Hartselle climate

Hartselle Frost Dates and Growing Season

NOAA 1991-2020 normals for Decatur 4SE, 14.7 km from Hartselle, elevation 550 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Decatur 4SE. 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 March 26 and the first fall freeze around November 7, a growing season of about 228 days.

Median at 36°F
last April 5, first October 29
Median at 32°F
last March 26, first November 7
Median at 28°F
last March 12, first November 19

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°FApr 22Apr 15Apr 11Apr 8Apr 5Apr 3Mar 31Mar 27Mar 21
32°FApr 9Apr 5Apr 1Mar 29Mar 26Mar 22Mar 18Mar 14Mar 5
28°FMar 30Mar 23Mar 19Mar 16Mar 12Mar 7Mar 3Feb 28Feb 21
24°FMar 18Mar 12Mar 6Mar 1Feb 26Feb 22Feb 18Feb 12Feb 4
20°FMar 6Feb 28Feb 22Feb 15Feb 10Feb 4Jan 31Jan 25Jan 15
16°FFeb 24Feb 12Feb 4Jan 31Jan 28Jan 23Jan 17Jan 10Jan 1

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 16Oct 21Oct 24Oct 26Oct 29Oct 31Nov 3Nov 6Nov 11
32°FOct 26Oct 30Nov 1Nov 4Nov 7Nov 10Nov 13Nov 18Nov 26
28°FNov 4Nov 7Nov 11Nov 15Nov 19Nov 23Nov 28Dec 3Dec 10
24°FNov 12Nov 18Nov 25Nov 30Dec 3Dec 7Dec 13Dec 22Jan 1
20°FNov 26Dec 2Dec 9Dec 16Dec 24Dec 30Jan 2Jan 9Jan 18
16°FDec 9Dec 19Dec 27Jan 1Jan 4Jan 8Jan 14Jan 20Jan 31

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°F227219213209205202198193187
32°F252244239234228223218213205
28°F279270263258253247242237228
24°F312302294287281274268261252
20°F346333326318311306299292280
16°F365364353344337332326317305

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
98% of years
16°F or colder
82% 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
3,048
Cooling degree days, base 65°F
1,754
Growing degree days, base 40°F
8,070
Growing degree days, base 45°F
6,502
Growing degree days, base 50°F
5,071
Growing degree days, base 55°F
3,792
Growing degree days, base 60°F
2,690

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January719043
February549159
March37611172
April15451355
May34161592
June0338787
July0443908
August0423888
September12259697
October14759385
November4166128
December640156

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 14.7 km from Hartselle. 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 USC00012209 (Decatur 4SE). Public domain.