Swain County climate

Swain County Frost Dates and Growing Season

NOAA 1991-2020 normals for Bryson City 4, 5.3 km from Swain County, elevation 1985 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bryson City 4. 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 16 and the first fall freeze around October 24, a growing season of about 189 days.

Median at 36°F
last April 30, first October 16
Median at 32°F
last April 16, first October 24
Median at 28°F
last April 3, first November 2

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 15May 9May 6May 2Apr 30Apr 27Apr 23Apr 20Apr 15
32°FMay 2Apr 27Apr 23Apr 19Apr 16Apr 13Apr 9Apr 6Apr 1
28°FApr 19Apr 13Apr 9Apr 6Apr 3Mar 31Mar 28Mar 24Mar 17
24°FApr 6Apr 1Mar 28Mar 24Mar 20Mar 16Mar 12Mar 6Feb 28
20°FMar 26Mar 19Mar 14Mar 9Mar 4Feb 28Feb 23Feb 16Feb 5
16°FMar 16Mar 7Feb 28Feb 22Feb 15Feb 9Feb 3Jan 27Jan 16

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

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°F188182177173169165161156150
32°F210204198193189185181176170
28°F237229223218214209204198192
24°F271259252247241237232226217
20°F306294286279273267259251242
16°F340329320312305298290281268

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
4,173
Cooling degree days, base 65°F
838
Growing degree days, base 40°F
6,235
Growing degree days, base 45°F
4,804
Growing degree days, base 50°F
3,552
Growing degree days, base 55°F
2,491
Growing degree days, base 60°F
1,588

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January87209
February696016
March558073
April2979201
May11351408
June9156597
July1258722
August1236700
September42111520
October26716238
November538155
December780014

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 5.3 km from Swain 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 USC00311165 (Bryson City 4). Public domain.