Granby climate

Granby Frost Dates and Growing Season

NOAA 1991-2020 normals for Grand Lake 6 Ssw, 12.6 km from Granby, elevation 8288 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Grand Lake 6 Ssw. 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 June 13 and the first fall freeze around September 7, a growing season of about 84 days.

Median at 32°F
last June 13, first September 7
Median at 28°F
last May 26, first September 22

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°F–––––––––
32°FJun 28Jun 23Jun 19Jun 17Jun 13Jun 10Jun 8Jun 5Jun 1
28°FJun 10Jun 5Jun 2May 30May 26May 23May 20May 17May 12
24°FMay 23May 18May 15May 12May 10May 7May 5May 2Apr 29
20°FMay 14May 9May 5May 2Apr 30Apr 27Apr 24Apr 21Apr 16
16°FMay 4May 1Apr 27Apr 23Apr 20Apr 15Apr 13Apr 10Apr 5

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°F–––––––––
32°FAug 21Aug 29Sep 2Sep 5Sep 7Sep 10Sep 13Sep 16Sep 21
28°FSep 8Sep 13Sep 16Sep 19Sep 22Sep 24Sep 27Oct 1Oct 4
24°FSep 22Sep 26Sep 30Oct 2Oct 5Oct 7Oct 10Oct 13Oct 18
20°FOct 3Oct 7Oct 10Oct 14Oct 17Oct 19Oct 21Oct 25Oct 30
16°FOct 11Oct 16Oct 19Oct 22Oct 26Oct 28Oct 31Nov 3Nov 7

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°F746861575347423731
32°F1039792898480757061
28°F13913112612211811411010597
24°F166159154150146143139135129
20°F187181177173169165161157150
16°F206200196192187183179173166

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
10,017
Cooling degree days, base 65°F
2
Growing degree days, base 40°F
2,244
Growing degree days, base 45°F
1,433
Growing degree days, base 50°F
778
Growing degree days, base 55°F
305
Growing degree days, base 60°F
54

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,57600
February1,33000
March1,19200
April87900
May608019
June3270139
July1731293
August2251242
September410081
October74703
November1,09100
December1,46000

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 12.6 km from Granby. 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 USC00053500 (Grand Lake 6 Ssw). Public domain.