Decatur climate

Decatur Frost Dates and Growing Season

NOAA 1991-2020 normals for Decatur 7NE, 17.9 km from Decatur, elevation 750 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Decatur 7NE. 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 10 and the first fall freeze around October 27, a growing season of about 199 days.

Median at 36°F
last April 24, first October 19
Median at 32°F
last April 10, first October 27
Median at 28°F
last March 30, first November 5

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 9May 4Apr 30Apr 27Apr 24Apr 21Apr 17Apr 13Apr 7
32°FApr 28Apr 22Apr 18Apr 14Apr 10Apr 7Apr 3Mar 31Mar 24
28°FApr 16Apr 9Apr 5Apr 1Mar 30Mar 26Mar 22Mar 16Mar 8
24°FApr 3Mar 30Mar 25Mar 19Mar 15Mar 12Mar 7Feb 28Feb 22
20°FMar 25Mar 17Mar 13Mar 7Feb 28Feb 25Feb 18Feb 10Feb 1
16°FMar 15Mar 6Feb 27Feb 19Feb 11Feb 4Jan 31Jan 24Jan 11

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 8Oct 11Oct 14Oct 17Oct 19Oct 22Oct 24Oct 27Oct 31
32°FOct 14Oct 18Oct 22Oct 25Oct 27Oct 30Nov 1Nov 4Nov 9
28°FOct 24Oct 29Nov 1Nov 2Nov 5Nov 8Nov 11Nov 15Nov 21
24°FNov 1Nov 6Nov 10Nov 14Nov 17Nov 21Nov 25Nov 30Dec 6
20°FNov 12Nov 19Nov 24Nov 29Dec 2Dec 7Dec 13Dec 22Jan 1
16°FNov 26Dec 2Dec 8Dec 16Dec 24Dec 30Jan 2Jan 8Jan 18

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°F197191186182178174170164158
32°F221212207203199194190184177
28°F245235229224220216211206198
24°F275265258253247241235228222
20°F314302293285278271264256247
16°F347336329322312306297288275

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
96% 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
3,840
Cooling degree days, base 65°F
1,450
Growing degree days, base 40°F
7,135
Growing degree days, base 45°F
5,680
Growing degree days, base 50°F
4,386
Growing degree days, base 55°F
3,260
Growing degree days, base 60°F
2,285

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January840021
February660026
March508294
April24821254
May70114510
June3282729
July0405869
August0378843
September21210639
October21636306
November523169
December752027

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 17.9 km from Decatur. 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 USC00402388 (Decatur 7NE). Public domain.