Downingtown climate

Downingtown Frost Dates and Growing Season

NOAA 1991-2020 normals for W Chester 2 Nw, 7.1 km from Downingtown, elevation 375 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for W Chester 2 Nw. 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 26 and the first fall freeze around October 18, a growing season of about 174 days.

Median at 36°F
last May 7, first October 7
Median at 32°F
last April 26, first October 18
Median at 28°F
last April 11, first October 30

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 22May 18May 13May 10May 7May 4May 1Apr 28Apr 23
32°FMay 11May 6May 2Apr 29Apr 26Apr 23Apr 20Apr 16Apr 10
28°FApr 26Apr 22Apr 18Apr 15Apr 11Apr 8Apr 5Apr 1Mar 28
24°FApr 15Apr 8Apr 5Apr 2Mar 31Mar 28Mar 25Mar 20Mar 15
20°FApr 3Mar 30Mar 26Mar 22Mar 18Mar 15Mar 12Mar 8Mar 1
16°FMar 22Mar 17Mar 13Mar 10Mar 7Mar 3Feb 28Feb 25Feb 18

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 27Oct 1Oct 3Oct 5Oct 7Oct 9Oct 12Oct 17Oct 22
32°FOct 4Oct 9Oct 12Oct 15Oct 18Oct 21Oct 24Oct 28Nov 1
28°FOct 14Oct 19Oct 24Oct 27Oct 30Nov 1Nov 3Nov 6Nov 11
24°FOct 29Nov 1Nov 4Nov 6Nov 8Nov 11Nov 14Nov 18Nov 24
20°FNov 7Nov 11Nov 14Nov 19Nov 22Nov 24Nov 29Dec 3Dec 9
16°FNov 17Nov 23Nov 28Dec 2Dec 6Dec 9Dec 14Dec 20Dec 28

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°F171164160156152148144140134
32°F194186182177174169165160152
28°F218212206202198194190185178
24°F245238231226223219215211203
20°F272263258253248244239233226
16°F300292285279273269263258250

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
5,478
Cooling degree days, base 65°F
918
Growing degree days, base 40°F
5,568
Growing degree days, base 45°F
4,342
Growing degree days, base 50°F
3,270
Growing degree days, base 55°F
2,348
Growing degree days, base 60°F
1,563

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09701
February92803
March781021
April4409119
May18252343
June26186611
July1310773
August5252713
September7298477
October35911169
November650033
December93608

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 7.1 km from Downingtown. 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 USC00369464 (W Chester 2 Nw). Public domain.