Basalt climate

Basalt Frost Dates and Growing Season

NOAA 1991-2020 normals for Aspen Pitkin CO AP, 21.5 km from Basalt, elevation 7721 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Aspen Pitkin CO 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 31 and the first fall freeze around September 23, a growing season of about 114 days.

Median at 36°F
last June 12, first September 13
Median at 32°F
last May 31, first September 23
Median at 28°F
last May 13, first October 2

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 26Jun 21Jun 18Jun 15Jun 12Jun 10Jun 8Jun 4May 31
32°FJun 14Jun 9Jun 5Jun 2May 31May 28May 24May 20May 16
28°FJun 1May 24May 20May 17May 13May 9May 6May 3Apr 29
24°FMay 14May 9May 5May 2Apr 30Apr 26Apr 23Apr 20Apr 15
20°FMay 3Apr 27Apr 23Apr 20Apr 16Apr 13Apr 10Apr 6Apr 2
16°FApr 20Apr 14Apr 10Apr 6Apr 3Apr 1Mar 28Mar 24Mar 17

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 1Sep 5Sep 8Sep 11Sep 13Sep 15Sep 17Sep 20Sep 24
32°FSep 11Sep 15Sep 18Sep 20Sep 23Sep 25Sep 27Sep 30Oct 3
28°FSep 21Sep 25Sep 27Sep 30Oct 2Oct 4Oct 7Oct 10Oct 14
24°FSep 29Oct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 20Oct 24
20°FOct 7Oct 12Oct 15Oct 18Oct 21Oct 23Oct 26Oct 29Nov 3
16°FOct 17Oct 21Oct 24Oct 27Oct 29Nov 1Nov 4Nov 7Nov 13

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°F10710197949087837974
32°F13312612111711411010610094
28°F159153148144140136132126119
24°F182176171166163158155151144
20°F207200194190186182176171166
16°F230223217212209205200194187

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
8,142
Cooling degree days, base 65°F
90
Growing degree days, base 40°F
3,247
Growing degree days, base 45°F
2,298
Growing degree days, base 50°F
1,507
Growing degree days, base 55°F
866
Growing degree days, base 60°F
380

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,34400
February1,11400
March97700
April71007
May464087
June17513295
July4047473
August7726414
September2692205
October640026
November99200
December1,34100

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 21.5 km from Basalt. 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 USW00093073 (Aspen Pitkin CO AP). Public domain.