Gettysburg climate

Gettysburg Frost Dates and Growing Season

NOAA 1991-2020 normals for Gettysburg, 1.5 km from Gettysburg, elevation 2084 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Gettysburg. 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 7 and the first fall freeze around October 2, a growing season of about 147 days.

Median at 36°F
last May 17, first September 24
Median at 32°F
last May 7, first October 2
Median at 28°F
last April 29, first October 10

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 29May 25May 22May 19May 17May 14May 11May 9May 4
32°FMay 21May 16May 13May 10May 7May 5May 2Apr 30Apr 24
28°FMay 11May 7May 4May 1Apr 29Apr 25Apr 21Apr 17Apr 12
24°FMay 2Apr 29Apr 24Apr 20Apr 17Apr 13Apr 10Apr 7Apr 3
20°FApr 24Apr 18Apr 13Apr 10Apr 8Apr 5Apr 3Mar 31Mar 24
16°FApr 15Apr 9Apr 6Apr 3Apr 1Mar 29Mar 24Mar 19Mar 14

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 12Sep 16Sep 20Sep 22Sep 24Sep 26Sep 28Oct 1Oct 5
32°FSep 21Sep 25Sep 28Sep 30Oct 2Oct 4Oct 7Oct 11Oct 16
28°FSep 28Oct 1Oct 4Oct 7Oct 10Oct 14Oct 17Oct 20Oct 24
24°FOct 4Oct 9Oct 13Oct 17Oct 20Oct 23Oct 25Oct 28Nov 1
20°FOct 14Oct 20Oct 24Oct 27Oct 30Nov 1Nov 4Nov 7Nov 12
16°FOct 23Oct 28Nov 1Nov 4Nov 6Nov 9Nov 12Nov 15Nov 20

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°F147141137134130127123119114
32°F165159155151147144140135130
28°F185178174170165161157152145
24°F205198193188184181176171163
20°F224216210206203199194189182
16°F241234228223219215210205199

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
8,117
Cooling degree days, base 65°F
615
Growing degree days, base 40°F
4,393
Growing degree days, base 45°F
3,396
Growing degree days, base 50°F
2,518
Growing degree days, base 55°F
1,757
Growing degree days, base 60°F
1,121

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,54800
February1,28201
March1,05707
April635249
May31021224
June69104486
July14232683
August26194632
September17959348
October582483
November1,00405
December1,41000

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 1.5 km from Gettysburg. 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 USC00393294 (Gettysburg). Public domain.