Skippack climate

Skippack Frost Dates and Growing Season

NOAA 1991-2020 normals for Graterford 1 E, 2.3 km from Skippack, elevation 279 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Graterford 1 E. 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 24 and the first fall freeze around October 15, a growing season of about 173 days.

Median at 36°F
last May 4, first October 4
Median at 32°F
last April 24, first October 15
Median at 28°F
last April 10, first October 27

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 21May 15May 11May 8May 4May 2Apr 30Apr 26Apr 21
32°FMay 9May 4May 1Apr 28Apr 24Apr 21Apr 18Apr 15Apr 10
28°FApr 27Apr 20Apr 17Apr 13Apr 10Apr 7Apr 4Apr 1Mar 28
24°FApr 14Apr 8Apr 5Apr 2Mar 30Mar 27Mar 24Mar 20Mar 14
20°FApr 3Mar 29Mar 25Mar 22Mar 18Mar 15Mar 10Mar 7Mar 2
16°FMar 21Mar 16Mar 12Mar 8Mar 5Mar 2Feb 28Feb 23Feb 16

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 21Sep 26Sep 30Oct 2Oct 4Oct 6Oct 9Oct 13Oct 18
32°FOct 1Oct 5Oct 8Oct 11Oct 15Oct 18Oct 22Oct 26Nov 1
28°FOct 10Oct 16Oct 20Oct 24Oct 27Nov 1Nov 3Nov 7Nov 12
24°FOct 23Oct 30Nov 3Nov 6Nov 10Nov 13Nov 17Nov 21Nov 27
20°FNov 7Nov 12Nov 16Nov 20Nov 24Nov 28Dec 1Dec 5Dec 12
16°FNov 18Nov 24Nov 29Dec 2Dec 6Dec 11Dec 16Dec 22Dec 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°F170164160155151146141137131
32°F193186181177173169164159151
28°F221214208204198193189183174
24°F249240234229226221215210200
20°F276267261256252247242236226
16°F303295287281276271266260252

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
5,475
Cooling degree days, base 65°F
906
Growing degree days, base 40°F
5,527
Growing degree days, base 45°F
4,301
Growing degree days, base 50°F
3,234
Growing degree days, base 55°F
2,311
Growing degree days, base 60°F
1,537

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,08502
February92103
March791020
April4437111
May18249339
June29183605
July2310773
August7248707
September8696463
October36213169
November639036
December93008

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 2.3 km from Skippack. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00363437 (Graterford 1 E). Public domain.