Frost Dates for 84121 — Salt Lake City, Utah

Half of springs at Cottonwood Weir, UT see their last 32°F night by April 29; only one in ten is past it by April 10, and one in ten still has one after May 30. Planting tender crops after May 8 leaves a 30% risk of a frost on them, after May 15 20%, and after May 30 10%. The 31 days between the even-odds date and the one-in-ten date is the widest of the 66 Utah stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by October 22 in half of years, as early as October 6 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 1; in spring the one-in-ten date for 28°F is May 13, 17 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, longer than at 67% of the 66 Utah stations; it reaches 200 days one year in ten and falls short of 143 one year in ten. On average 112 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 14 days longer, to about May 13, and return around October 11. Severe cold of 16°F or below comes every winter, usually between December 2 and February 13.

July is the warmest month at Cottonwood Weir, UT, averaging 91°F by day and 68°F at night; January is the coldest at 38°F and 23°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 41% of years.

Warmth for growing adds up to 3,539 growing degree days a year (base 50°F), more than at 83% of the 66 Utah stations. 30% of them (1,051) have built up by the end of June, and July adds the most, 902. Precipitation totals 24.4 inches a year, most in April (3.3") and least in July (0.6"); May to September bring 30% of it.

The nearest other station, Salt Lake City E Bench, UT, 8 miles north of Salt Lake City, has a last frost 4 days earlier (April 25), a first frost 4 days earlier (October 18), a season 1 day longer.

The first measurable snow (0.1 inch or more) in Salt Lake City usually arrives around November 19, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at Cottonwood Weir, UT, 1.8 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 21 days after the last snow.

ZIP 84121 is 2 miles from Cottonwood Weir, UT, which stands at 4,986 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 8 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 84121 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.