Laramie County climate

Laramie County Frost Dates and Growing Season

NOAA 1991-2020 normals for Archer, 17.5 km from Laramie County, elevation 6010 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Archer. 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 21 and the first fall freeze around September 24, a growing season of about 124 days.

Median at 36°F
last June 3, first September 15
Median at 32°F
last May 21, first September 24
Median at 28°F
last May 9, first October 1

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 19Jun 14Jun 10Jun 6Jun 3Jun 1May 29May 25May 20
32°FJun 6Jun 1May 28May 24May 21May 19May 16May 12May 8
28°FMay 24May 18May 15May 11May 9May 6May 4May 1Apr 28
24°FMay 12May 7May 4May 2Apr 30Apr 27Apr 23Apr 20Apr 16
20°FMay 5Apr 30Apr 26Apr 23Apr 19Apr 16Apr 12Apr 9Apr 4
16°FApr 26Apr 19Apr 15Apr 11Apr 7Apr 3Mar 31Mar 26Mar 20

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 6Sep 9Sep 12Sep 15Sep 17Sep 20Sep 22Sep 26
32°FSep 8Sep 14Sep 18Sep 22Sep 24Sep 26Sep 29Oct 1Oct 5
28°FSep 18Sep 24Sep 27Sep 29Oct 1Oct 4Oct 8Oct 11Oct 16
24°FSep 27Oct 1Oct 4Oct 8Oct 11Oct 14Oct 17Oct 21Oct 26
20°FOct 5Oct 10Oct 14Oct 17Oct 21Oct 24Oct 27Oct 30Nov 4
16°FOct 13Oct 19Oct 23Oct 26Oct 29Nov 1Nov 5Nov 9Nov 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°F12111411010610298938981
32°F141136131128124120115111103
28°F162157152148144140136131123
24°F182176171167163159154149142
20°F204196191186182178174168161
16°F226218212207202197192186178

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
7,023
Cooling degree days, base 65°F
389
Growing degree days, base 40°F
4,072
Growing degree days, base 45°F
3,021
Growing degree days, base 50°F
2,137
Growing degree days, base 55°F
1,410
Growing degree days, base 60°F
824

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,13600
February99600
March86808
April657036
May3945152
June12957384
July24178620
August37117546
September19430307
October570174
November874011
December1,14400

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 17.5 km from Laramie 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 USC00480270 (Archer). Public domain.