Frost Dates for 48189 — Whitmore Lake, Michigan

Half of springs at Whitmore Lake 1NW, MI see their last 32°F night by May 5; only one in ten is past it by April 22, and one in ten still has one after May 21. Planting tender crops after May 12 leaves a 30% risk of a frost on them, after May 16 20%, and after May 21 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 38% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 13 in half of years, as early as September 30 one year in ten, and holds off past October 26 one year in ten. A hard freeze of 28°F follows 13 days later, around October 26; in spring the one-in-ten date for 28°F is May 10, 11 days before the 32°F one. The freeze-free season lasts 160 days in a typical year, longer than at 51% of the 172 Michigan stations; it reaches 180 days one year in ten and falls short of 140 one year in ten. On average 152 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 12 days longer, to about May 17, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 28 and March 22.

July is the warmest month at Whitmore Lake 1NW, MI, averaging 82°F by day and 59°F at night; January is the coldest at 30°F and 15°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 66% of years.

Warmth for growing adds up to 2,470 growing degree days a year (base 50°F), more than at 50% of the 172 Michigan stations. 32% of them (786) have built up by the end of June, and July adds the most, 625.

The nearest other station, Ann Arbor U Of Mich, MI, 10 miles southeast of Whitmore Lake, has a last frost 2 days earlier (May 3), the same first-frost date.

The first measurable snow (0.1 inch or more) in Whitmore Lake usually arrives around November 10, and the last of the season around April 15. Those are the middle dates across the winters of 1991–2020 at Ann Arbor U Of Mich, MI, 10.5 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 20 days after the last snow.

ZIP 48189 is under a mile from Whitmore Lake 1NW, MI, which stands at 906 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 48178 (South Lyon). The 2023 USDA Plant Hardiness Zone Map lists ZIP 48189 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.