Frost Dates for 49870 — Norway, Michigan

Half of springs at Iron Mountain-Kingsford Wwtp, MI see their last 32°F night by May 17; only one in ten is past it by May 2, and one in ten still has one after May 31. Planting tender crops after May 23 leaves a 30% risk of a frost on them, after May 26 20%, and after May 31 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 80% of the 172 Michigan stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 1 in half of years, as early as September 17 one year in ten, and holds off past October 13 one year in ten. A hard freeze of 28°F follows 10 days later, around October 11; in spring the one-in-ten date for 28°F is May 19, 12 days before the 32°F one. The freeze-free season lasts 135 days in a typical year, shorter than at 78% of the 172 Michigan stations; it reaches 153 days one year in ten and falls short of 118 one year in ten. On average 182 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 29, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 16 and April 5.

July is the warmest month at Iron Mountain-Kingsford Wwtp, MI, averaging 80°F by day and 57°F at night; January is the coldest at 24°F and 4°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month.

Warmth for growing adds up to 2,062 growing degree days a year (base 50°F), fewer than at 73% of the 172 Michigan stations. 31% of them (638) have built up by the end of June, and July adds the most, 574. Precipitation totals 31.7 inches a year, most in June (3.7") and least in February (1.2"); May to September bring 56% of it.

The nearest other station, Iron Mountain Ford Airport, MI, 10 miles west of Norway, has a last frost 8 days later (May 25), a first frost 7 days earlier (September 24), a season 14 days shorter.

The first measurable snow (0.1 inch or more) in Norway usually arrives around November 9, and the last of the season around April 15. Those are the middle dates across the winters of 1991–2020 at Iron Mountain-Kingsford Wwtp, MI, 8.5 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 32 days after the last snow.

ZIP 49870 is 9 miles from Iron Mountain-Kingsford Wwtp, MI, which stands at 1,071 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 49802 (Kingsford). The 2023 USDA Plant Hardiness Zone Map lists ZIP 49870 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.