DeKalb County climate

DeKalb County Frost Dates and Growing Season

NOAA 1991-2020 normals for Smithville 2 Se, 5.8 km from DeKalb County, elevation 890 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Smithville 2 Se. 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 18 and the first fall freeze around October 22, a growing season of about 187 days.

Median at 36°F
last April 30, first October 13
Median at 32°F
last April 18, first October 22
Median at 28°F
last April 4, first November 1

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 14May 9May 5May 2Apr 30Apr 27Apr 24Apr 20Apr 16
32°FMay 2Apr 28Apr 23Apr 21Apr 18Apr 14Apr 11Apr 8Apr 2
28°FApr 20Apr 14Apr 10Apr 7Apr 4Apr 1Mar 28Mar 24Mar 18
24°FApr 7Apr 3Mar 31Mar 27Mar 24Mar 20Mar 15Mar 10Mar 3
20°FMar 29Mar 22Mar 16Mar 13Mar 8Mar 4Feb 28Feb 22Feb 14
16°FMar 16Mar 9Mar 3Feb 27Feb 21Feb 16Feb 10Feb 3Jan 26

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 1Oct 6Oct 9Oct 11Oct 13Oct 16Oct 19Oct 22Oct 26
32°FOct 10Oct 15Oct 17Oct 20Oct 22Oct 25Oct 27Oct 31Nov 4
28°FOct 19Oct 22Oct 26Oct 29Nov 1Nov 2Nov 5Nov 8Nov 13
24°FOct 28Nov 1Nov 4Nov 7Nov 10Nov 13Nov 17Nov 22Nov 29
20°FNov 5Nov 11Nov 15Nov 20Nov 24Nov 28Dec 2Dec 6Dec 16
16°FNov 18Nov 25Dec 1Dec 5Dec 10Dec 17Dec 23Dec 29Jan 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°F185178174170167163159154149
32°F207200195191187183179174167
28°F230222216212209205201196190
24°F257249243237232227221216209
20°F291278271266260255249243233
16°F327316307300293286279270260

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
4,148
Cooling degree days, base 65°F
1,231
Growing degree days, base 40°F
6,748
Growing degree days, base 45°F
5,330
Growing degree days, base 50°F
4,066
Growing degree days, base 55°F
2,967
Growing degree days, base 60°F
2,025

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January888017
February705023
March548286
April27816229
May8895473
June7248691
July0360825
August1324787
September38160572
October25625266
November552271
December786027

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 5.8 km from DeKalb County. 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 USC00408405 (Smithville 2 Se). Public domain.