Marana climate

Marana Frost Dates and Growing Season

NOAA 1991-2020 normals for Tucson 17 Nw, 20.5 km from Marana, elevation 2561 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tucson 17 Nw. 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 23 and the first fall freeze around December 6, a growing season of about 287 days.

Median at 36°F
last March 15, first November 24
Median at 32°F
last February 23, first December 6
Median at 28°F
last January 22, first December 19

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 10Apr 1Mar 26Mar 20Mar 15Mar 10Mar 6Feb 28Feb 22
32°FMar 22Mar 11Mar 5Mar 1Feb 23Feb 16Feb 9Jan 31Jan 15
28°FMar 1Feb 15Feb 7Feb 1Jan 22Jan 11Jan 4Dec 30Dec 19
24°FFeb 12Feb 5Jan 31Jan 22Jan 9Jan 2Dec 29Dec 23Dec 13
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.

Threshold10%20%30%40%50%60%70%80%90%
36°FNov 7Nov 13Nov 17Nov 21Nov 24Nov 28Dec 2Dec 5Dec 10
32°FNov 18Nov 24Nov 29Dec 3Dec 6Dec 9Dec 12Dec 17Dec 25
28°FNov 30Dec 5Dec 10Dec 14Dec 19Dec 24Dec 29Jan 5Jan 22
24°FDec 10Dec 16Dec 23Dec 27Jan 1Jan 5Jan 14Jan 28Feb 3
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.

Threshold10%20%30%40%50%60%70%80%90%
36°F282271265258252246239232219
32°F324312303294287280272265254
28°F365357349340333326318306294
24°F365365365365365365356344329
20°F365365365365365365365365365
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
87% of years
24°F or colder
38% of years
20°F or colder
7% of years
16°F or colder
1% 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
1,447
Cooling degree days, base 65°F
3,316
Growing degree days, base 40°F
11,003
Growing degree days, base 45°F
9,213
Growing degree days, base 50°F
7,494
Growing degree days, base 55°F
5,910
Growing degree days, base 60°F
4,514

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January3722141
February2735178
March16338348
April55133529
May7346805
June06181,068
July07101,175
August06571,122
September0515964
October23244687
November16246345
December3922132

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 20.5 km from Marana. 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 USC00028795 (Tucson 17 Nw). Public domain.