Delaware County climate

Delaware County Frost Dates and Growing Season

NOAA 1991-2020 normals for Marcus Hook, 10.5 km from Delaware County, elevation 10 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Marcus Hook. 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 30 and the first fall freeze around November 16, a growing season of about 230 days.

Median at 36°F
last April 9, first November 2
Median at 32°F
last March 30, first November 16
Median at 28°F
last March 20, first November 28

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 22Apr 17Apr 14Apr 11Apr 9Apr 6Apr 4Apr 2Mar 30
32°FApr 9Apr 5Apr 3Apr 1Mar 30Mar 27Mar 25Mar 21Mar 16
28°FMar 31Mar 28Mar 25Mar 22Mar 20Mar 17Mar 14Mar 10Mar 4
24°FMar 25Mar 20Mar 16Mar 14Mar 11Mar 8Mar 4Feb 28Feb 22
20°FMar 16Mar 11Mar 7Mar 4Mar 1Feb 26Feb 21Feb 14Feb 6
16°FMar 8Mar 2Feb 27Feb 22Feb 16Feb 10Feb 5Jan 31Jan 21

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 21Oct 26Oct 29Nov 1Nov 2Nov 5Nov 8Nov 12Nov 17
32°FNov 2Nov 6Nov 10Nov 13Nov 16Nov 19Nov 23Nov 27Dec 2
28°FNov 11Nov 16Nov 19Nov 23Nov 28Dec 1Dec 5Dec 9Dec 15
24°FNov 20Nov 29Dec 3Dec 6Dec 11Dec 15Dec 19Dec 24Jan 1
20°FDec 6Dec 13Dec 19Dec 24Dec 28Jan 1Jan 4Jan 9Jan 17
16°FDec 22Dec 28Jan 1Jan 5Jan 9Jan 13Jan 18Jan 24Feb 3

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°F224219214210206202198193187
32°F253245239234230226223218212
28°F275268262257252248243238231
24°F301293286280276271267261251
20°F323313306302298293289283274
16°F352336329323317312306302295

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
96% 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
4,289
Cooling degree days, base 65°F
1,457
Growing degree days, base 40°F
6,797
Growing degree days, base 45°F
5,413
Growing degree days, base 50°F
4,198
Growing degree days, base 55°F
3,134
Growing degree days, base 60°F
2,222

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January93404
February78803
March653137
April30616195
May9494465
June9284724
July0448913
August0395860
September23193620
October21226289
November491076
December778011

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 10.5 km from Delaware County. 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 USC00365390 (Marcus Hook). Public domain.