Saint Simons Island climate

Saint Simons Island Frost Dates and Growing Season

NOAA 1991-2020 normals for Brunswick Malcolm Mckinnon AP, 2.1 km from Saint Simons Island, elevation 16 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Brunswick Malcolm Mckinnon AP. 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 February 9 and the first fall freeze around December 26, a growing season of about 312 days.

Median at 36°F
last February 27, first December 4
Median at 32°F
last February 9, first December 26
Median at 28°F
last January 27, first January 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°FMar 18Mar 11Mar 6Mar 3Feb 27Feb 23Feb 17Feb 10Feb 1
32°FMar 6Feb 28Feb 23Feb 15Feb 9Feb 4Jan 30Jan 21Jan 11
28°FFeb 26Feb 14Feb 6Jan 31Jan 27Jan 20Jan 14Jan 8Dec 30
24°FFeb 14Feb 4Jan 30Jan 25Jan 18Jan 13Jan 8Jan 3Dec 28
20°F–––––––––
16°F–––––––––

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°FNov 16Nov 22Nov 27Dec 1Dec 4Dec 8Dec 15Dec 22Jan 1
32°FNov 30Dec 6Dec 13Dec 20Dec 26Dec 31Jan 4Jan 9Jan 19
28°FDec 13Dec 24Dec 30Jan 3Jan 8Jan 13Jan 18Jan 27Feb 7
24°FDec 21Jan 1Jan 4Jan 8Jan 13Jan 19Jan 26Jan 31Feb 7
20°F–––––––––
16°F–––––––––

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°F312302295288282276270263251
32°F346334326319312306299291279
28°F365365357348341334329320308
24°F365365365365365365357343331
20°F365365365365365365365365365
16°F365365365365365365365365365

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
98% of years
28°F or colder
74% of years
24°F or colder
35% of years
20°F or colder
7% of years
16°F or colder
0% 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
1,308
Cooling degree days, base 65°F
2,848
Growing degree days, base 40°F
10,677
Growing degree days, base 45°F
8,891
Growing degree days, base 50°F
7,170
Growing degree days, base 55°F
5,566
Growing degree days, base 60°F
4,116

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January3806161
February26312200
March15248370
April42132540
May3333795
June0479929
July05751,040
August05501,015
September0425874
October23218660
November14555367
December30215218

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 2.1 km from Saint Simons Island. 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 USW00013878 (Brunswick Malcolm Mckinnon AP). Public domain.