Frost Dates for 37148 — Portland, Tennessee

Half of springs at Portland Sewage Plt, TN see their last 32°F night by April 5; only one in ten is past it by March 21, and one in ten still has one after April 19. Planting tender crops after April 10 leaves a 30% risk of a frost on them, after April 13 20%, and after April 19 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 95% of the 144 Tennessee stations behind this site's ZIP pages.

In fall the first 32°F night comes by November 1 in half of years, as early as October 21 one year in ten, and holds off past November 14 one year in ten. A hard freeze of 28°F follows 10 days later, around November 11; in spring the one-in-ten date for 28°F is April 9, 10 days before the 32°F one. The freeze-free season lasts 210 days in a typical year, longer than at 69% of the 144 Tennessee stations; it reaches 231 days one year in ten and falls short of 192 one year in ten. On average 80 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 16, and return around October 23. Severe cold of 16°F or below comes in 99% of winters, usually between December 22 and February 16.

July is the warmest month at Portland Sewage Plt, TN, averaging 89°F by day and 69°F at night; January is the coldest at 45°F and 27°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 63% of years.

Warmth for growing adds up to 4,529 growing degree days a year (base 50°F), more than at 58% of the 144 Tennessee stations. 38% of them (1,719) have built up by the end of June, and July adds the most, 888. Precipitation totals 54.4 inches a year, most in May (5.8") and least in September (3.6"); May to September bring 42% of it.

The nearest other station, White House, TN, 11 miles southwest of Portland, has a last frost 2 days later (April 7), a first frost 2 days earlier (October 30), a season 4 days shorter.

The first measurable snow (0.1 inch or more) in Portland usually arrives around January 18, and the last of the season around February 7. Those are the middle dates across the winters of 1991–2020 at Portland Sewage Plt, TN, 1.1 miles away: half of years saw snow earlier, half later. Snow fell in 57% of those winters. The last 32°F night of spring typically comes 57 days after the last snow.

ZIP 37148 is 1 mile from Portland Sewage Plt, TN, which stands at 794 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 37148 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°C) over 1991–2020; a zone describes winter lows, not frost dates.