Harrisburg climate

Harrisburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Poinsett SP, 4.4 km from Harrisburg, elevation 345 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Poinsett SP. 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 28 and the first fall freeze around November 7, a growing season of about 224 days.

Median at 36°F
last April 8, first October 29
Median at 32°F
last March 28, first November 7
Median at 28°F
last March 15, first November 19

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 25Apr 18Apr 14Apr 11Apr 8Apr 5Apr 2Mar 30Mar 23
32°FApr 11Apr 6Apr 3Mar 31Mar 28Mar 25Mar 21Mar 16Mar 8
28°FApr 2Mar 27Mar 22Mar 18Mar 15Mar 11Mar 7Mar 3Feb 26
24°FMar 22Mar 16Mar 10Mar 6Mar 3Feb 28Feb 25Feb 19Feb 9
20°FMar 11Mar 5Feb 28Feb 24Feb 19Feb 13Feb 7Feb 2Jan 27
16°FMar 2Feb 22Feb 13Feb 6Feb 1Jan 29Jan 24Jan 16Jan 8

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 15Oct 20Oct 24Oct 26Oct 29Oct 31Nov 2Nov 5Nov 10
32°FOct 26Oct 30Nov 1Nov 5Nov 7Nov 10Nov 14Nov 17Nov 23
28°FNov 4Nov 8Nov 12Nov 16Nov 19Nov 22Nov 26Dec 1Dec 7
24°FNov 13Nov 19Nov 23Nov 28Dec 1Dec 5Dec 10Dec 16Dec 24
20°FNov 25Dec 2Dec 8Dec 14Dec 21Dec 25Dec 31Jan 5Jan 13
16°FDec 9Dec 19Dec 25Dec 30Jan 2Jan 7Jan 13Jan 19Jan 29

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°F223216211207202199194189181
32°F248239233228224220216210202
28°F273264258253248243239233225
24°F303291284278272267261254246
20°F334323315307301296289281270
16°F363351342335330324315307298

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
93% 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
3,640
Cooling degree days, base 65°F
1,721
Growing degree days, base 40°F
7,631
Growing degree days, base 45°F
6,157
Growing degree days, base 50°F
4,830
Growing degree days, base 55°F
3,645
Growing degree days, base 60°F
2,608

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January856118
February646138
March4757121
April19842315
May48156574
June1339787
July0448913
August0425890
September16238672
October17660362
November4645108
December760131

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 4.4 km from Harrisburg. 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 USC00035831 (Poinsett SP). Public domain.