Pottstown climate

Pottstown Frost Dates and Growing Season

NOAA 1991-2020 normals for Pottstown Limerick AP, 7.9 km from Pottstown, elevation 291 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Pottstown Limerick AP. 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 20 and the first fall freeze around October 23, a growing season of about 186 days.

Median at 36°F
last May 2, first October 12
Median at 32°F
last April 20, first October 23
Median at 28°F
last April 6, first November 3

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 19May 12May 9May 5May 2Apr 29Apr 25Apr 22Apr 18
32°FMay 6May 1Apr 27Apr 23Apr 20Apr 17Apr 14Apr 10Apr 5
28°FApr 21Apr 16Apr 12Apr 9Apr 6Apr 3Apr 1Mar 29Mar 23
24°FApr 8Apr 4Mar 31Mar 29Mar 26Mar 23Mar 19Mar 16Mar 10
20°FMar 29Mar 24Mar 21Mar 18Mar 15Mar 12Mar 8Mar 4Feb 27
16°FMar 19Mar 14Mar 10Mar 7Mar 3Feb 28Feb 24Feb 18Feb 10

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 1Oct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 21Oct 26
32°FOct 9Oct 13Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 5
28°FOct 19Oct 24Oct 29Nov 1Nov 3Nov 6Nov 9Nov 13Nov 18
24°FNov 1Nov 5Nov 9Nov 12Nov 15Nov 19Nov 22Nov 26Dec 3
20°FNov 10Nov 16Nov 21Nov 26Nov 30Dec 3Dec 7Dec 13Dec 20
16°FNov 24Dec 1Dec 5Dec 10Dec 15Dec 20Dec 25Dec 31Jan 7

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°F182175170166162158154148142
32°F207201195190186180177171164
28°F232225220216212207202198188
24°F258250245240235231226222214
20°F285276270265260255250244236
16°F310302296291287281276270260

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
5,534
Cooling degree days, base 65°F
794
Growing degree days, base 40°F
5,394
Growing degree days, base 45°F
4,175
Growing degree days, base 50°F
3,108
Growing degree days, base 55°F
2,187
Growing degree days, base 60°F
1,414

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09402
February92704
March783022
April4399116
May18443331
June32155573
July2281744
August7219677
September8778442
October3719160
November659031
December94906

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 7.9 km from Pottstown. 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 USW00054782 (Pottstown Limerick AP). Public domain.