Shelby climate

Shelby Frost Dates and Growing Season

NOAA 1991-2020 normals for Alabaster Shelby CO AP, 19.9 km from Shelby, elevation 565 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Alabaster Shelby CO AP. 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 March 12 and the first fall freeze around November 16, a growing season of about 248 days.

Median at 36°F
last March 27, first November 4
Median at 32°F
last March 12, first November 16
Median at 28°F
last February 27, first December 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°FApr 14Apr 8Apr 4Mar 31Mar 27Mar 23Mar 19Mar 14Mar 7
32°FMar 31Mar 25Mar 20Mar 16Mar 12Mar 8Mar 3Feb 26Feb 20
28°FMar 17Mar 11Mar 7Mar 2Feb 27Feb 22Feb 17Feb 10Jan 31
24°FMar 6Feb 27Feb 20Feb 13Feb 7Feb 2Jan 29Jan 20Jan 11
20°FFeb 22Feb 9Feb 2Jan 29Jan 24Jan 19Jan 13Jan 6Dec 31
16°FFeb 7Jan 31Jan 25Jan 20Jan 15Jan 11Jan 7Jan 3Dec 27

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°FOct 23Oct 28Oct 31Nov 2Nov 4Nov 7Nov 10Nov 15Nov 21
32°FNov 1Nov 5Nov 9Nov 12Nov 16Nov 19Nov 23Nov 28Dec 4
28°FNov 10Nov 16Nov 20Nov 25Dec 1Dec 3Dec 8Dec 18Dec 28
24°FNov 24Dec 1Dec 7Dec 14Dec 22Dec 27Jan 1Jan 7Jan 16
20°FDec 9Dec 20Dec 27Jan 1Jan 4Jan 8Jan 14Jan 19Jan 30
16°FDec 20Dec 29Jan 2Jan 5Jan 9Jan 14Jan 18Jan 23Feb 1

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°F248239232227221217212206199
32°F277267260254248244239233224
28°F311299290284278273267260250
24°F343334328320312305299290277
20°F365365359351342335330321307
16°F365365365365365365354342332

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
97% of years
20°F or colder
76% of years
16°F or colder
45% 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
2,378
Cooling degree days, base 65°F
2,182
Growing degree days, base 40°F
9,035
Growing degree days, base 45°F
7,369
Growing degree days, base 50°F
5,835
Growing degree days, base 55°F
4,446
Growing degree days, base 60°F
3,225

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January602273
February4285105
March27222252
April10474423
May17227674
June0405855
July0507972
August0493958
September4328774
October99102471
November32613184
December527495

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 19.9 km from Shelby. 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 USW00053864 (Alabaster Shelby CO AP). Public domain.