Frost Dates for 86515 — Window Rock, Arizona

Half of springs at Window Rock Airport, AZ see their last 32°F night by May 29; only one in ten is past it by May 12, and one in ten still has one after June 10. Planting tender crops after June 2 leaves a 30% risk of a frost on them, after June 6 20%, and after June 10 10%. The 12 days between the even-odds date and the one-in-ten date is the narrowest of the 98 Arizona stations behind this site's ZIP pages.

In fall the first 32°F night comes by September 28 in half of years, as early as September 16 one year in ten, and holds off past October 8 one year in ten. A hard freeze of 28°F follows 6 days later, around October 4; in spring the one-in-ten date for 28°F is June 1, 9 days before the 32°F one. The freeze-free season lasts 121 days in a typical year, shorter than at 97% of the 98 Arizona stations; it reaches 140 days one year in ten and falls short of 104 one year in ten. On average 196 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 10 days longer, to about June 8, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 4 and April 1.

July is the warmest month at Window Rock Airport, AZ, averaging 88°F by day and 55°F at night; December is the coldest at 46°F and 14°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 38% of years.

Warmth for growing adds up to 2,321 growing degree days a year (base 50°F), fewer than at 94% of the 102 Arizona stations. 29% of them (682) have built up by the end of June, and July adds the most, 668. Precipitation totals 11.5 inches a year, most in August (1.9") and least in June (0.3"); May to September bring 51% of it.

The nearest other station, Gallup Municipal Airport, NM, 19 miles southeast of Window Rock and 268 feet lower, has a last frost 2 days later (May 31), the same first-frost date, a season 2 days shorter.

The first measurable snow (0.1 inch or more) in Window Rock usually arrives around November 28, and the last of the season around April 10. Those are the middle dates across the winters of 1991–2020 at Gallup Sand & Gravel, NM, 22.7 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 49 days after the last snow.

ZIP 86515 is 1 mile from Window Rock Airport, AZ, which stands at 6,739 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station; its figures are presented in full for 86504 (Fort Defiance). The 2023 USDA Plant Hardiness Zone Map lists ZIP 86515 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.