Circle climate

Circle Frost Dates and Growing Season

NOAA 1991-2020 normals for Circle, 0.6 km from Circle, elevation 2480 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Circle. 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 22, a growing season of about 126 days.

Median at 36°F
last May 28, first September 13
Median at 32°F
last May 17, first September 22
Median at 28°F
last May 6, 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 15Jun 6Jun 3May 31May 28May 25May 23May 19May 15
32°FMay 31May 26May 23May 20May 17May 15May 12May 8May 4
28°FMay 21May 16May 12May 9May 6May 4May 1Apr 28Apr 22
24°FMay 9May 4May 1Apr 28Apr 26Apr 22Apr 19Apr 15Apr 8
20°FApr 30Apr 25Apr 20Apr 17Apr 14Apr 10Apr 6Apr 2Mar 28
16°FApr 20Apr 14Apr 10Apr 6Apr 3Mar 31Mar 28Mar 21Mar 15

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 30Sep 3Sep 7Sep 10Sep 13Sep 16Sep 19Sep 22Sep 26
32°FSep 7Sep 13Sep 17Sep 20Sep 22Sep 25Sep 28Oct 1Oct 6
28°FSep 17Sep 22Sep 25Sep 28Oct 1Oct 4Oct 7Oct 11Oct 17
24°FSep 24Sep 29Oct 3Oct 7Oct 11Oct 15Oct 18Oct 22Oct 26
20°FOct 2Oct 9Oct 14Oct 18Oct 21Oct 24Oct 26Oct 30Nov 3
16°FOct 14Oct 19Oct 23Oct 27Oct 30Nov 1Nov 5Nov 8Nov 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°F126119114110106103989285
32°F145139135131126122118112105
28°F167159154150146142138133126
24°F189182176172168163157152145
20°F209202197192188183179172163
16°F231222215210206202197192184

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
7,832
Cooling degree days, base 65°F
601
Growing degree days, base 40°F
4,349
Growing degree days, base 45°F
3,327
Growing degree days, base 50°F
2,441
Growing degree days, base 55°F
1,690
Growing degree days, base 60°F
1,073

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,45200
February1,20301
March97508
April604150
May32313203
June9776431
July17237685
August29218655
September19354329
October594375
November99006
December1,35600

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 0.6 km from Circle. 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 USC00241758 (Circle). Public domain.