Dennehotso climate

Dennehotso Frost Dates and Growing Season

NOAA 1991-2020 normals for Mexican Hat, 33.8 km from Dennehotso, elevation 4109 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mexican Hat. 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 April 11 and the first fall freeze around October 30, a growing season of about 201 days.

Median at 36°F
last April 23, first October 20
Median at 32°F
last April 11, first October 30
Median at 28°F
last March 30, first November 8

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 4Apr 30Apr 28Apr 25Apr 23Apr 20Apr 17Apr 14Apr 9
32°FApr 26Apr 20Apr 17Apr 13Apr 11Apr 8Apr 5Apr 2Mar 27
28°FApr 16Apr 9Apr 5Apr 2Mar 30Mar 25Mar 19Mar 14Mar 9
24°FApr 6Mar 29Mar 19Mar 13Mar 9Mar 5Mar 1Feb 25Feb 15
20°FMar 18Mar 7Mar 1Feb 26Feb 20Feb 14Feb 8Feb 2Jan 26
16°FFeb 28Feb 19Feb 12Feb 6Feb 1Jan 28Jan 20Jan 11Jan 1

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 6Oct 11Oct 14Oct 18Oct 20Oct 22Oct 25Oct 28Nov 1
32°FOct 17Oct 22Oct 25Oct 28Oct 30Nov 1Nov 4Nov 7Nov 11
28°FOct 27Nov 1Nov 3Nov 6Nov 8Nov 11Nov 14Nov 17Nov 21
24°FNov 5Nov 10Nov 13Nov 16Nov 18Nov 21Nov 23Nov 26Dec 1
20°FNov 15Nov 20Nov 23Nov 26Nov 28Dec 1Dec 4Dec 8Dec 14
16°FNov 25Nov 30Dec 3Dec 7Dec 11Dec 15Dec 20Dec 26Jan 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°F198192187184180176173167161
32°F220214209205201197193188182
28°F248241234229225221215210203
24°F281272265259254249244235223
20°F313301295289284278272265254
16°F344334327320314307301294283

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
99% 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
4,304
Cooling degree days, base 65°F
1,840
Growing degree days, base 40°F
7,159
Growing degree days, base 45°F
5,798
Growing degree days, base 50°F
4,596
Growing degree days, base 55°F
3,541
Growing degree days, base 60°F
2,626

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January94200
February69704
March506062
April2719211
May70115511
June4370816
July05891,054
August0505970
September17233666
October22420276
November620025
December95300

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 33.8 km from Dennehotso. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00425582 (Mexican Hat). Public domain.