Alpena County climate

Alpena County Frost Dates and Growing Season

NOAA 1991-2020 normals for Alpena Wwtp, 2.5 km from Alpena County, elevation 590 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Alpena 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 5 and the first fall freeze around October 17, a growing season of about 163 days.

Median at 36°F
last May 17, first October 4
Median at 32°F
last May 5, first October 17
Median at 28°F
last April 23, first October 31

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°FMay 30May 25May 22May 20May 17May 14May 10May 6May 2
32°FMay 21May 17May 13May 8May 5May 2Apr 29Apr 25Apr 21
28°FMay 13May 5Apr 30Apr 27Apr 23Apr 20Apr 17Apr 13Apr 7
24°FApr 27Apr 21Apr 16Apr 13Apr 10Apr 7Apr 4Apr 2Mar 29
20°FApr 15Apr 9Apr 6Apr 4Apr 2Mar 31Mar 28Mar 24Mar 19
16°FApr 6Apr 3Mar 31Mar 28Mar 25Mar 22Mar 19Mar 16Mar 12

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 20Sep 25Sep 29Oct 1Oct 4Oct 7Oct 10Oct 14Oct 19
32°FSep 30Oct 5Oct 10Oct 14Oct 17Oct 20Oct 23Oct 27Nov 1
28°FOct 15Oct 21Oct 25Oct 28Oct 31Nov 1Nov 5Nov 9Nov 15
24°FOct 30Nov 3Nov 6Nov 10Nov 12Nov 14Nov 17Nov 22Nov 27
20°FNov 9Nov 13Nov 16Nov 19Nov 22Nov 25Nov 28Dec 1Dec 6
16°FNov 16Nov 21Nov 25Nov 29Dec 1Dec 4Dec 9Dec 14Dec 19

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°F161154149144141136131127120
32°F184178172167163159154148142
28°F211204198194190185181175165
24°F235228223218215211207202195
20°F254247242238234230226222215
16°F273266260256251247243238230

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
7,877
Cooling degree days, base 65°F
336
Growing degree days, base 40°F
3,787
Growing degree days, base 45°F
2,823
Growing degree days, base 50°F
2,001
Growing degree days, base 55°F
1,304
Growing degree days, base 60°F
738

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,38700
February1,24200
March1,12201
April743015
May4117128
June13151373
July32133566
August42108532
September19034306
October538375
November85705
December1,18300

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 2.5 km from Alpena 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 USW00014814 (Alpena Wwtp). Public domain.