Larimer County climate

Larimer County Frost Dates and Growing Season

NOAA 1991-2020 normals for Buckhorn Mtn 1 E, 14.9 km from Larimer County, elevation 7400 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Buckhorn Mtn 1 E. 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 29, a growing season of about 128 days.

Median at 36°F
last June 1, first September 21
Median at 32°F
last May 21, first September 29
Median at 28°F
last May 11, first October 6

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 15Jun 9Jun 6Jun 3Jun 1May 29May 26May 23May 18
32°FJun 4May 31May 27May 24May 21May 18May 16May 13May 9
28°FMay 26May 21May 17May 14May 11May 8May 6May 2Apr 29
24°FMay 16May 11May 7May 4May 1Apr 29Apr 25Apr 21Apr 17
20°FMay 6May 1Apr 28Apr 24Apr 20Apr 17Apr 14Apr 9Apr 1
16°FApr 28Apr 22Apr 17Apr 13Apr 9Apr 4Mar 31Mar 25Mar 14

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 6Sep 11Sep 15Sep 18Sep 21Sep 23Sep 26Sep 29Oct 3
32°FSep 12Sep 19Sep 23Sep 26Sep 29Oct 1Oct 3Oct 7Oct 12
28°FSep 22Sep 28Oct 1Oct 3Oct 6Oct 10Oct 13Oct 17Oct 22
24°FOct 1Oct 4Oct 8Oct 11Oct 15Oct 19Oct 22Oct 28Nov 2
20°FOct 7Oct 13Oct 18Oct 22Oct 26Oct 31Nov 3Nov 8Nov 14
16°FOct 16Oct 22Oct 27Nov 1Nov 5Nov 9Nov 13Nov 19Nov 25

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°F1261211171131101061009589
32°F148140136132128124120115107
28°F167160155150146142137131124
24°F189182175170166161157152143
20°F214205198192188183177171162
16°F240229223216211204197191182

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
7,154
Cooling degree days, base 65°F
300
Growing degree days, base 40°F
3,797
Growing degree days, base 45°F
2,762
Growing degree days, base 50°F
1,910
Growing degree days, base 55°F
1,219
Growing degree days, base 60°F
681

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,07001
February98101
March89108
April736021
May4862107
June17341331
July43128551
August6396499
September22533291
October578183
November830017
December1,07901

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 14.9 km from Larimer County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00051060 (Buckhorn Mtn 1 E). Public domain.