Yarnell climate

Yarnell Frost Dates and Growing Season

NOAA 1991-2020 normals for Wickenburg, 27 km from Yarnell, elevation 2095 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wickenburg. 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 March 7 and the first fall freeze around November 20, a growing season of about 254 days.

Median at 36°F
last April 3, first November 9
Median at 32°F
last March 7, first November 20
Median at 28°F
last February 14, first December 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°FApr 25Apr 18Apr 11Apr 6Apr 3Mar 30Mar 24Mar 17Mar 11
32°FApr 8Mar 30Mar 18Mar 12Mar 7Mar 3Feb 27Feb 22Feb 14
28°FMar 6Mar 1Feb 24Feb 19Feb 14Feb 9Feb 4Jan 27Jan 15
24°FFeb 22Feb 12Feb 5Jan 29Jan 20Jan 11Jan 4Dec 29Dec 19
20°FFeb 11Jan 31Jan 19Jan 11Jan 4Dec 31Dec 27Dec 21Dec 11
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 24Oct 31Nov 3Nov 6Nov 9Nov 12Nov 15Nov 18Nov 22
32°FNov 4Nov 9Nov 14Nov 17Nov 20Nov 23Nov 27Dec 1Dec 5
28°FNov 14Nov 21Nov 25Nov 29Dec 2Dec 6Dec 10Dec 15Dec 22
24°FNov 27Dec 2Dec 6Dec 11Dec 15Dec 20Dec 25Dec 31Jan 12
20°FDec 7Dec 14Dec 21Dec 26Dec 29Jan 1Jan 7Jan 17Jan 31
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°F245237230224219214208201191
32°F282273266260254249241233223
28°F325311303296290284279272261
24°F365355346339333325316306297
20°F365365365365365365359348337
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
100% of years
24°F or colder
91% of years
20°F or colder
40% of years
16°F or colder
4% 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
1,985
Cooling degree days, base 65°F
2,807
Growing degree days, base 40°F
9,958
Growing degree days, base 45°F
8,183
Growing degree days, base 50°F
6,532
Growing degree days, base 55°F
5,078
Growing degree days, base 60°F
3,844

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January474066
February358099
March22911257
April9255414
May16232681
June0488938
July07241,189
August06901,155
September0459909
October42143566
November2628214
December510047

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 27 km from Yarnell. 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 USC00029287 (Wickenburg). Public domain.