Clinton climate

Clinton Frost Dates and Growing Season

NOAA 1991-2020 normals for Rockville, 18.5 km from Clinton, elevation 689 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rockville. 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 30 and the first fall freeze around October 12, a growing season of about 164 days.

Median at 36°F
last May 10, first October 2
Median at 32°F
last April 30, first October 12
Median at 28°F
last April 18, first October 22

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 27May 20May 16May 14May 10May 7May 4Apr 30Apr 25
32°FMay 15May 10May 6May 2Apr 30Apr 26Apr 23Apr 19Apr 14
28°FMay 5Apr 30Apr 25Apr 22Apr 18Apr 15Apr 12Apr 8Apr 4
24°FApr 23Apr 17Apr 12Apr 8Apr 5Apr 2Mar 31Mar 27Mar 21
20°FApr 10Apr 4Apr 1Mar 30Mar 27Mar 23Mar 19Mar 15Mar 8
16°FMar 31Mar 27Mar 22Mar 19Mar 15Mar 12Mar 8Mar 4Feb 26

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

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°F164158153148144140135130123
32°F184176172168164161156151142
28°F206199194190185181177172164
24°F233225219215210206200194186
20°F257248243238234229223217210
16°F280271265259255250245239231

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
5,635
Cooling degree days, base 65°F
917
Growing degree days, base 40°F
5,708
Growing degree days, base 45°F
4,491
Growing degree days, base 50°F
3,402
Growing degree days, base 55°F
2,438
Growing degree days, base 60°F
1,605

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19502
February95605
March752248
April38012166
May14572399
June20199628
July3279741
August5231691
September79107480
October34916194
November698142
December1,05406

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 18.5 km from Clinton. 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 USC00127522 (Rockville). Public domain.