Union County climate

Union County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hickory Flat, 22.3 km from Union County, elevation 400 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hickory Flat. 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 28, a growing season of about 202 days.

Median at 36°F
last April 20, first October 20
Median at 32°F
last April 8, first October 28
Median at 28°F
last March 28, 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 3Apr 29Apr 26Apr 22Apr 20Apr 16Apr 13Apr 10Apr 5
32°FApr 25Apr 19Apr 14Apr 11Apr 8Apr 5Apr 2Mar 29Mar 22
28°FApr 12Apr 7Apr 4Mar 31Mar 28Mar 25Mar 21Mar 15Mar 8
24°FApr 2Mar 28Mar 23Mar 18Mar 14Mar 9Mar 5Feb 28Feb 22
20°FMar 20Mar 14Mar 8Mar 4Feb 28Feb 26Feb 20Feb 14Feb 3
16°FMar 12Mar 4Feb 27Feb 20Feb 15Feb 9Feb 2Jan 27Jan 17

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 5Oct 11Oct 14Oct 17Oct 20Oct 22Oct 24Oct 27Oct 31
32°FOct 14Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 11
28°FOct 24Oct 29Nov 1Nov 3Nov 5Nov 9Nov 13Nov 18Nov 24
24°FNov 2Nov 5Nov 9Nov 13Nov 17Nov 21Nov 26Dec 1Dec 6
20°FNov 9Nov 15Nov 21Nov 26Dec 1Dec 3Dec 8Dec 16Dec 28
16°FNov 20Dec 1Dec 6Dec 12Dec 20Dec 28Jan 1Jan 8Jan 16

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°F203195191187183179175170163
32°F224216210206202198194188180
28°F248240233228223219214209201
24°F274264258253247242237231223
20°F305294286280274269262255246
16°F337327318311304298290282271

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
98% 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
3,511
Cooling degree days, base 65°F
1,650
Growing degree days, base 40°F
7,626
Growing degree days, base 45°F
6,135
Growing degree days, base 50°F
4,788
Growing degree days, base 55°F
3,589
Growing degree days, base 60°F
2,543

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January800127
February632140
March4507135
April19839310
May51148563
June1328777
July0428893
August0411876
September17229661
October17954355
November4714108
December711143

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 22.3 km from Union County. 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 USC00224001 (Hickory Flat). Public domain.