USDA Hardiness Zone 4a
Frost Dates for 49935 — Iron River, Michigan
NOAA 1991–2020 normals from Stambaugh 2SSE, MI (1,450 ft), 5 miles southeast.
Updated
In Iron River, the last spring frost (32°F) is around June 4 in half of years and has passed by June 26 in nine years out of ten. The first fall frost comes around September 10, as early as August 21 one year in ten, leaving a typical freeze-free season of 95 days (NOAA, Stambaugh 2SSE, MI).
- Last spring frost
- June 4
- First fall frost
- September 10
- Growing season
- 95 days
- Hardiness zone
- 4a
50% probability
50% probability
freeze-free, 50%
-30 to -25°F (-34.4 to -31.7°C) coldest night
- First snow
- October 28
- Last snow
- April 18
- Winters with snow
- 100%
- Snow per year
- 67.4"
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Iron River
Half of springs at Stambaugh 2SSE, MI see their last 32°F night by June 4; only one in ten is past it by May 22, and one in ten still has one after June 26. Planting tender crops after June 12 leaves a 30% risk of a frost on them, after June 18 20%, and after June 26 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 98% of the 172 Michigan 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 September 10 in half of years, as early as August 21 one year in ten, and holds off past September 25 one year in ten. A hard freeze of 28°F follows 14 days later, around September 24; in spring the one-in-ten date for 28°F is June 6, 20 days before the 32°F one. The freeze-free season lasts 95 days in a typical year, shorter than at 99% of the 172 Michigan stations; it reaches 118 days one year in ten and falls short of 66 one year in ten. On average 211 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between November 1 and April 18.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 22 | May 26 | May 30 | Jun 1 | Jun 4 | Jun 8 | Jun 12 | Jun 18 | Jun 26 |
| 28°F | May 7 | May 12 | May 16 | May 20 | May 23 | May 26 | May 29 | Jun 1 | Jun 6 |
| 24°F | Apr 26 | Apr 30 | May 3 | May 7 | May 10 | May 13 | May 17 | May 21 | May 26 |
| 20°F | Apr 14 | Apr 19 | Apr 22 | Apr 25 | Apr 28 | Apr 30 | May 3 | May 8 | May 14 |
| 16°F | Apr 5 | Apr 9 | Apr 12 | Apr 16 | Apr 18 | Apr 21 | Apr 23 | Apr 27 | Apr 30 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 21 | Aug 29 | Sep 3 | Sep 6 | Sep 10 | Sep 13 | Sep 17 | Sep 20 | Sep 25 |
| 28°F | Sep 7 | Sep 13 | Sep 18 | Sep 21 | Sep 24 | Sep 28 | Oct 1 | Oct 3 | Oct 8 |
| 24°F | Sep 20 | Sep 26 | Sep 30 | Oct 2 | Oct 5 | Oct 9 | Oct 11 | Oct 16 | Oct 21 |
| 20°F | Oct 2 | Oct 7 | Oct 11 | Oct 15 | Oct 19 | Oct 22 | Oct 26 | Oct 30 | Nov 2 |
| 16°F | Oct 16 | Oct 23 | Oct 27 | Oct 31 | Nov 1 | Nov 4 | Nov 8 | Nov 12 | Nov 16 |
Freeze probabilities 1991–2020 at Stambaugh 2SSE, MI, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 49935 →Compare Iron River with another place →
Weather by month in Iron River
July is the warmest month at Stambaugh 2SSE, MI, averaging 77°F by day and 50°F at night; January is the coldest at 21°F and 0°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). July is the only month with under a 10% chance of a 32°F night. In spring, June still brings one in 59% of years.
Warmth for growing adds up to 1,442 growing degree days a year (base 50°F), fewer than at 99% of the 172 Michigan stations. 31% of them (454) have built up by the end of June, and July adds the most, 426. Precipitation totals 30.8 inches a year, most in July (4.2") and least in February (1.0"); May to September bring 58% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 21 | 0 | 1.1 | 100% | 31 | 0 |
| Feb | 26 | 0 | 1.0 | 100% | 28 | 0 |
| Mar | 37 | 9 | 1.5 | 100% | 30 | 2 |
| Apr | 50 | 24 | 2.6 | 100% | 26 | 13 |
| May | 64 | 37 | 3.2 | 100% | 11 | 127 |
| Jun | 73 | 47 | 4.0 | 59% | 2 | 312 |
| Jul | 77 | 50 | 4.2 | 7% | <1 | 426 |
| Aug | 75 | 48 | 3.1 | 23% | <1 | 357 |
| Sep | 67 | 41 | 3.5 | 94% | 6 | 174 |
| Oct | 53 | 31 | 3.3 | 100% | 20 | 30 |
| Nov | 38 | 21 | 1.8 | 100% | 27 | 2 |
| Dec | 26 | 9 | 1.5 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Stambaugh 2SSE, MI (1,450 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Amasa 1W, MI, 15 miles northeast of Iron River, has a last frost 2 days later (June 6), a first frost 1 day earlier (September 9), a season 1 day shorter.
When it snows in Iron River, Michigan
The first measurable snow (0.1 inch or more) in Iron River usually arrives around October 28, and the last of the season around April 18. Those are the middle dates across the winters of 1991–2020 at Stambaugh 2SSE, MI, 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 47 days after the last snow.
Planting calendar for 49935
| When | What to do |
|---|---|
| March 26 – April 9 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 9 – April 23 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 7 – May 21 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| June 4 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 18 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 27 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 10 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 49935 is 5 miles from Stambaugh 2SSE, MI, which stands at 1,450 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 49935 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.