Wilton climate

Wilton Frost Dates and Growing Season

NOAA 1991-2020 normals for Stamford 5 N, 12 km from Wilton, elevation 190 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Stamford 5 N. 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 17 and the first fall freeze around October 23, a growing season of about 188 days.

Median at 36°F
last April 30, first October 12
Median at 32°F
last April 17, first October 23
Median at 28°F
last April 3, first November 2

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 16May 10May 7May 3Apr 30Apr 28Apr 24Apr 20Apr 16
32°FMay 2Apr 27Apr 23Apr 19Apr 17Apr 14Apr 12Apr 8Apr 3
28°FApr 19Apr 12Apr 8Apr 6Apr 3Apr 1Mar 30Mar 26Mar 20
24°FApr 5Apr 2Mar 30Mar 28Mar 24Mar 21Mar 18Mar 15Mar 9
20°FMar 28Mar 23Mar 19Mar 16Mar 14Mar 11Mar 8Mar 4Feb 27
16°FMar 21Mar 15Mar 11Mar 7Mar 4Mar 1Feb 26Feb 22Feb 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°FOct 1Oct 4Oct 6Oct 9Oct 12Oct 14Oct 17Oct 21Oct 25
32°FOct 8Oct 12Oct 16Oct 19Oct 23Oct 26Oct 29Nov 1Nov 6
28°FOct 18Oct 24Oct 28Oct 31Nov 2Nov 5Nov 9Nov 13Nov 19
24°FOct 31Nov 5Nov 10Nov 13Nov 17Nov 20Nov 24Nov 29Dec 4
20°FNov 13Nov 19Nov 23Nov 28Dec 1Dec 4Dec 7Dec 12Dec 18
16°FNov 28Dec 2Dec 6Dec 11Dec 15Dec 19Dec 22Dec 27Jan 2

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°F183177171167163160156151144
32°F208201196192188184180175168
28°F233226221216212208204198192
24°F261253247242237232228223215
20°F286277272267263257253247239
16°F309301295289284279274269261

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
5,358
Cooling degree days, base 65°F
858
Growing degree days, base 40°F
5,552
Growing degree days, base 45°F
4,312
Growing degree days, base 50°F
3,227
Growing degree days, base 55°F
2,286
Growing degree days, base 60°F
1,494

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,08201
February91702
March783013
April4226116
May16343348
June27152575
July1298762
August3251713
September7098479
October3349178
November627036
December93005

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 12 km from Wilton. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00067970 (Stamford 5 N). Public domain.