. Severe cold of 16°F or below comes every winter, usually between December 3 and March 13.

July is the warmest month at Plymouth, IN, averaging 84°F by day and 63°F at night; January is the coldest at 31°F and 17°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 33% of years.

Warmth for growing adds up to 3,099 growing degree days a year (base 50°F), fewer than at 73% of the 125 Indiana stations. 35% of them (1,072) have built up by the end of June, and July adds the most, 721. Precipitation totals 40.2 inches a year, most in July (4.4") and least in February (2.3"); May to September bring 50% of it.

The nearest other station, Warsaw, IN, 13 miles east of Bourbon, has a last frost 3 days later (April 28), a first frost 3 days earlier (October 18), a season 8 days shorter.

The first measurable snow (0.1 inch or more) in Bourbon usually arrives around November 23, and the last of the season around April 4. Those are the middle dates across the winters of 1991–2020 at Plymouth, IN, 11.9 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 21 days after the last snow.

ZIP 46504 is 12 miles from Plymouth, IN, which stands at 815 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 46563 (Plymouth). The 2023 USDA Plant Hardiness Zone Map lists ZIP 46504 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°C) over 1991–2020; a zone describes winter lows, not frost dates.