Ontonagon County climate

Ontonagon County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ontonagon 6 Se, 9.7 km from Ontonagon County, elevation 790 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ontonagon 6 Se. 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 27 and the first fall freeze around October 1, a growing season of about 127 days.

Median at 36°F
last June 8, first September 17
Median at 32°F
last May 27, first October 1
Median at 28°F
last May 10, first October 14

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°FJul 1Jun 22Jun 16Jun 12Jun 8Jun 5Jun 2May 30May 24
32°FJun 13Jun 6Jun 2May 30May 27May 23May 19May 15May 7
28°FMay 29May 22May 18May 13May 10May 5May 1Apr 29Apr 25
24°FMay 14May 8May 3Apr 30Apr 28Apr 25Apr 22Apr 17Apr 12
20°FApr 30Apr 26Apr 22Apr 19Apr 16Apr 13Apr 10Apr 6Apr 2
16°FApr 21Apr 16Apr 12Apr 10Apr 7Apr 4Apr 2Mar 30Mar 24

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°FAug 26Sep 2Sep 8Sep 13Sep 17Sep 20Sep 24Sep 29Oct 3
32°FSep 14Sep 21Sep 25Sep 29Oct 1Oct 4Oct 7Oct 10Oct 16
28°FSep 28Oct 3Oct 7Oct 10Oct 14Oct 17Oct 21Oct 27Nov 1
24°FOct 11Oct 18Oct 23Oct 27Oct 31Nov 2Nov 4Nov 7Nov 11
20°FOct 28Nov 1Nov 4Nov 6Nov 8Nov 11Nov 14Nov 17Nov 22
16°FNov 4Nov 8Nov 11Nov 14Nov 17Nov 20Nov 23Nov 27Dec 1

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°F1231141081049892877865
32°F151143137132127123116111102
28°F180172166161157152146139130
24°F205198192188184179174168159
20°F226219213209206202198193186
16°F241235231227223220215210204

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
8,229
Cooling degree days, base 65°F
354
Growing degree days, base 40°F
3,803
Growing degree days, base 45°F
2,850
Growing degree days, base 50°F
2,020
Growing degree days, base 55°F
1,316
Growing degree days, base 60°F
752

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,48900
February1,28100
March1,11517
April720134
May37419178
June13465386
July54123535
August64100501
September20841298
October562476
November93006
December1,29900

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 9.7 km from Ontonagon County. 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 USC00206220 (Ontonagon 6 Se). Public domain.