Mountain Iron climate

Mountain Iron Frost Dates and Growing Season

NOAA 1991-2020 normals for Eveleth Wwtp, 10.8 km from Mountain Iron, elevation 1445 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Eveleth Wwtp. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around May 12 and the first fall freeze around October 1, a growing season of about 141 days.

Median at 36°F
last May 24, first September 22
Median at 32°F
last May 12, first October 1
Median at 28°F
last May 3, first October 13

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FJun 6Jun 2May 30May 27May 24May 21May 19May 15May 10
32°FMay 28May 23May 19May 15May 12May 9May 7May 4Apr 30
28°FMay 16May 11May 8May 5May 3May 1Apr 29Apr 25Apr 20
24°FMay 7May 3Apr 30Apr 27Apr 24Apr 21Apr 17Apr 14Apr 9
20°FApr 28Apr 23Apr 20Apr 16Apr 13Apr 11Apr 8Apr 6Apr 2
16°FApr 20Apr 15Apr 11Apr 9Apr 6Apr 4Apr 2Mar 30Mar 23

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 9Sep 13Sep 16Sep 19Sep 22Sep 24Sep 27Sep 29Oct 3
32°FSep 18Sep 23Sep 26Sep 28Oct 1Oct 3Oct 6Oct 9Oct 14
28°FSep 29Oct 2Oct 6Oct 9Oct 13Oct 16Oct 19Oct 22Oct 27
24°FOct 9Oct 15Oct 19Oct 22Oct 26Oct 28Nov 1Nov 3Nov 8
20°FOct 21Oct 26Oct 30Nov 1Nov 3Nov 6Nov 9Nov 12Nov 17
16°FOct 30Nov 1Nov 5Nov 8Nov 10Nov 13Nov 15Nov 19Nov 25

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F138132127123120116113108102
32°F159153148144141138133128122
28°F181174170165161157153147142
24°F204197192187184180175171164
20°F221214209206203199194190183
16°F237229224220217213210205199

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
9,718
Cooling degree days, base 65°F
228
Growing degree days, base 40°F
3,362
Growing degree days, base 45°F
2,484
Growing degree days, base 50°F
1,723
Growing degree days, base 55°F
1,081
Growing degree days, base 60°F
573

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,78200
February1,48700
March1,24602
April801016
May4159143
June14041355
July5498508
August7766455
September29514207
October709035
November1,13401
December1,57800

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 10.8 km from Mountain Iron. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00212645 (Eveleth Wwtp). Public domain.