USDA Hardiness Zone 4a
Frost Dates for 54847 — Iron River, Wisconsin
NOAA 1991–2020 normals from Brule Rs, WI (1,000 ft), 10 miles west.
Updated
In Iron River, the last spring frost (32°F) is around May 24 in half of years and has passed by June 6 in nine years out of ten. The first fall frost comes around September 26, as early as September 9 one year in ten, leaving a typical freeze-free season of 124 days (NOAA, Brule Rs, WI).
- Last spring frost
- May 24
- First fall frost
- September 26
- Growing season
- 124 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
- November 4
- Last snow
- April 12
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
23 of 23 observed
NOAA normal
Frost risk by date in Iron River
Half of springs at Brule Rs, WI see their last 32°F night by May 24; only one in ten is past it by May 8, and one in ten still has one after June 6. Planting tender crops after May 30 leaves a 30% risk of a frost on them, after June 2 20%, and after June 6 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 84% of the 182 Wisconsin stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 26 in half of years, as early as September 9 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 10 days later, around October 6; in spring the one-in-ten date for 28°F is May 27, 10 days before the 32°F one. The freeze-free season lasts 124 days in a typical year, shorter than at 96% of the 182 Wisconsin stations; it reaches 146 days one year in ten and falls short of 103 one year in ten. On average 190 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 June 5, and return around September 14. Severe cold of 16°F or below comes every winter, usually between November 11 and April 5.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 22 | May 27 | May 30 | Jun 2 | Jun 5 | Jun 7 | Jun 10 | Jun 14 | Jun 21 |
| 32°F | May 8 | May 14 | May 18 | May 21 | May 24 | May 27 | May 30 | Jun 2 | Jun 6 |
| 28°F | Apr 26 | Apr 30 | May 2 | May 6 | May 9 | May 13 | May 16 | May 20 | May 27 |
| 24°F | Apr 13 | Apr 18 | Apr 22 | Apr 25 | Apr 28 | Apr 30 | May 3 | May 7 | May 12 |
| 20°F | Apr 2 | Apr 6 | Apr 9 | Apr 13 | Apr 15 | Apr 18 | Apr 21 | Apr 24 | Apr 29 |
| 16°F | Mar 24 | Mar 29 | Apr 1 | Apr 3 | Apr 5 | Apr 8 | Apr 11 | Apr 16 | Apr 22 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 30 | Sep 3 | Sep 7 | Sep 11 | Sep 14 | Sep 17 | Sep 20 | Sep 24 | Sep 29 |
| 32°F | Sep 9 | Sep 15 | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 9 |
| 28°F | Sep 20 | Sep 26 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 13 | Oct 17 | Oct 24 |
| 24°F | Oct 3 | Oct 9 | Oct 13 | Oct 17 | Oct 21 | Oct 24 | Oct 27 | Nov 1 | Nov 4 |
| 20°F | Oct 18 | Oct 24 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 16 |
| 16°F | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 13 | Nov 16 | Nov 20 | Nov 24 |
Freeze probabilities 1991–2020 at Brule Rs, WI, 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 54847 →Compare Iron River with another place →
Weather by month in Iron River
July is the warmest month at Brule Rs, WI, averaging 78°F by day and 55°F at night; January is the coldest at 20°F and 2°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 25% of years.
Warmth for growing adds up to 1,755 growing degree days a year (base 50°F), fewer than at 96% of the 182 Wisconsin stations. 29% of them (516) have built up by the end of June, and July adds the most, 511.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 20 | 2 | 100% | 31 | 0 |
| Feb | 26 | 5 | 100% | 28 | 0 |
| Mar | 37 | 18 | 100% | 29 | 3 |
| Apr | 50 | 29 | 100% | 22 | 20 |
| May | 64 | 40 | 96% | 7 | 144 |
| Jun | 73 | 50 | 25% | 1 | 349 |
| Jul | 78 | 55 | 0% | 0 | 511 |
| Aug | 75 | 54 | 1% | 0 | 452 |
| Sep | 67 | 46 | 64% | 3 | 228 |
| Oct | 53 | 35 | 100% | 14 | 45 |
| Nov | 38 | 23 | 100% | 25 | 4 |
| Dec | 25 | 10 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Brule Rs, WI (1,000 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, Ashland 3S, WI, 22 miles east of Iron River and 174 feet lower, has a last frost 4 days earlier (May 20), a first frost 6 days later (October 2), a season 9 days longer.
When it snows in Iron River, Wisconsin
The first measurable snow (0.1 inch or more) in Iron River usually arrives around November 4, and the last of the season around April 12. Those are the middle dates across the winters of 1991–2020 at Brule Rs, WI, 10.1 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 42 days after the last snow.
Planting calendar for 54847
| When | What to do |
|---|---|
| March 15 – March 29 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 29 – April 12 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 26 – May 10 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 24 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 4 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 12 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 26 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 54847 is 10 miles from Brule Rs, WI, which stands at 1,000 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 54847 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.
Frost dates across Wisconsin →
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.