Alta climate

Alta Frost Dates and Growing Season

NOAA 1991-2020 normals for Blue Canyon AP, 11.7 km from Alta, elevation 5276 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Blue Canyon AP. 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 4 and the first fall freeze around November 4, a growing season of about 183 days.

Median at 36°F
last May 22, first October 20
Median at 32°F
last May 4, first November 4
Median at 28°F
last April 16, first November 23

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 10Jun 3May 31May 27May 22May 16May 11May 6Apr 27
32°FMay 31May 24May 15May 9May 4Apr 29Apr 25Apr 19Apr 12
28°FMay 13May 3Apr 28Apr 23Apr 16Apr 12Apr 6Mar 31Mar 17
24°FApr 25Apr 15Apr 8Apr 4Mar 29Mar 20Mar 9Feb 28Feb 10
20°FApr 6Mar 24Mar 10Feb 28Feb 20Feb 10Jan 27Jan 12Dec 31
16°FFeb 27Feb 15Feb 4Jan 25Jan 14Jan 8Jan 3Dec 30Dec 18

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 28Oct 5Oct 11Oct 16Oct 20Oct 24Oct 30Nov 4Nov 10
32°FOct 12Oct 20Oct 26Nov 1Nov 4Nov 8Nov 13Nov 18Nov 26
28°FNov 1Nov 7Nov 13Nov 17Nov 23Nov 28Dec 2Dec 7Dec 15
24°FNov 14Nov 23Dec 1Dec 5Dec 10Dec 16Dec 23Jan 1Jan 15
20°FNov 28Dec 7Dec 15Dec 23Dec 31Jan 4Jan 13Jan 25Feb 17
16°FDec 11Dec 19Dec 29Jan 1Jan 5Jan 12Jan 20Feb 2Feb 16

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°F183172165158153147140133123
32°F219206197188183175168160150
28°F255244235227219213204195183
24°F310292279269259251244234219
20°F365355336324313303289275259
16°F365365365365365365354336308

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
87% 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
5,213
Cooling degree days, base 65°F
552
Growing degree days, base 40°F
5,021
Growing degree days, base 45°F
3,748
Growing degree days, base 50°F
2,671
Growing degree days, base 55°F
1,789
Growing degree days, base 60°F
1,088

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January761019
February727013
March730026
April608056
May38415183
June14861377
July20183627
August22170613
September102103459
October31521229
November598158
December800012

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 11.7 km from Alta. 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 USW00023225 (Blue Canyon AP). Public domain.