Dover climate

Dover Frost Dates and Growing Season

NOAA 1991-2020 normals for Rowe 3NE, 23.8 km from Dover, elevation 1735 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rowe 3NE. 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 14 and the first fall freeze around October 4, a growing season of about 143 days.

Median at 36°F
last May 25, first September 23
Median at 32°F
last May 14, first October 4
Median at 28°F
last May 1, first October 14

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 6Jun 2May 29May 27May 25May 22May 19May 15May 10
32°FMay 26May 23May 19May 16May 14May 11May 8May 5Apr 30
28°FMay 16May 11May 8May 4May 1Apr 28Apr 25Apr 21Apr 16
24°FMay 3Apr 27Apr 22Apr 19Apr 15Apr 12Apr 9Apr 5Apr 2
20°FApr 16Apr 10Apr 6Apr 5Apr 3Apr 1Mar 30Mar 26Mar 20
16°FApr 5Apr 1Mar 31Mar 28Mar 25Mar 22Mar 19Mar 16Mar 12

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 11Sep 15Sep 18Sep 20Sep 23Sep 26Sep 30Oct 2Oct 6
32°FSep 20Sep 26Sep 30Oct 1Oct 4Oct 6Oct 9Oct 12Oct 17
28°FOct 1Oct 4Oct 8Oct 11Oct 14Oct 18Oct 21Oct 26Nov 1
24°FOct 9Oct 15Oct 20Oct 24Oct 28Nov 1Nov 3Nov 7Nov 12
20°FOct 22Oct 28Nov 2Nov 5Nov 9Nov 12Nov 16Nov 20Nov 27
16°FNov 4Nov 10Nov 15Nov 19Nov 22Nov 26Nov 29Dec 2Dec 8

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°F139133129125121118114109102
32°F161156151147143139136131124
28°F188181175170165162157152145
24°F216209204199194189184179171
20°F239233229224220216211206199
16°F262255249245242238234228221

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
7,945
Cooling degree days, base 65°F
167
Growing degree days, base 40°F
3,537
Growing degree days, base 45°F
2,572
Growing degree days, base 50°F
1,751
Growing degree days, base 55°F
1,060
Growing degree days, base 60°F
518

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,39500
February1,20500
March1,10800
April714029
May3964131
June14325337
July4874491
August6149452
September22815253
October583049
November87209
December1,19300

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 23.8 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 USC00196989 (Rowe 3NE). Public domain.