Dover climate

Dover Frost Dates and Growing Season

NOAA 1991-2020 normals for Rochester Intl AP, 29.3 km from Dover, elevation 1304 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Rochester Intl AP. 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 6, a growing season of about 159 days.

Median at 36°F
last May 9, first September 28
Median at 32°F
last April 30, first October 6
Median at 28°F
last April 18, first October 17

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 21May 18May 14May 12May 9May 7May 5May 2Apr 28
32°FMay 13May 8May 5May 2Apr 30Apr 28Apr 24Apr 21Apr 15
28°FMay 2Apr 29Apr 25Apr 22Apr 18Apr 15Apr 12Apr 8Apr 4
24°FApr 24Apr 19Apr 15Apr 11Apr 9Apr 6Apr 4Apr 1Mar 24
20°FApr 16Apr 10Apr 6Apr 4Apr 2Mar 30Mar 26Mar 21Mar 15
16°FApr 8Apr 3Mar 31Mar 29Mar 25Mar 20Mar 17Mar 13Mar 9

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 14Sep 19Sep 22Sep 25Sep 28Oct 1Oct 3Oct 6Oct 11
32°FSep 22Sep 27Oct 1Oct 4Oct 6Oct 9Oct 12Oct 16Oct 20
28°FOct 4Oct 8Oct 12Oct 15Oct 17Oct 20Oct 23Oct 26Oct 31
24°FOct 13Oct 19Oct 22Oct 25Oct 28Oct 30Nov 2Nov 5Nov 11
20°FOct 23Oct 28Nov 1Nov 2Nov 5Nov 7Nov 11Nov 15Nov 19
16°FNov 1Nov 4Nov 8Nov 11Nov 14Nov 17Nov 20Nov 23Nov 28

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°F158153148144140137134129122
32°F178171167163159156152147140
28°F201194189184180177172167161
24°F221213208204200195191185179
20°F238231226221217213209203197
16°F252245240236232228223218212

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
7,856
Cooling degree days, base 65°F
533
Growing degree days, base 40°F
4,433
Growing degree days, base 45°F
3,415
Growing degree days, base 50°F
2,511
Growing degree days, base 55°F
1,721
Growing degree days, base 60°F
1,054

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,55800
February1,29600
March1,034111
April596260
May26332262
June49126527
July14186637
August30128563
September17053345
October534696
November941010
December1,37000

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 29.3 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 USW00014925 (Rochester Intl AP). Public domain.