Dover climate

Dover Frost Dates and Growing Season

NOAA 1991-2020 normals for Durham, 8.7 km from Dover, elevation 75 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Durham. 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 8 and the first fall freeze around October 4, a growing season of about 148 days.

Median at 36°F
last May 20, first September 26
Median at 32°F
last May 8, first October 4
Median at 28°F
last April 27, first October 15

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 2May 29May 26May 23May 20May 18May 15May 11May 7
32°FMay 22May 18May 14May 11May 8May 6May 3Apr 30Apr 27
28°FMay 10May 4May 2Apr 29Apr 27Apr 24Apr 22Apr 18Apr 13
24°FApr 25Apr 20Apr 17Apr 14Apr 10Apr 8Apr 6Apr 3Mar 31
20°FApr 11Apr 7Apr 5Apr 2Apr 1Mar 30Mar 27Mar 22Mar 17
16°FApr 3Mar 31Mar 28Mar 25Mar 22Mar 19Mar 16Mar 13Mar 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°FSep 12Sep 17Sep 20Sep 23Sep 26Sep 28Oct 1Oct 3Oct 6
32°FSep 23Sep 28Oct 1Oct 2Oct 4Oct 7Oct 10Oct 14Oct 20
28°FOct 2Oct 6Oct 9Oct 13Oct 15Oct 19Oct 23Oct 27Nov 2
24°FOct 13Oct 18Oct 22Oct 26Oct 30Nov 1Nov 5Nov 8Nov 14
20°FOct 27Nov 1Nov 5Nov 9Nov 12Nov 15Nov 18Nov 22Nov 28
16°FNov 12Nov 17Nov 20Nov 23Nov 26Nov 29Dec 1Dec 4Dec 9

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°F145140135131128125121116111
32°F164159155152148145142137131
28°F191184180176172168164158152
24°F217212208203199194189184177
20°F245238233228225221216212206
16°F268262257252248244239234226

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
6,793
Cooling degree days, base 65°F
501
Growing degree days, base 40°F
4,458
Growing degree days, base 45°F
3,377
Growing degree days, base 50°F
2,445
Growing degree days, base 55°F
1,653
Growing degree days, base 60°F
1,000

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,28201
February1,08800
March95206
April577255
May29117211
June7886458
July10191646
August20151597
September14551360
October472295
November774014
December1,10501

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 8.7 km from Dover. 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 USC00272174 (Durham). Public domain.