Wilton climate

Wilton Frost Dates and Growing Season

NOAA 1991-2020 normals for Muscatine 2N, 13.3 km from Wilton, elevation 680 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Muscatine 2N. 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 22, a growing season of about 184 days.

Median at 36°F
last April 30, first October 12
Median at 32°F
last April 18, first October 22
Median at 28°F
last April 7, first October 31

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 14May 9May 5May 3Apr 30Apr 28Apr 24Apr 20Apr 15
32°FMay 2Apr 30Apr 25Apr 21Apr 18Apr 15Apr 11Apr 9Apr 4
28°FApr 23Apr 18Apr 13Apr 10Apr 7Apr 5Apr 2Mar 31Mar 25
24°FApr 13Apr 7Apr 3Apr 1Mar 31Mar 27Mar 23Mar 18Mar 12
20°FApr 3Mar 31Mar 26Mar 22Mar 18Mar 16Mar 12Mar 9Mar 4
16°FMar 26Mar 21Mar 18Mar 14Mar 11Mar 9Mar 6Mar 2Feb 25

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 27Oct 2Oct 6Oct 9Oct 12Oct 14Oct 17Oct 19Oct 23
32°FOct 8Oct 13Oct 17Oct 19Oct 22Oct 24Oct 26Oct 29Nov 2
28°FOct 19Oct 23Oct 26Oct 29Oct 31Nov 1Nov 4Nov 8Nov 13
24°FOct 29Nov 1Nov 3Nov 6Nov 8Nov 11Nov 14Nov 18Nov 23
20°FNov 4Nov 9Nov 12Nov 15Nov 18Nov 21Nov 25Nov 29Dec 4
16°FNov 11Nov 16Nov 20Nov 23Nov 27Dec 1Dec 3Dec 7Dec 13

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°F184177173169164160155151143
32°F203196192188184180177172165
28°F225218213209205201195192185
24°F247239234229225220216211204
20°F266259254248243240235230223
16°F282274269264260255250245238

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
6,284
Cooling degree days, base 65°F
897
Growing degree days, base 40°F
5,429
Growing degree days, base 45°F
4,277
Growing degree days, base 50°F
3,248
Growing degree days, base 55°F
2,335
Growing degree days, base 60°F
1,548

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,32400
February1,07803
March840231
April4528125
May17656357
June21189618
July3290752
August8231688
September93105465
October38216178
November761030
December1,14702

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 13.3 km from Wilton. 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 USC00135844 (Muscatine 2N). Public domain.