West Dennis climate

West Dennis Frost Dates and Growing Season

NOAA 1991-2020 normals for W Harwich, 4.7 km from West Dennis, elevation 15 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for W Harwich. 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 13 and the first fall freeze around November 3, a growing season of about 204 days.

Median at 36°F
last April 27, first October 22
Median at 32°F
last April 13, first November 3
Median at 28°F
last April 1, first November 17

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

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 8Oct 13Oct 17Oct 19Oct 22Oct 25Oct 27Oct 31Nov 5
32°FOct 22Oct 26Oct 29Nov 1Nov 3Nov 6Nov 9Nov 13Nov 18
28°FNov 2Nov 7Nov 11Nov 14Nov 17Nov 20Nov 23Nov 28Dec 4
24°FNov 16Nov 21Nov 25Nov 29Dec 1Dec 4Dec 8Dec 13Dec 19
20°FNov 26Dec 1Dec 5Dec 9Dec 13Dec 18Dec 22Dec 26Jan 1
16°FDec 7Dec 13Dec 19Dec 22Dec 26Dec 30Jan 2Jan 7Jan 15

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°F197191186181177173169165158
32°F223217212208204200197192186
28°F251244238234230226222218211
24°F277271265261256252247242236
20°F301292286282278274269263256
16°F321313306302298294289283278

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
5,761
Cooling degree days, base 65°F
466
Growing degree days, base 40°F
4,679
Growing degree days, base 45°F
3,495
Growing degree days, base 50°F
2,502
Growing degree days, base 55°F
1,659
Growing degree days, base 60°F
982

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,04600
February95200
March86300
April590019
May3181163
June7042423
July4193654
August5177637
September8451417
October3412161
November606028
December88301

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 4.7 km from West Dennis. 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 USC00199227 (W Harwich). Public domain.