Duncan climate

Duncan Frost Dates and Growing Season

NOAA 1991-2020 normals for Duncan, 3.3 km from Duncan, elevation 3660 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Duncan. 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 24 and the first fall freeze around October 25, a growing season of about 183 days.

Median at 36°F
last May 5, first October 17
Median at 32°F
last April 24, first October 25
Median at 28°F
last April 7, 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 18May 14May 10May 7May 5May 2Apr 30Apr 27Apr 22
32°FMay 8May 3Apr 30Apr 27Apr 24Apr 21Apr 18Apr 13Apr 8
28°FApr 27Apr 20Apr 14Apr 10Apr 7Apr 3Mar 30Mar 24Mar 16
24°FApr 7Apr 1Mar 27Mar 20Mar 15Mar 12Mar 7Mar 3Feb 26
20°FMar 15Mar 9Mar 5Mar 1Feb 27Feb 22Feb 16Feb 10Feb 1
16°FMar 3Feb 25Feb 18Feb 12Feb 6Feb 2Jan 28Jan 20Jan 5

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 4Oct 8Oct 11Oct 14Oct 17Oct 19Oct 21Oct 25Oct 29
32°FOct 11Oct 16Oct 19Oct 22Oct 25Oct 28Oct 31Nov 1Nov 5
28°FOct 20Oct 24Oct 28Oct 31Nov 2Nov 5Nov 8Nov 11Nov 15
24°FOct 27Nov 1Nov 5Nov 8Nov 12Nov 15Nov 18Nov 21Nov 26
20°FNov 4Nov 10Nov 15Nov 18Nov 21Nov 24Nov 27Dec 1Dec 7
16°FNov 15Nov 22Nov 26Nov 30Dec 3Dec 7Dec 12Dec 18Jan 1

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°F182176171168164159156151145
32°F203196191187183179174169162
28°F231223217211206202197191183
24°F263255248243238233226219210
20°F298289281275270264258251244
16°F338328318309303297289280268

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
99% 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
3,091
Cooling degree days, base 65°F
1,801
Growing degree days, base 40°F
7,926
Growing degree days, base 45°F
6,317
Growing degree days, base 50°F
4,911
Growing degree days, base 55°F
3,702
Growing degree days, base 60°F
2,670

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January69306
February512025
March3791122
April17915291
May37130558
June1380829
July0512977
August0467932
September4260707
October12636379
November449181
December71105

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 3.3 km from Duncan. 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 USC00022754 (Duncan). Public domain.