Afton climate

Afton Frost Dates and Growing Season

NOAA 1991-2020 normals for Spavinaw, 35 km from Afton, elevation 685 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Spavinaw. 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 April 7 and the first fall freeze around November 2, a growing season of about 209 days.

Median at 36°F
last April 18, first October 25
Median at 32°F
last April 7, first November 2
Median at 28°F
last March 29, first November 10

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 2Apr 28Apr 25Apr 22Apr 18Apr 15Apr 12Apr 8Apr 4
32°FApr 24Apr 18Apr 14Apr 10Apr 7Apr 4Apr 1Mar 29Mar 22
28°FApr 12Apr 7Apr 3Mar 31Mar 29Mar 25Mar 21Mar 15Mar 8
24°FApr 4Mar 30Mar 25Mar 21Mar 16Mar 12Mar 7Mar 3Feb 26
20°FMar 26Mar 17Mar 13Mar 9Mar 5Mar 1Feb 26Feb 21Feb 14
16°FMar 15Mar 9Mar 5Mar 1Feb 25Feb 19Feb 15Feb 7Jan 29

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°FOct 10Oct 15Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 6
32°FOct 19Oct 24Oct 28Oct 31Nov 2Nov 4Nov 7Nov 11Nov 17
28°FOct 27Nov 1Nov 4Nov 7Nov 10Nov 13Nov 18Nov 22Nov 29
24°FNov 4Nov 9Nov 13Nov 17Nov 21Nov 25Nov 30Dec 3Dec 7
20°FNov 11Nov 18Nov 23Nov 28Dec 1Dec 4Dec 8Dec 14Dec 22
16°FNov 22Nov 28Dec 2Dec 7Dec 13Dec 19Dec 25Dec 31Jan 8

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°F209201197192188184181176168
32°F229222217213209204200195187
28°F251243237231228223219213206
24°F276266260254248242237230222
20°F299290283276271266260253242
16°F323314306298293287280272263

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
3,685
Cooling degree days, base 65°F
1,816
Growing degree days, base 40°F
7,702
Growing degree days, base 45°F
6,233
Growing degree days, base 50°F
4,909
Growing degree days, base 55°F
3,735
Growing degree days, base 60°F
2,701

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January863014
February660134
March4756125
April21836295
May55143554
June2345793
July0501966
August0471936
September20243674
October16864377
November4665115
December760027

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 35 km from Afton. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00348380 (Spavinaw). Public domain.