Upper Saint Clair climate

Upper Saint Clair Frost Dates and Growing Season

NOAA 1991-2020 normals for Pittsburgh Allegheny CO AP, 13.8 km from Upper Saint Clair, elevation 1248 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Pittsburgh Allegheny CO 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 18 and the first fall freeze around October 28, a growing season of about 193 days.

Median at 36°F
last April 29, first October 17
Median at 32°F
last April 18, first October 28
Median at 28°F
last April 5, first November 8

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 17May 10May 6May 1Apr 29Apr 26Apr 23Apr 20Apr 16
32°FMay 6Apr 28Apr 24Apr 21Apr 18Apr 15Apr 11Apr 7Apr 2
28°FApr 21Apr 16Apr 12Apr 8Apr 5Apr 3Apr 1Mar 28Mar 23
24°FApr 8Apr 4Apr 1Mar 30Mar 28Mar 25Mar 21Mar 17Mar 12
20°FMar 31Mar 27Mar 24Mar 20Mar 17Mar 15Mar 11Mar 7Feb 28
16°FMar 23Mar 18Mar 15Mar 12Mar 8Mar 5Feb 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°FOct 4Oct 8Oct 12Oct 14Oct 17Oct 20Oct 22Oct 24Oct 29
32°FOct 14Oct 19Oct 22Oct 25Oct 28Oct 31Nov 2Nov 5Nov 10
28°FOct 28Nov 1Nov 3Nov 5Nov 8Nov 11Nov 14Nov 17Nov 22
24°FNov 5Nov 10Nov 12Nov 15Nov 18Nov 21Nov 26Nov 30Dec 5
20°FNov 12Nov 18Nov 23Nov 28Dec 1Dec 5Dec 9Dec 16Dec 23
16°FNov 23Nov 30Dec 5Dec 11Dec 16Dec 20Dec 24Dec 29Jan 5

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°F188182177173169165162157150
32°F212206201197193189185180171
28°F238230225221216213209204196
24°F262253246241237233228224217
20°F286277270264259254248243234
16°F308298292287282277271265256

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
5,407
Cooling degree days, base 65°F
826
Growing degree days, base 40°F
5,632
Growing degree days, base 45°F
4,390
Growing degree days, base 50°F
3,286
Growing degree days, base 55°F
2,318
Growing degree days, base 60°F
1,491

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10206
February921010
March765141
April39611158
May15759375
June26161585
July2267730
August6224684
September7888462
October34914186
November654040
December95009

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 13.8 km from Upper Saint Clair. 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 USW00014762 (Pittsburgh Allegheny CO AP). Public domain.