Eagle River climate

Eagle River Frost Dates and Growing Season

NOAA 1991-2020 normals for Copper Harbor, 31.6 km from Eagle River, elevation 626 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Copper Harbor. 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 10 and the first fall freeze around October 21, a growing season of about 161 days.

Median at 36°F
last May 27, first October 6
Median at 32°F
last May 10, first October 21
Median at 28°F
last April 27, first November 3

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 13Jun 7Jun 2May 31May 27May 24May 20May 15May 9
32°FJun 2May 26May 19May 14May 10May 7May 3Apr 30Apr 26
28°FMay 14May 6May 2Apr 30Apr 27Apr 24Apr 22Apr 19Apr 14
24°FApr 30Apr 25Apr 21Apr 19Apr 17Apr 14Apr 11Apr 8Apr 3
20°FApr 20Apr 16Apr 13Apr 9Apr 6Apr 4Apr 2Mar 31Mar 25
16°FApr 15Apr 9Apr 5Apr 3Apr 1Mar 30Mar 26Mar 21Mar 16

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 21Sep 27Oct 1Oct 3Oct 6Oct 9Oct 13Oct 16Oct 21
32°FOct 3Oct 9Oct 14Oct 18Oct 21Oct 24Oct 28Nov 1Nov 5
28°FOct 19Oct 26Oct 30Nov 1Nov 3Nov 5Nov 8Nov 12Nov 18
24°FNov 1Nov 4Nov 7Nov 10Nov 13Nov 15Nov 18Nov 22Nov 27
20°FNov 8Nov 12Nov 16Nov 19Nov 22Nov 25Nov 28Dec 1Dec 6
16°FNov 15Nov 20Nov 24Nov 28Dec 1Dec 2Dec 6Dec 11Dec 17

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°F155147141136131126120115108
32°F183176170165161155149142132
28°F207201195191187183179173164
24°F228222217213208204201196189
20°F247241236231227223219215208
16°F264256251246242238234229222

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
8,347
Cooling degree days, base 65°F
189
Growing degree days, base 40°F
3,273
Growing degree days, base 45°F
2,362
Growing degree days, base 50°F
1,586
Growing degree days, base 55°F
956
Growing degree days, base 60°F
486

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,37500
February1,25000
March1,14902
April81809
May493284
June23615239
July8574454
August6673473
September22424264
October573157
November88104
December1,20000

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 31.6 km from Eagle River. 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 USW00094899 (Copper Harbor). Public domain.