Contoocook climate

Contoocook Frost Dates and Growing Season

NOAA 1991-2020 normals for Hopkinton Lake, 4.5 km from Contoocook, elevation 430 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hopkinton Lake. 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 6 and the first fall freeze around October 1, a growing season of about 146 days.

Median at 36°F
last May 20, first September 23
Median at 32°F
last May 6, first October 1
Median at 28°F
last April 27, first October 11

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 30May 26May 23May 20May 17May 14May 10May 6
32°FMay 20May 16May 12May 9May 6May 4May 2Apr 30Apr 27
28°FMay 8May 4May 1Apr 30Apr 27Apr 25Apr 23Apr 21Apr 17
24°FApr 28Apr 24Apr 21Apr 18Apr 15Apr 13Apr 10Apr 7Apr 4
20°FApr 17Apr 13Apr 9Apr 6Apr 4Apr 3Apr 1Mar 30Mar 23
16°FApr 6Apr 3Apr 1Mar 30Mar 27Mar 23Mar 20Mar 16Mar 13

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 14Sep 17Sep 20Sep 23Sep 25Sep 28Oct 1Oct 4
32°FSep 20Sep 24Sep 28Sep 30Oct 1Oct 3Oct 6Oct 9Oct 13
28°FSep 30Oct 2Oct 5Oct 8Oct 11Oct 15Oct 18Oct 22Oct 28
24°FOct 8Oct 14Oct 18Oct 21Oct 25Oct 28Nov 1Nov 4Nov 8
20°FOct 22Oct 27Nov 1Nov 3Nov 6Nov 9Nov 12Nov 16Nov 21
16°FNov 2Nov 8Nov 12Nov 15Nov 18Nov 22Nov 25Nov 30Dec 4

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°F142136132129125122118112107
32°F162157153150146143139134128
28°F185178174170166163160156150
24°F210204199195190187183179172
20°F234227222218214211206202195
16°F258251245241237232228223216

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
7,215
Cooling degree days, base 65°F
429
Growing degree days, base 40°F
4,219
Growing degree days, base 45°F
3,189
Growing degree days, base 50°F
2,294
Growing degree days, base 55°F
1,534
Growing degree days, base 60°F
903

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,32500
February1,16600
March1,03107
April623039
May29811207
June8473441
July11174627
August24126567
September17543325
October516271
November81609
December1,14700

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 4.5 km from Contoocook. 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 USC00274218 (Hopkinton Lake). Public domain.