Addison County climate

Addison County Frost Dates and Growing Season

NOAA 1991-2020 normals for Cornwall, 9.9 km from Addison County, elevation 345 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Cornwall. 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 May 5 and the first fall freeze around October 3, a growing season of about 151 days.

Median at 36°F
last May 18, first September 25
Median at 32°F
last May 5, first October 3
Median at 28°F
last April 26, first October 16

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°FJun 3May 29May 24May 21May 18May 15May 11May 8May 3
32°FMay 20May 15May 11May 8May 5May 2Apr 30Apr 28Apr 23
28°FMay 8May 3Apr 30Apr 28Apr 26Apr 23Apr 20Apr 17Apr 12
24°FApr 26Apr 23Apr 20Apr 17Apr 14Apr 11Apr 8Apr 5Apr 1
20°FApr 17Apr 12Apr 8Apr 6Apr 4Apr 2Mar 31Mar 28Mar 22
16°FApr 8Apr 5Apr 3Apr 1Mar 30Mar 26Mar 23Mar 19Mar 15

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 10Sep 16Sep 19Sep 22Sep 25Sep 27Sep 30Oct 2Oct 6
32°FSep 21Sep 25Sep 29Oct 1Oct 3Oct 5Oct 8Oct 13Oct 19
28°FOct 1Oct 5Oct 9Oct 13Oct 16Oct 19Oct 23Oct 28Nov 1
24°FOct 10Oct 17Oct 22Oct 26Oct 30Nov 1Nov 4Nov 9Nov 14
20°FOct 25Nov 1Nov 4Nov 8Nov 11Nov 13Nov 17Nov 21Nov 27
16°FNov 7Nov 12Nov 15Nov 18Nov 21Nov 25Nov 28Dec 1Dec 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°F148141136132128124120115108
32°F169163158154151147143138131
28°F195187181177173168164159152
24°F218212206202198193187182175
20°F239232227222218215211207200
16°F257250245241237233230225219

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
7,705
Cooling degree days, base 65°F
446
Growing degree days, base 40°F
4,179
Growing degree days, base 45°F
3,173
Growing degree days, base 50°F
2,295
Growing degree days, base 55°F
1,537
Growing degree days, base 60°F
914

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,45201
February1,25200
March1,09105
April658242
May30021222
June8383451
July16171620
August37124552
September18642317
October538276
November86009
December1,23200

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 9.9 km from Addison County. 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 USC00431580 (Cornwall). Public domain.