Frost Dates for 84631 — Fillmore, Utah

Half of springs at Fillmore, UT see their last 32°F night by May 4; only one in ten is past it by April 18, and one in ten still has one after May 26. Planting tender crops after May 12 leaves a 30% risk of a frost on them, after May 18 20%, and after May 26 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 80% 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 14 in half of years, as early as September 30 one year in ten, and holds off past October 28 one year in ten. A hard freeze of 28°F follows 11 days later, around October 25; in spring the one-in-ten date for 28°F is May 9, 17 days before the 32°F one. The freeze-free season lasts 160 days in a typical year, longer than at 56% of the 66 Utah stations; it reaches 182 days one year in ten and falls short of 133 one year in ten. On average 138 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 16 days longer, to about May 20, and return around October 2. Severe cold of 16°F or below comes every winter, usually between November 25 and February 21.

July is the warmest month at Fillmore, UT, averaging 88°F by day and 60°F at night; December is the coldest at 38°F and 21°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 60% of years.

Warmth for growing adds up to 3,004 growing degree days a year (base 50°F), more than at 56% of the 66 Utah stations. 31% of them (939) have built up by the end of June, and July adds the most, 756. Precipitation totals 15.2 inches a year, most in March (1.7") and least in June (0.7"); May to September bring 32% of it.

The nearest other station, Richfield Radio Ksvc, UT, 18 miles southeast of Fillmore and 158 feet higher, has a last frost 17 days later (May 21), a first frost 20 days earlier (September 24), a season 35 days shorter.

The first measurable snow (0.1 inch or more) in Fillmore usually arrives around October 29, and the last of the season around April 21. Those are the middle dates across the winters of 1991–2020 at Fillmore, UT, 0.7 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 13 days after the last snow.

ZIP 84631 is under a mile from Fillmore, UT, which stands at 5,127 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 84631 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.