Irwinton climate

Irwinton Frost Dates and Growing Season

NOAA 1991-2020 normals for Irwinton 4 Wnw, 6.5 km from Irwinton, elevation 515 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Irwinton 4 Wnw. 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 12 and the first fall freeze around November 19, a growing season of about 255 days.

Median at 36°F
last March 29, first November 6
Median at 32°F
last March 12, first November 19
Median at 28°F
last February 25, first December 4

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 12Apr 7Apr 3Apr 1Mar 29Mar 24Mar 19Mar 14Mar 5
32°FApr 1Mar 26Mar 19Mar 15Mar 12Mar 7Mar 2Feb 26Feb 18
28°FMar 18Mar 11Mar 6Mar 1Feb 25Feb 18Feb 13Feb 6Jan 29
24°FMar 5Feb 25Feb 16Feb 8Feb 3Jan 31Jan 27Jan 18Jan 6
20°FFeb 23Feb 11Feb 4Jan 31Jan 27Jan 22Jan 15Jan 8Dec 28
16°FFeb 13Feb 2Jan 29Jan 25Jan 20Jan 15Jan 9Jan 2Dec 28

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 25Oct 29Nov 1Nov 3Nov 6Nov 10Nov 13Nov 18Nov 25
32°FNov 3Nov 7Nov 12Nov 15Nov 19Nov 23Nov 29Dec 4Dec 15
28°FNov 12Nov 20Nov 25Dec 1Dec 4Dec 10Dec 19Dec 29Jan 6
24°FNov 25Dec 2Dec 8Dec 17Dec 24Jan 1Jan 6Jan 13Jan 26
20°FDec 7Dec 17Dec 26Jan 1Jan 8Jan 13Jan 18Jan 26Feb 5
16°FDec 22Dec 29Jan 3Jan 8Jan 14Jan 18Jan 23Jan 30Feb 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°F253244237232226221216210204
32°F286275267261255250244238228
28°F319307299293285278273263252
24°F354341332324316309302293280
20°F365365363352344336329320307
16°F365365365365365365351341328

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
94% of years
20°F or colder
70% of years
16°F or colder
34% 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
2,241
Cooling degree days, base 65°F
2,183
Growing degree days, base 40°F
9,140
Growing degree days, base 45°F
7,448
Growing degree days, base 50°F
5,881
Growing degree days, base 55°F
4,474
Growing degree days, base 60°F
3,240

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January570171
February425297
March26517248
April10368419
May10235690
June0408858
July0522987
August0476941
September2331778
October79105493
November30014200
December487499

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 6.5 km from Irwinton. 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 USC00094594 (Irwinton 4 Wnw). Public domain.