Donora climate

Donora Frost Dates and Growing Season

NOAA 1991-2020 normals for Donora 1 Sw, 1.4 km from Donora, elevation 762 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Donora 1 Sw. 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 27 and the first fall freeze around October 22, a growing season of about 177 days.

Median at 36°F
last May 6, first October 12
Median at 32°F
last April 27, first October 22
Median at 28°F
last April 14, first November 1

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 14May 10May 6May 3Apr 30Apr 26Apr 22
32°FMay 15May 8May 5Apr 30Apr 27Apr 23Apr 20Apr 17Apr 11
28°FMay 4Apr 26Apr 21Apr 17Apr 14Apr 10Apr 7Apr 4Mar 31
24°FApr 17Apr 11Apr 7Apr 3Apr 1Mar 30Mar 27Mar 23Mar 16
20°FApr 5Mar 31Mar 28Mar 25Mar 21Mar 18Mar 14Mar 9Mar 3
16°FMar 26Mar 21Mar 17Mar 13Mar 9Mar 6Mar 2Feb 26Feb 19

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 30Oct 3Oct 6Oct 9Oct 12Oct 14Oct 17Oct 20Oct 25
32°FOct 8Oct 14Oct 17Oct 20Oct 22Oct 25Oct 28Nov 1Nov 4
28°FOct 19Oct 24Oct 27Oct 31Nov 1Nov 4Nov 7Nov 11Nov 15
24°FOct 31Nov 3Nov 7Nov 10Nov 13Nov 15Nov 19Nov 23Nov 30
20°FNov 9Nov 14Nov 19Nov 22Nov 26Dec 1Dec 4Dec 9Dec 17
16°FNov 21Nov 27Dec 1Dec 6Dec 11Dec 17Dec 22Dec 27Jan 1

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°F176170165160156152148143137
32°F198191187182177173168162156
28°F221214209205201196191184175
24°F248239234229224219214210202
20°F276268261255251246239234226
16°F302294288283276271265259251

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
5,465
Cooling degree days, base 65°F
812
Growing degree days, base 40°F
5,538
Growing degree days, base 45°F
4,303
Growing degree days, base 50°F
3,212
Growing degree days, base 55°F
2,266
Growing degree days, base 60°F
1,462

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09704
February92505
March783031
April4206136
May17553353
June29161582
July2260722
August5225685
September7394472
October35012178
November657036
December94709

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 1.4 km from Donora. 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 USC00362190 (Donora 1 Sw). Public domain.