Tombstone climate

Tombstone Frost Dates and Growing Season

NOAA 1991-2020 normals for Tombstone, 0.1 km from Tombstone, elevation 4659 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Tombstone. 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 4 and the first fall freeze around November 29, a growing season of about 264 days.

Median at 36°F
last March 29, first November 17
Median at 32°F
last March 4, first November 29
Median at 28°F
last February 8, first December 12

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 18Apr 11Apr 5Apr 1Mar 29Mar 24Mar 19Mar 13Mar 5
32°FMar 31Mar 24Mar 16Mar 10Mar 4Feb 28Feb 23Feb 17Feb 3
28°FMar 10Feb 28Feb 21Feb 16Feb 8Feb 2Jan 27Jan 16Jan 5
24°FFeb 18Feb 8Feb 1Jan 24Jan 15Jan 7Jan 2Dec 26Dec 14
20°FFeb 7Feb 2Jan 28Jan 18Jan 11Jan 4Jan 1Dec 29Dec 19
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°FOct 31Nov 5Nov 10Nov 14Nov 17Nov 20Nov 23Nov 27Dec 3
32°FNov 12Nov 18Nov 22Nov 25Nov 29Dec 2Dec 6Dec 10Dec 17
28°FNov 23Nov 29Dec 4Dec 8Dec 12Dec 17Dec 23Dec 31Jan 10
24°FDec 3Dec 11Dec 17Dec 23Dec 28Jan 1Jan 6Jan 15Jan 30
20°FDec 18Dec 25Dec 31Jan 2Jan 6Jan 14Jan 24Feb 1Feb 5
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°F257249242236231226220214206
32°F296285277271264257250243235
28°F342331321312305297289281269
24°F365365362354347340331322309
20°F365365365365365365365358343
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
75% of years
20°F or colder
24% of years
16°F or colder
5% 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
1,963
Cooling degree days, base 65°F
2,236
Growing degree days, base 40°F
9,425
Growing degree days, base 45°F
7,673
Growing degree days, base 50°F
6,036
Growing degree days, base 55°F
4,572
Growing degree days, base 60°F
3,306

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January477077
February3622114
March24113259
April9666423
May18234681
June0479928
July0502967
August0446911
September1340789
October46136556
November23718253
December485077

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 0.1 km from Tombstone. 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 USC00028619 (Tombstone). Public domain.