Derry climate

Derry Frost Dates and Growing Season

NOAA 1991-2020 normals for W Hampstead, 10.7 km from Derry, elevation 288 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for W Hampstead. 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 11, a growing season of about 162 days.

Median at 36°F
last May 13, first October 1
Median at 32°F
last April 30, first October 11
Median at 28°F
last April 18, first October 24

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 25May 21May 18May 16May 13May 11May 8May 5May 1
32°FMay 14May 9May 5May 3Apr 30Apr 28Apr 25Apr 23Apr 20
28°FMay 1Apr 26Apr 23Apr 21Apr 18Apr 16Apr 13Apr 10Apr 5
24°FApr 18Apr 14Apr 9Apr 7Apr 5Apr 3Apr 1Mar 31Mar 25
20°FApr 5Apr 2Apr 1Mar 30Mar 28Mar 24Mar 21Mar 18Mar 13
16°FMar 31Mar 28Mar 24Mar 21Mar 18Mar 16Mar 13Mar 9Mar 4

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 19Sep 24Sep 27Sep 30Oct 1Oct 3Oct 5Oct 9Oct 14
32°FSep 29Oct 3Oct 5Oct 8Oct 11Oct 14Oct 18Oct 21Oct 27
28°FOct 8Oct 12Oct 17Oct 21Oct 24Oct 27Oct 31Nov 2Nov 7
24°FOct 20Oct 27Oct 31Nov 2Nov 5Nov 8Nov 11Nov 15Nov 19
20°FNov 3Nov 8Nov 11Nov 15Nov 17Nov 20Nov 23Nov 28Dec 2
16°FNov 15Nov 21Nov 25Nov 28Dec 1Dec 3Dec 6Dec 9Dec 16

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°F158152148145141137133129123
32°F182175170165162159155150144
28°F205199195191187183179175167
24°F230223218215211209205201194
20°F257250244240236232228223216
16°F279272266262258253249245239

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
6,746
Cooling degree days, base 65°F
497
Growing degree days, base 40°F
4,453
Growing degree days, base 45°F
3,373
Growing degree days, base 50°F
2,437
Growing degree days, base 55°F
1,647
Growing degree days, base 60°F
995

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,26800
February1,07801
March95208
April580250
May29214212
June7686462
July10196651
August20147592
September14950354
October472291
November762015
December1,09001

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 10.7 km from Derry. 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 USC00279278 (W Hampstead). Public domain.