Shelby climate

Shelby Frost Dates and Growing Season

NOAA 1991-2020 normals for Harlan, 17.3 km from Shelby, elevation 1270 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Harlan. 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 April 27 and the first fall freeze around October 9, a growing season of about 165 days.

Median at 36°F
last May 5, first September 30
Median at 32°F
last April 27, first October 9
Median at 28°F
last April 17, first October 20

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°FMay 18May 13May 10May 7May 5May 2Apr 30Apr 27Apr 23
32°FMay 9May 5May 2Apr 30Apr 27Apr 24Apr 21Apr 17Apr 12
28°FApr 30Apr 26Apr 22Apr 19Apr 17Apr 14Apr 11Apr 7Apr 3
24°FApr 22Apr 17Apr 13Apr 10Apr 7Apr 5Apr 2Mar 31Mar 24
20°FApr 14Apr 9Apr 5Apr 3Mar 31Mar 29Mar 24Mar 20Mar 14
16°FApr 5Mar 31Mar 28Mar 25Mar 21Mar 18Mar 14Mar 10Mar 5

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 15Sep 21Sep 24Sep 27Sep 30Oct 3Oct 5Oct 9Oct 14
32°FSep 24Sep 29Oct 3Oct 6Oct 9Oct 12Oct 15Oct 18Oct 22
28°FOct 4Oct 10Oct 14Oct 17Oct 20Oct 22Oct 24Oct 28Nov 1
24°FOct 16Oct 21Oct 24Oct 26Oct 29Nov 1Nov 3Nov 6Nov 11
20°FOct 23Oct 28Nov 1Nov 3Nov 5Nov 8Nov 11Nov 15Nov 21
16°FNov 1Nov 4Nov 8Nov 11Nov 14Nov 17Nov 20Nov 26Dec 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°F165158153150147144140135128
32°F183177173169165161157151145
28°F204197192188184181176172165
24°F221215210206203200196192184
20°F243235230225220216212207201
16°F262253248243239234229223216

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
6,566
Cooling degree days, base 65°F
957
Growing degree days, base 40°F
5,418
Growing degree days, base 45°F
4,293
Growing degree days, base 50°F
3,280
Growing degree days, base 55°F
2,382
Growing degree days, base 60°F
1,604

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,37900
February1,12801
March851130
April4628119
May17168374
June18220652
July3306767
August10239694
September98100456
October41015167
November822019
December1,21501

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 17.3 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 USC00133632 (Harlan). Public domain.