Durham climate

Durham Frost Dates and Growing Season

NOAA 1991-2020 normals for Portland Kgw-TV, 13.8 km from Durham, elevation 159 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Portland Kgw-TV. 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 25 and the first fall freeze around December 1, a growing season of about 280 days.

Median at 36°F
last March 29, first November 12
Median at 32°F
last February 25, first December 1
Median at 28°F
last January 31, first December 20

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 21Apr 13Apr 5Apr 1Mar 29Mar 25Mar 20Mar 14Mar 7
32°FMar 21Mar 13Mar 6Feb 28Feb 25Feb 18Feb 11Feb 3Jan 24
28°FFeb 26Feb 18Feb 10Feb 4Jan 31Jan 23Jan 14Jan 3Dec 21
24°FFeb 18Feb 9Feb 1Jan 26Jan 15Jan 6Dec 29Dec 20Dec 8
20°FFeb 18Feb 5Feb 1Jan 25Jan 13Jan 1Dec 24Dec 19Dec 7
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°FOct 28Nov 2Nov 6Nov 10Nov 12Nov 16Nov 21Nov 25Dec 1
32°FNov 10Nov 16Nov 22Nov 26Dec 1Dec 5Dec 11Dec 18Dec 27
28°FNov 25Dec 2Dec 7Dec 13Dec 20Dec 27Jan 3Jan 13Jan 30
24°FNov 30Dec 7Dec 15Dec 22Dec 29Jan 6Jan 16Jan 30Feb 11
20°FDec 6Dec 14Dec 21Dec 28Jan 6Jan 16Jan 29Feb 3Feb 14
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°F258248238232227222216209200
32°F318305295287280272265257245
28°F365354344334329320313306292
24°F365365365365363353344332319
20°F365365365365365365365365342
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
100% of years
28°F or colder
86% of years
24°F or colder
49% of years
20°F or colder
19% of years
16°F or colder
5% 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
4,167
Cooling degree days, base 65°F
448
Growing degree days, base 40°F
5,532
Growing degree days, base 45°F
3,969
Growing degree days, base 50°F
2,697
Growing degree days, base 55°F
1,713
Growing degree days, base 60°F
966

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January71005
February570012
March516042
April3803105
May21721274
June10548393
July18145592
August13156608
September7070450
October3024183
November542029
December72505

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 13.8 km from Durham. 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 USC00356749 (Portland Kgw-TV). Public domain.