Encanto Frost Dates and Growing Season

NOAA 1991-2020 normals for South Phoenix, 10.9 km from Encanto, elevation 1155 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for South Phoenix. 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 21 and the first fall freeze around December 16, a growing season of about 331 days.

Median at 36°F: last February 15, first December 1
Median at 32°F: last January 21, first December 16
Median at 28°F: last January 3, first December 29

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 7	Mar 1	Feb 27	Feb 20	Feb 15	Feb 10	Feb 3	Jan 28	Jan 16
32°F	Feb 20	Feb 11	Feb 3	Jan 29	Jan 21	Jan 14	Jan 7	Jan 2	Dec 24
28°F	Feb 8	Jan 26	Jan 15	Jan 8	Jan 3	Dec 31	Dec 28	Dec 21	Dec 13
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 16	Nov 22	Nov 25	Nov 29	Dec 1	Dec 5	Dec 8	Dec 12	Dec 17
32°F	Nov 29	Dec 4	Dec 8	Dec 12	Dec 16	Dec 20	Dec 25	Dec 30	Jan 9
28°F	Dec 10	Dec 14	Dec 19	Dec 25	Dec 29	Jan 1	Jan 5	Jan 14	Jan 28
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	322	309	302	296	289	283	278	271	263
32°F	358	351	343	336	331	323	316	307	295
28°F	365	365	365	365	365	363	356	346	334
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: 100% of years
32°F or colder: 94% of years
28°F or colder: 47% of years
24°F or colder: 4% 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: 1,228
Cooling degree days, base 65°F: 3,579
Growing degree days, base 40°F: 11,477
Growing degree days, base 45°F: 9,658
Growing degree days, base 50°F: 7,882
Growing degree days, base 55°F: 6,241
Growing degree days, base 60°F: 4,804

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	332	1	152
February	213	5	215
March	112	50	404
April	27	159	582
May	2	374	837
June	0	603	1,053
July	0	770	1,235
August	0	753	1,218
September	0	574	1,024
October	13	260	711
November	152	30	332
December	377	0	118

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 10.9 km from Encanto. 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 USC00028112 (South Phoenix). Public domain.