Suwanee climate

Suwanee Frost Dates and Growing Season

NOAA 1991-2020 normals for Cumming 2N, 20.3 km from Suwanee, elevation 1140 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cumming 2N. 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 4 and the first fall freeze around November 4, a growing season of about 214 days.

Median at 36°F
last April 16, first October 25
Median at 32°F
last April 4, first November 4
Median at 28°F
last March 20, first November 15

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 30Apr 25Apr 21Apr 18Apr 16Apr 13Apr 9Apr 6Apr 1
32°FApr 19Apr 14Apr 10Apr 7Apr 4Apr 1Mar 29Mar 23Mar 16
28°FApr 7Apr 1Mar 28Mar 24Mar 20Mar 16Mar 11Mar 3Feb 26
24°FMar 26Mar 18Mar 12Mar 6Mar 1Feb 26Feb 20Feb 13Feb 4
20°FMar 11Mar 3Feb 26Feb 18Feb 11Feb 6Jan 31Jan 27Jan 15
16°FMar 3Feb 21Feb 10Feb 4Jan 31Jan 27Jan 19Jan 12Jan 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 11Oct 16Oct 20Oct 23Oct 25Oct 27Oct 30Nov 2Nov 7
32°FOct 23Oct 27Oct 30Nov 1Nov 4Nov 6Nov 9Nov 14Nov 23
28°FNov 1Nov 5Nov 8Nov 12Nov 15Nov 20Nov 25Dec 1Dec 5
24°FNov 9Nov 15Nov 22Nov 28Dec 1Dec 5Dec 10Dec 19Dec 30
20°FNov 24Dec 2Dec 7Dec 14Dec 23Dec 30Jan 2Jan 9Jan 17
16°FDec 11Dec 21Dec 28Jan 1Jan 6Jan 11Jan 16Jan 24Feb 2

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°F212205200196191187183177171
32°F241230223218214209205201194
28°F272261254248243237231225216
24°F309298290282275268261254242
20°F342331323315308301294285274
16°F365364353343336331324314302

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
97% of years
16°F or colder
82% 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
3,241
Cooling degree days, base 65°F
1,480
Growing degree days, base 40°F
7,578
Growing degree days, base 45°F
6,022
Growing degree days, base 50°F
4,626
Growing degree days, base 55°F
3,405
Growing degree days, base 60°F
2,361

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January739028
February572040
March4254132
April20026291
May51125540
June2290738
July0406871
August0386851
September15200635
October16341350
November4263107
December648044

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 20.3 km from Suwanee. 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 USC00092408 (Cumming 2N). Public domain.