Chatham County climate

Chatham County Frost Dates and Growing Season

NOAA 1991-2020 normals for Siler City 2 N, 19.8 km from Chatham County, elevation 610 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Siler City 2 N. 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 31 and the first fall freeze around November 4, a growing season of about 220 days.

Median at 36°F
last April 13, first October 27
Median at 32°F
last March 31, first November 4
Median at 28°F
last March 17, first November 16

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 29Apr 23Apr 19Apr 16Apr 13Apr 10Apr 6Apr 3Mar 29
32°FApr 13Apr 9Apr 5Apr 2Mar 31Mar 27Mar 24Mar 19Mar 14
28°FApr 3Mar 30Mar 25Mar 20Mar 17Mar 14Mar 10Mar 6Feb 27
24°FMar 23Mar 17Mar 12Mar 8Mar 4Feb 28Feb 25Feb 18Feb 8
20°FMar 12Mar 4Feb 28Feb 23Feb 15Feb 8Feb 4Jan 31Jan 20
16°FMar 2Feb 20Feb 10Feb 4Jan 31Jan 28Jan 21Jan 15Jan 3

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 15Oct 19Oct 22Oct 25Oct 27Oct 30Nov 1Nov 3Nov 7
32°FOct 23Oct 28Oct 31Nov 2Nov 4Nov 7Nov 10Nov 13Nov 20
28°FNov 3Nov 6Nov 10Nov 13Nov 16Nov 20Nov 26Dec 1Dec 8
24°FNov 11Nov 16Nov 22Nov 26Dec 1Dec 4Dec 9Dec 18Dec 28
20°FNov 28Dec 2Dec 10Dec 18Dec 26Jan 1Jan 3Jan 9Jan 17
16°FDec 12Dec 23Dec 29Jan 1Jan 7Jan 11Jan 16Jan 22Feb 1

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°F216209204199196193188183175
32°F242234228224220216211207200
28°F273263255249245240235229221
24°F306294286278272266260253242
20°F341330321313306300293285275
16°F365362350342335330321312301

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
98% of years
16°F or colder
83% 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
3,504
Cooling degree days, base 65°F
1,498
Growing degree days, base 40°F
7,418
Growing degree days, base 45°F
5,912
Growing degree days, base 50°F
4,563
Growing degree days, base 55°F
3,373
Growing degree days, base 60°F
2,353

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January775028
February611140
March4647128
April21739293
May64126528
June6298742
July0422887
August0369834
September23194621
October20037316
November4614106
December682142

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 19.8 km from Chatham 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 USC00317924 (Siler City 2 N). Public domain.