Chatham climate

Chatham Frost Dates and Growing Season

NOAA 1991-2020 normals for Calhoun Rsch Stn, 24.9 km from Chatham, elevation 120 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Calhoun Rsch Stn. 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 28 and the first fall freeze around November 5, a growing season of about 224 days.

Median at 36°F
last April 8, first October 26
Median at 32°F
last March 28, first November 5
Median at 28°F
last March 10, first November 18

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 26Apr 20Apr 16Apr 12Apr 8Apr 5Apr 2Mar 29Mar 21
32°FApr 14Apr 8Apr 4Mar 31Mar 28Mar 23Mar 17Mar 12Mar 4
28°FApr 1Mar 27Mar 21Mar 15Mar 10Mar 6Mar 1Feb 25Feb 17
24°FMar 16Mar 9Mar 3Feb 28Feb 23Feb 17Feb 10Feb 3Jan 25
20°FMar 7Feb 26Feb 17Feb 8Feb 2Jan 29Jan 22Jan 11Dec 31
16°FFeb 24Feb 8Feb 1Jan 28Jan 21Jan 14Jan 7Jan 1Dec 24

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 13Oct 18Oct 21Oct 24Oct 26Oct 29Oct 31Nov 3Nov 8
32°FOct 24Oct 28Oct 31Nov 2Nov 5Nov 7Nov 11Nov 16Nov 23
28°FNov 1Nov 5Nov 9Nov 13Nov 18Nov 22Nov 26Dec 1Dec 5
24°FNov 9Nov 17Nov 23Nov 27Dec 1Dec 4Dec 9Dec 18Jan 1
20°FNov 26Dec 2Dec 7Dec 13Dec 22Dec 29Jan 2Jan 9Jan 20
16°FDec 6Dec 17Dec 25Jan 1Jan 3Jan 7Jan 13Jan 21Feb 4

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°F224215208204200195190186180
32°F248240234229224219213207200
28°F280269262256250246240233222
24°F318306297290283276269261251
20°F360345336329321312305296283
16°F365365365365356349340330313

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
92% of years
16°F or colder
62% 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
2,590
Cooling degree days, base 65°F
2,178
Growing degree days, base 40°F
8,850
Growing degree days, base 45°F
7,222
Growing degree days, base 50°F
5,729
Growing degree days, base 55°F
4,386
Growing degree days, base 60°F
3,195

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January629362
February472489
March30019232
April12470402
May22219662
June0405855
July0515980
August0505970
September7328771
October12191443
November34814182
December567583

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 24.9 km from Chatham. 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 USC00161411 (Calhoun Rsch Stn). Public domain.