Deer Valley Frost Dates and Growing Season

NOAA 1991-2020 normals for Phoenix Deer Valley Muni AP, 5 km from Deer Valley, elevation 1455 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Phoenix Deer Valley Muni AP. 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 January 8 and the first fall freeze around December 25, a growing season of about 354 days.

Median at 36°F: last February 1, first December 11
Median at 32°F: last January 8, first December 25
Median at 28°F: last January 8, first January 7

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Mar 2	Feb 21	Feb 13	Feb 7	Feb 1	Jan 24	Jan 17	Jan 10	Jan 1
32°F	Feb 12	Feb 1	Jan 23	Jan 14	Jan 8	Jan 2	Dec 31	Dec 24	Dec 16
28°F	Feb 2	Jan 24	Jan 19	Jan 12	Jan 8	Jan 4	Jan 1	Dec 29	Dec 15
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	Nov 25	Dec 1	Dec 5	Dec 8	Dec 11	Dec 15	Dec 18	Dec 23	Dec 29
32°F	Dec 5	Dec 11	Dec 15	Dec 20	Dec 25	Dec 29	Jan 2	Jan 9	Jan 23
28°F	Dec 14	Dec 27	Dec 31	Jan 3	Jan 7	Jan 11	Jan 17	Jan 23	Feb 1
24°F	–	–	–	–	–	–	–	–	–
20°F	–	–	–	–	–	–	–	–	–
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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	347	337	329	321	314	307	299	290	279
32°F	365	365	365	360	354	347	341	332	320
28°F	365	365	365	365	365	365	365	365	359
24°F	365	365	365	365	365	365	365	365	365
20°F	365	365	365	365	365	365	365	365	365
16°F	365	365	365	365	365	365	365	365	365

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder: 99% of years
32°F or colder: 70% of years
28°F or colder: 17% of years
24°F or colder: 2% of years
20°F or colder: 0% 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: 1,202
Cooling degree days, base 65°F: 3,963
Growing degree days, base 40°F: 11,887
Growing degree days, base 45°F: 10,073
Growing degree days, base 50°F: 8,306
Growing degree days, base 55°F: 6,665
Growing degree days, base 60°F: 5,212

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	319	1	171
February	226	5	210
March	117	54	403
April	29	165	587
May	3	409	871
June	0	663	1,113
July	0	849	1,314
August	0	821	1,286
September	0	633	1,083
October	10	305	760
November	135	57	375
December	363	1	133

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 km from Deer Valley. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00003184 (Phoenix Deer Valley Muni AP). Public domain.