Frost Dates for 47371 — Portland, Indiana

Half of springs at Portland 1 SW, IN see their last 32°F night by April 28; only one in ten is past it by April 13, and one in ten still has one after May 14. Planting tender crops after May 4 leaves a 30% risk of a frost on them, after May 8 20%, and after May 14 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 15 in half of years, as early as October 1 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 13 days later, around October 28; in spring the one-in-ten date for 28°F is May 2, 12 days before the 32°F one. The freeze-free season lasts 171 days in a typical year, shorter than at 84% of the 125 Indiana stations; it reaches 192 days one year in ten and falls short of 150 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 9 days longer, to about May 7, and return around October 5. Severe cold of 16°F or below comes every winter, usually between December 1 and March 14.

July is the warmest month at Portland 1 SW, IN, averaging 84°F by day and 62°F at night; January is the coldest at 34°F and 17°F. A freezing night is all but certain in every month from October 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 41% of years.

Warmth for growing adds up to 3,064 growing degree days a year (base 50°F), fewer than at 78% of the 125 Indiana stations. 35% of them (1,075) have built up by the end of June, and July adds the most, 707. Precipitation totals 40.0 inches a year, most in June (4.6") and least in December (2.4"); May to September bring 49% of it.

The nearest other station, Farmland 5 NNW, IN, 15 miles southwest of Portland, has a last frost 3 days earlier (April 25), a first frost 1 day later (October 16), a season 2 days longer.

The first measurable snow (0.1 inch or more) in Portland usually arrives around December 7, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Portland 1 SW, IN, 1.2 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 50 days after the last snow.

ZIP 47371 is 1 mile from Portland 1 SW, IN, which stands at 910 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 47371 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.