Frost Dates for 46220 — Indianapolis, Indiana

Half of springs at Castleton 2 S, IN see their last 32°F night by April 18; only one in ten is past it by April 3, and one in ten still has one after May 6. Planting tender crops after April 25 leaves a 30% risk of a frost on them, after May 1 20%, and after May 6 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 26 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 10 days later, around November 5; in spring the one-in-ten date for 28°F is April 24, 12 days before the 32°F one. The freeze-free season lasts 190 days in a typical year, longer than at 70% of the 125 Indiana stations; it reaches 211 days one year in ten and falls short of 166 one year in ten. On average 113 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 12 days longer, to about April 30, and return around October 16. Severe cold of 16°F or below comes every winter, usually between December 6 and March 4.

July is the warmest month at Castleton 2 S, IN, averaging 85°F by day and 65°F at night; January is the coldest at 36°F and 20°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 20% of years.

Warmth for growing adds up to 3,518 growing degree days a year (base 50°F), more than at 62% of the 125 Indiana stations. 37% of them (1,300) have built up by the end of June, and July adds the most, 773. Precipitation totals 47.3 inches a year, most in June (5.6") and least in February (2.7"); May to September bring 48% of it.

The nearest other station, Carmel 3 E, IN, 7 miles northeast of Indianapolis, has a last frost 3 days later (April 21), a first frost 5 days earlier (October 21), a season 7 days shorter.

The first measurable snow (0.1 inch or more) in Indianapolis usually arrives around November 28, and the last of the season around March 18. Those are the middle dates across the winters of 1991–2020 at Castleton 2 S, IN, 3.9 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 31 days after the last snow.

ZIP 46220 is 4 miles from Castleton 2 S, IN, which stands at 824 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 12 other ZIP codes share the station; its figures are presented in full for 46226 (Indianapolis). The 2023 USDA Plant Hardiness Zone Map lists ZIP 46220 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.