Grand County climate

Grand County Frost Dates and Growing Season

NOAA 1991-2020 normals for Williams Fork Dam, 10.3 km from Grand County, elevation 7618 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Williams Fork Dam. 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 12 and the first fall freeze around September 10, a growing season of about 89 days.

Median at 36°F
last June 28, first August 29
Median at 32°F
last June 12, first September 10
Median at 28°F
last May 26, first September 20

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°FJul 14Jul 7Jul 3Jun 30Jun 28Jun 25Jun 22Jun 20Jun 16
32°FJun 25Jun 22Jun 18Jun 15Jun 12Jun 9Jun 7Jun 4May 31
28°FJun 9Jun 5Jun 1May 30May 26May 23May 21May 17May 13
24°FMay 22May 18May 15May 11May 9May 7May 4May 2Apr 28
20°FMay 12May 6May 2Apr 30Apr 27Apr 24Apr 20Apr 16Apr 11
16°FMay 1Apr 25Apr 20Apr 16Apr 13Apr 10Apr 7Apr 4Mar 31

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°FAug 13Aug 19Aug 23Aug 25Aug 29Aug 31Sep 2Sep 5Sep 9
32°FAug 31Sep 3Sep 6Sep 8Sep 10Sep 12Sep 14Sep 17Sep 21
28°FSep 8Sep 12Sep 15Sep 18Sep 20Sep 23Sep 25Sep 28Oct 3
24°FSep 19Sep 23Sep 26Sep 29Oct 1Oct 4Oct 6Oct 10Oct 16
20°FSep 29Oct 3Oct 6Oct 10Oct 12Oct 15Oct 18Oct 21Oct 27
16°FOct 8Oct 13Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 6

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°F787167635955514537
32°F1059996928986827871
28°F13412712311911511210810497
24°F160154151147144141137133127
20°F185179174171167163158153147
16°F209203198194189184179175168

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
9,756
Cooling degree days, base 65°F
18
Growing degree days, base 40°F
2,577
Growing degree days, base 45°F
1,731
Growing degree days, base 50°F
1,036
Growing degree days, base 55°F
504
Growing degree days, base 60°F
157

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,61200
February1,33300
March1,13300
April81302
May561040
June2791189
July11012368
August1595313
September3750117
October74408
November1,11500
December1,52400

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 10.3 km from Grand County. 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 USC00059096 (Williams Fork Dam). Public domain.