Dover climate

Dover Frost Dates and Growing Season

NOAA 1991-2020 normals for Dover 1 W, 2.3 km from Dover, elevation 475 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Dover 1 W. 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 4 and the first fall freeze around October 31, a growing season of about 210 days.

Median at 36°F
last April 17, first October 22
Median at 32°F
last April 4, first October 31
Median at 28°F
last March 23, first November 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°FMay 1Apr 27Apr 23Apr 20Apr 17Apr 13Apr 10Apr 7Apr 1
32°FApr 21Apr 15Apr 10Apr 8Apr 4Apr 1Mar 29Mar 24Mar 17
28°FApr 9Apr 3Mar 31Mar 27Mar 23Mar 19Mar 15Mar 9Mar 1
24°FMar 30Mar 23Mar 17Mar 14Mar 10Mar 5Mar 1Feb 25Feb 17
20°FMar 17Mar 12Mar 6Mar 1Feb 26Feb 22Feb 16Feb 11Feb 5
16°FMar 6Feb 28Feb 23Feb 17Feb 11Feb 6Feb 2Jan 29Jan 17

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 10Oct 14Oct 18Oct 20Oct 22Oct 24Oct 26Oct 29Nov 1
32°FOct 18Oct 23Oct 26Oct 29Oct 31Nov 2Nov 5Nov 9Nov 15
28°FOct 31Nov 2Nov 5Nov 8Nov 11Nov 14Nov 18Nov 24Nov 30
24°FNov 8Nov 13Nov 17Nov 21Nov 25Nov 28Dec 1Dec 5Dec 13
20°FNov 17Nov 23Nov 28Dec 1Dec 6Dec 11Dec 17Dec 23Dec 29
16°FNov 28Dec 4Dec 11Dec 18Dec 24Dec 29Jan 3Jan 10Jan 19

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°F207201196191188184180175169
32°F232224219214210205201196190
28°F260251244239234229224218209
24°F286278272267261256249243234
20°F316307299293287281275268259
16°F341332325319313306301293282

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
98% 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
3,845
Cooling degree days, base 65°F
1,539
Growing degree days, base 40°F
7,312
Growing degree days, base 45°F
5,860
Growing degree days, base 50°F
4,553
Growing degree days, base 55°F
3,394
Growing degree days, base 60°F
2,390

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January877021
February684132
March4939122
April22738291
May64131532
June4302748
July0415880
August1394859
September27204627
October21941307
November4894103
December761031

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 2.3 km from Dover. 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 USC00402589 (Dover 1 W). Public domain.