Union County climate

Union County Frost Dates and Growing Season

NOAA 1991-2020 normals for Anna 2 Nne, 2.2 km from Union County, elevation 640 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Anna 2 Nne. 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 8 and the first fall freeze around October 29, a growing season of about 203 days.

Median at 36°F
last April 21, first October 19
Median at 32°F
last April 8, first October 29
Median at 28°F
last March 29, first November 8

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 6May 1Apr 27Apr 24Apr 21Apr 18Apr 15Apr 10Apr 4
32°FApr 26Apr 20Apr 16Apr 12Apr 8Apr 4Mar 31Mar 29Mar 22
28°FApr 16Apr 8Apr 4Apr 1Mar 29Mar 25Mar 21Mar 17Mar 10
24°FApr 4Mar 29Mar 23Mar 18Mar 15Mar 11Mar 7Mar 2Feb 25
20°FMar 24Mar 17Mar 12Mar 8Mar 4Mar 1Feb 25Feb 19Feb 11
16°FMar 12Mar 6Mar 2Feb 26Feb 21Feb 16Feb 10Feb 4Jan 30

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 6Oct 11Oct 14Oct 16Oct 19Oct 21Oct 24Oct 27Oct 31
32°FOct 17Oct 21Oct 24Oct 27Oct 29Oct 31Nov 2Nov 5Nov 10
28°FOct 27Nov 1Nov 3Nov 5Nov 8Nov 11Nov 14Nov 19Nov 25
24°FNov 4Nov 8Nov 12Nov 15Nov 19Nov 24Nov 28Dec 2Dec 7
20°FNov 10Nov 16Nov 22Nov 26Dec 1Dec 4Dec 8Dec 13Dec 21
16°FNov 23Nov 30Dec 4Dec 8Dec 13Dec 18Dec 23Dec 27Jan 3

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°F201194189185181177173168162
32°F225218212207203199194188182
28°F249240234229225221216211203
24°F274265260254249242236230223
20°F301291284277272266260253243
16°F326315308302296290284276266

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
3,977
Cooling degree days, base 65°F
1,634
Growing degree days, base 40°F
7,328
Growing degree days, base 45°F
5,903
Growing degree days, base 50°F
4,627
Growing degree days, base 55°F
3,489
Growing degree days, base 60°F
2,487

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January921014
February713023
March5067113
April22441293
May63142544
June3329775
July0440905
August1410874
September24214640
October19947329
November514491
December811024

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 2.2 km from Union 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 USC00110187 (Anna 2 Nne). Public domain.