Pima climate

Pima Frost Dates and Growing Season

NOAA 1991-2020 normals for Safford Ag Ctr, 16.5 km from Pima, elevation 2954 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Safford Ag Ctr. 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 25 and the first fall freeze around November 9, a growing season of about 228 days.

Median at 36°F
last April 12, first October 30
Median at 32°F
last March 25, first November 9
Median at 28°F
last March 3, first November 22

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 2Apr 25Apr 20Apr 17Apr 12Apr 9Apr 6Apr 1Mar 25
32°FApr 14Apr 7Apr 3Mar 30Mar 25Mar 20Mar 15Mar 10Mar 5
28°FMar 23Mar 15Mar 10Mar 6Mar 3Feb 28Feb 22Feb 16Feb 8
24°FMar 6Feb 28Feb 23Feb 16Feb 11Feb 7Feb 2Jan 29Jan 15
20°FFeb 18Feb 8Feb 3Jan 30Jan 23Jan 16Jan 9Dec 31Dec 20
16°FFeb 9Feb 1Jan 24Jan 17Jan 11Jan 6Dec 31Dec 22Dec 12

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 14Oct 18Oct 23Oct 26Oct 30Nov 1Nov 4Nov 7Nov 13
32°FOct 23Oct 30Nov 3Nov 6Nov 9Nov 13Nov 16Nov 20Nov 25
28°FNov 3Nov 10Nov 15Nov 18Nov 22Nov 24Nov 28Dec 1Dec 6
24°FNov 16Nov 22Nov 26Nov 30Dec 3Dec 6Dec 11Dec 15Dec 23
20°FNov 28Dec 4Dec 9Dec 15Dec 20Dec 24Dec 29Jan 4Jan 16
16°FDec 6Dec 14Dec 22Dec 28Jan 1Jan 6Jan 12Jan 20Feb 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°F222213207202197193188181174
32°F253244238233228222216210201
28°F288278271265260255250243234
24°F327317308300293286279272263
20°F365357349340334328320311299
16°F365365365365365365355345333

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
90% of years
16°F or colder
42% 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
2,345
Cooling degree days, base 65°F
2,416
Growing degree days, base 40°F
9,232
Growing degree days, base 45°F
7,521
Growing degree days, base 50°F
5,967
Growing degree days, base 55°F
4,609
Growing degree days, base 60°F
3,430

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January584023
February410074
March2606228
April9464422
May14246698
June0489939
July05951,060
August05411,006
September1364813
October63105509
November3206172
December600024

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 16.5 km from Pima. 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 USC00027390 (Safford Ag Ctr). Public domain.