Shelby climate

Shelby Frost Dates and Growing Season

NOAA 1991-2020 normals for Shelby, 0.9 km from Shelby, elevation 3325 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Shelby. 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 23 and the first fall freeze around September 16, a growing season of about 115 days.

Median at 36°F
last June 5, first September 5
Median at 32°F
last May 23, first September 16
Median at 28°F
last May 10, first September 26

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 21Jun 16Jun 11Jun 8Jun 5Jun 3May 31May 28May 23
32°FJun 6Jun 1May 28May 26May 23May 20May 18May 14May 11
28°FMay 22May 18May 14May 12May 10May 7May 5May 2Apr 30
24°FMay 12May 7May 4May 2Apr 29Apr 26Apr 23Apr 19Apr 14
20°FMay 3Apr 30Apr 26Apr 21Apr 18Apr 14Apr 10Apr 7Apr 2
16°FApr 26Apr 19Apr 14Apr 11Apr 7Apr 4Apr 1Mar 29Mar 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°FAug 23Aug 28Aug 31Sep 3Sep 5Sep 7Sep 10Sep 14Sep 18
32°FSep 3Sep 7Sep 10Sep 13Sep 16Sep 19Sep 21Sep 24Sep 28
28°FSep 13Sep 17Sep 21Sep 24Sep 26Sep 28Oct 1Oct 3Oct 7
24°FSep 21Sep 27Sep 30Oct 3Oct 5Oct 7Oct 10Oct 14Oct 18
20°FOct 1Oct 5Oct 8Oct 12Oct 15Oct 18Oct 21Oct 24Oct 28
16°FOct 8Oct 13Oct 17Oct 21Oct 24Oct 26Oct 29Nov 1Nov 5

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°F10710197949086827770
32°F13212712211911511110710297
28°F155149145142138136132127121
24°F178171167163159156151145140
20°F200193187182178174170165157
16°F218211205201197192187181173

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
8,532
Cooling degree days, base 65°F
242
Growing degree days, base 40°F
3,424
Growing degree days, base 45°F
2,481
Growing degree days, base 50°F
1,697
Growing degree days, base 55°F
1,059
Growing degree days, base 60°F
569

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,43400
February1,18700
March1,04902
April711018
May4314122
June19019287
July52109522
August7497490
September29212213
October695041
November1,05603
December1,36100

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 0.9 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 USC00247500 (Shelby). Public domain.