Castle Pines climate

Castle Pines Frost Dates and Growing Season

NOAA 1991-2020 normals for Castle Rock, 5.3 km from Castle Pines, elevation 6185 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Castle Rock. 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 9 and the first fall freeze around October 2, a growing season of about 143 days.

Median at 36°F
last May 21, first September 25
Median at 32°F
last May 9, first October 2
Median at 28°F
last May 1, first October 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°FJun 6May 31May 28May 24May 21May 18May 15May 12May 9
32°FMay 24May 18May 15May 12May 9May 7May 5May 3Apr 30
28°FMay 14May 10May 6May 4May 1Apr 29Apr 25Apr 21Apr 17
24°FMay 8May 2Apr 28Apr 24Apr 21Apr 17Apr 14Apr 9Apr 4
20°FApr 27Apr 21Apr 17Apr 13Apr 9Apr 5Apr 2Mar 30Mar 22
16°FApr 18Apr 12Apr 7Apr 3Apr 1Mar 27Mar 22Mar 15Mar 7

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 11Sep 16Sep 20Sep 23Sep 25Sep 27Sep 30Oct 2Oct 7
32°FSep 17Sep 23Sep 27Sep 30Oct 2Oct 5Oct 8Oct 12Oct 16
28°FSep 26Oct 2Oct 5Oct 9Oct 12Oct 14Oct 17Oct 21Oct 25
24°FOct 6Oct 12Oct 15Oct 18Oct 21Oct 24Oct 27Oct 30Nov 4
20°FOct 15Oct 20Oct 24Oct 27Oct 30Nov 2Nov 5Nov 9Nov 14
16°FOct 21Oct 26Nov 1Nov 3Nov 6Nov 10Nov 14Nov 17Nov 22

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°F142136131127124120115110103
32°F161155151147143140135130124
28°F181175170165161157153148141
24°F202194189185181176171166157
20°F221213207203198194189184176
16°F244235228222217213207201192

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
6,103
Cooling degree days, base 65°F
499
Growing degree days, base 40°F
4,661
Growing degree days, base 45°F
3,483
Growing degree days, base 50°F
2,491
Growing degree days, base 55°F
1,669
Growing degree days, base 60°F
1,005

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02901
February88803
March771019
April577156
May32111207
June7989462
July11198652
August21149594
September14847363
October4772110
November756023
December1,02802

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 5.3 km from Castle Pines. 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 USC00051401 (Castle Rock). Public domain.