Green Valley climate

Green Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Green Valley, 4.4 km from Green Valley, elevation 2900 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Green Valley. 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 November 27, a growing season of about 276 days.

Median at 36°F
last March 15, first November 16
Median at 32°F
last February 25, first November 27
Median at 28°F
last February 1, first December 10

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 7Mar 31Mar 25Mar 19Mar 15Mar 11Mar 6Mar 3Feb 24
32°FMar 18Mar 9Mar 4Feb 28Feb 25Feb 19Feb 13Feb 7Jan 31
28°FFeb 27Feb 17Feb 10Feb 5Feb 1Jan 28Jan 20Jan 12Jan 2
24°FFeb 7Feb 1Jan 26Jan 16Jan 10Jan 3Dec 30Dec 23Dec 13
20°FFeb 4Jan 28Jan 16Jan 11Jan 7Jan 3Dec 31Dec 26Dec 12
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°FNov 1Nov 5Nov 10Nov 13Nov 16Nov 19Nov 22Nov 26Dec 2
32°FNov 12Nov 17Nov 20Nov 24Nov 27Dec 1Dec 4Dec 7Dec 13
28°FNov 22Nov 28Dec 3Dec 7Dec 10Dec 14Dec 19Dec 25Jan 5
24°FDec 3Dec 11Dec 15Dec 21Dec 26Dec 31Jan 6Jan 15Jan 29
20°FDec 12Dec 22Dec 30Jan 1Jan 5Jan 9Jan 14Jan 21Feb 1
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°F269260254249243237232224216
32°F305295289282276270264256248
28°F346335329322316308300290280
24°F365365365360353346339331320
20°F365365365365365365365365359
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
99% of years
24°F or colder
67% of years
20°F or colder
14% of years
16°F or colder
0% 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
1,631
Cooling degree days, base 65°F
2,909
Growing degree days, base 40°F
10,415
Growing degree days, base 45°F
8,634
Growing degree days, base 50°F
6,939
Growing degree days, base 55°F
5,399
Growing degree days, base 60°F
4,055

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January4190106
February3073150
March18227319
April6596483
May8303760
June05641,014
July06341,099
August05951,060
September0462912
October27194633
November19530299
December4281105

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 4.4 km from Green Valley. 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 USC00023668 (Green Valley). Public domain.