Delaware climate

Delaware Frost Dates and Growing Season

NOAA 1991-2020 normals for Marysville, 20.6 km from Delaware, elevation 970 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Marysville. 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 19 and the first fall freeze around October 26, a growing season of about 188 days.

Median at 36°F
last April 30, first October 14
Median at 32°F
last April 19, first October 26
Median at 28°F
last April 7, first November 6

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 15May 9May 6May 3Apr 30Apr 27Apr 24Apr 20Apr 17
32°FMay 5Apr 29Apr 25Apr 22Apr 19Apr 17Apr 13Apr 10Apr 5
28°FApr 22Apr 18Apr 14Apr 11Apr 7Apr 4Apr 1Mar 29Mar 23
24°FApr 12Apr 5Apr 2Mar 31Mar 28Mar 24Mar 21Mar 17Mar 11
20°FMar 31Mar 27Mar 23Mar 20Mar 17Mar 13Mar 10Mar 6Feb 28
16°FMar 22Mar 17Mar 13Mar 10Mar 6Mar 3Feb 28Feb 23Feb 13

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 30Oct 4Oct 8Oct 12Oct 14Oct 17Oct 20Oct 23Oct 27
32°FOct 13Oct 18Oct 21Oct 24Oct 26Oct 29Oct 31Nov 3Nov 7
28°FOct 25Oct 31Nov 1Nov 4Nov 6Nov 9Nov 12Nov 15Nov 21
24°FNov 4Nov 7Nov 11Nov 14Nov 17Nov 21Nov 25Nov 30Dec 4
20°FNov 11Nov 16Nov 21Nov 25Nov 29Dec 2Dec 6Dec 11Dec 20
16°FNov 23Nov 29Dec 2Dec 6Dec 10Dec 16Dec 20Dec 25Jan 1

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°F186180175171166163158153146
32°F208200196191188184180175168
28°F232225219215211207203199191
24°F258251245240235231227222215
20°F282274268262257252248241233
16°F307297291285279275269263254

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
5,546
Cooling degree days, base 65°F
968
Growing degree days, base 40°F
5,734
Growing degree days, base 45°F
4,513
Growing degree days, base 50°F
3,424
Growing degree days, base 55°F
2,468
Growing degree days, base 60°F
1,647

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,15303
February95505
March770138
April40010151
May14776399
June19207637
July1300764
August5251711
September75108484
October34314188
November681037
December99706

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 20.6 km from Delaware. 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 USC00334979 (Marysville). Public domain.