Collbran climate

Collbran Frost Dates and Growing Season

NOAA 1991-2020 normals for Collbran 1WSW, 1.7 km from Collbran, elevation 6009 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Collbran 1WSW. 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 17 and the first fall freeze around September 30, a growing season of about 136 days.

Median at 36°F
last May 31, first September 22
Median at 32°F
last May 17, first September 30
Median at 28°F
last May 3, first October 9

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 13Jun 8Jun 5Jun 2May 31May 28May 24May 22May 17
32°FJun 3May 29May 24May 21May 17May 14May 10May 6May 2
28°FMay 20May 15May 10May 6May 3May 1Apr 28Apr 24Apr 19
24°FMay 8May 3Apr 30Apr 26Apr 23Apr 19Apr 16Apr 12Apr 6
20°FApr 27Apr 22Apr 17Apr 13Apr 9Apr 6Apr 2Mar 28Mar 19
16°FApr 15Apr 7Apr 2Mar 27Mar 21Mar 16Mar 11Mar 7Mar 2

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 10Sep 14Sep 17Sep 19Sep 22Sep 24Sep 26Sep 29Oct 2
32°FSep 18Sep 22Sep 25Sep 28Sep 30Oct 2Oct 5Oct 8Oct 12
28°FSep 27Oct 1Oct 3Oct 6Oct 9Oct 11Oct 14Oct 17Oct 21
24°FOct 4Oct 8Oct 13Oct 16Oct 18Oct 21Oct 24Oct 28Nov 2
20°FOct 14Oct 19Oct 23Oct 26Oct 29Nov 1Nov 4Nov 7Nov 12
16°FOct 23Oct 30Nov 2Nov 5Nov 8Nov 11Nov 15Nov 18Nov 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°F13112512111711311010610196
32°F155148143139136131127122114
28°F177170166163159155150145138
24°F200192187182178174170165158
20°F227219213208203198194188180
16°F255246240235230224218211201

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
6,786
Cooling degree days, base 65°F
481
Growing degree days, base 40°F
4,437
Growing degree days, base 45°F
3,352
Growing degree days, base 50°F
2,423
Growing degree days, base 55°F
1,641
Growing degree days, base 60°F
991

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,27400
February98400
March786011
April561045
May3138201
June7581458
July4204665
August12154608
September13934356
October508076
November86704
December1,26300

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 1.7 km from Collbran. 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 USC00051743 (Collbran 1WSW). Public domain.