Cortez climate

Cortez Frost Dates and Growing Season

NOAA 1991-2020 normals for Cortez, 0.9 km from Cortez, elevation 6167 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cortez. 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 May 12 and the first fall freeze around October 7, a growing season of about 147 days.

Median at 36°F
last May 26, first September 30
Median at 32°F
last May 12, first October 7
Median at 28°F
last April 30, first October 17

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°FJun 12Jun 6Jun 3May 31May 26May 23May 20May 17May 13
32°FMay 31May 23May 19May 15May 12May 9May 6May 3Apr 30
28°FMay 14May 8May 4May 2Apr 30Apr 27Apr 24Apr 20Apr 14
24°FMay 1Apr 26Apr 22Apr 18Apr 14Apr 11Apr 8Apr 4Mar 30
20°FApr 19Apr 11Apr 7Apr 2Mar 29Mar 24Mar 18Mar 12Mar 4
16°FMar 30Mar 21Mar 15Mar 11Mar 7Mar 3Feb 27Feb 22Feb 15

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°FSep 18Sep 22Sep 25Sep 27Sep 30Oct 2Oct 4Oct 7Oct 12
32°FSep 26Sep 30Oct 3Oct 5Oct 7Oct 10Oct 13Oct 16Oct 21
28°FOct 4Oct 8Oct 12Oct 15Oct 17Oct 21Oct 24Oct 27Nov 1
24°FOct 12Oct 17Oct 22Oct 25Oct 29Nov 1Nov 4Nov 7Nov 12
20°FOct 22Oct 29Nov 1Nov 5Nov 8Nov 11Nov 14Nov 17Nov 21
16°FNov 1Nov 8Nov 13Nov 16Nov 18Nov 20Nov 23Nov 26Nov 30

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°F143137132129125121117113105
32°F165160155151147144140134127
28°F191184180175171167163158152
24°F220211205201196192187182175
20°F252241235228224219214208199
16°F279271266261256250245237228

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
100% of years
16°F or colder
100% 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
5,817
Cooling degree days, base 65°F
682
Growing degree days, base 40°F
4,987
Growing degree days, base 45°F
3,811
Growing degree days, base 50°F
2,805
Growing degree days, base 55°F
1,954
Growing degree days, base 60°F
1,249

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09300
February85800
March719011
April504065
May25315251
June47118521
July2277739
August5214674
September9357417
October4211117
November75209
December1,07100

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 0.9 km from Cortez. 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 USC00051886 (Cortez). Public domain.