Decatur climate

Decatur Frost Dates and Growing Season

NOAA 1991-2020 normals for Decatur, 3.4 km from Decatur, elevation 970 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Decatur. 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 20 and the first fall freeze around November 11, a growing season of about 237 days.

Median at 36°F
last April 3, first November 2
Median at 32°F
last March 20, first November 11
Median at 28°F
last March 6, first November 23

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 16Apr 11Apr 6Apr 3Mar 31Mar 27Mar 21Mar 15
32°FApr 11Apr 3Mar 30Mar 25Mar 20Mar 16Mar 12Mar 7Feb 28
28°FMar 26Mar 19Mar 14Mar 10Mar 6Mar 2Feb 27Feb 22Feb 15
24°FMar 14Mar 9Mar 4Feb 28Feb 24Feb 19Feb 12Feb 3Jan 26
20°FMar 6Feb 26Feb 18Feb 9Feb 3Jan 29Jan 23Jan 15Dec 31
16°FFeb 21Feb 9Feb 2Jan 29Jan 21Jan 14Jan 5Dec 29Dec 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°FOct 19Oct 24Oct 28Oct 31Nov 2Nov 5Nov 8Nov 12Nov 18
32°FOct 25Nov 1Nov 4Nov 8Nov 11Nov 15Nov 19Nov 23Nov 29
28°FNov 3Nov 9Nov 14Nov 18Nov 23Nov 28Dec 1Dec 4Dec 10
24°FNov 13Nov 22Nov 28Dec 2Dec 5Dec 9Dec 16Dec 22Dec 31
20°FNov 28Dec 3Dec 8Dec 14Dec 21Dec 28Jan 3Jan 10Jan 23
16°FDec 6Dec 12Dec 19Dec 28Jan 1Jan 7Jan 14Jan 26Feb 5

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°F239231225219214210204198191
32°F262254248243237232226220211
28°F290279272266261256250245235
24°F324310302296289282275267258
20°F363349340333325317308299287
16°F365365365364354346336329313

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
93% of years
16°F or colder
65% 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
2,534
Cooling degree days, base 65°F
2,551
Growing degree days, base 40°F
9,319
Growing degree days, base 45°F
7,690
Growing degree days, base 50°F
6,182
Growing degree days, base 55°F
4,818
Growing degree days, base 60°F
3,600

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January631262
February4756102
March30027245
April11487431
May20251696
June0468918
July06121,077
August05901,055
September5356801
October92128505
November32221210
December576481

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 3.4 km from Decatur. 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 USC00412334 (Decatur). Public domain.