Delta climate

Delta Frost Dates and Growing Season

NOAA 1991-2020 normals for Conowingo Dam, 15.2 km from Delta, elevation 40 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Conowingo Dam. 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 3 and the first fall freeze around November 6, a growing season of about 217 days.

Median at 36°F
last April 18, first October 28
Median at 32°F
last April 3, first November 6
Median at 28°F
last March 24, first November 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 5Apr 29Apr 24Apr 21Apr 18Apr 15Apr 11Apr 7Apr 3
32°FApr 18Apr 14Apr 9Apr 6Apr 3Apr 1Mar 30Mar 27Mar 22
28°FApr 6Apr 2Mar 31Mar 28Mar 24Mar 21Mar 18Mar 14Mar 8
24°FMar 28Mar 24Mar 20Mar 17Mar 13Mar 10Mar 7Mar 3Feb 27
20°FMar 20Mar 15Mar 10Mar 7Mar 3Feb 28Feb 25Feb 19Feb 11
16°FMar 11Mar 5Mar 1Feb 25Feb 20Feb 15Feb 9Feb 4Jan 28

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 13Oct 19Oct 23Oct 26Oct 28Oct 31Nov 1Nov 4Nov 7
32°FOct 26Oct 30Nov 1Nov 4Nov 6Nov 8Nov 12Nov 14Nov 19
28°FNov 4Nov 8Nov 11Nov 14Nov 17Nov 20Nov 23Nov 27Dec 1
24°FNov 12Nov 16Nov 20Nov 25Nov 29Dec 2Dec 7Dec 14Dec 23
20°FNov 26Dec 2Dec 7Dec 12Dec 19Dec 23Dec 27Jan 1Jan 8
16°FDec 9Dec 19Dec 25Dec 29Jan 2Jan 6Jan 10Jan 16Jan 23

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°F213206201197193188185179172
32°F236229224220217213209205197
28°F261252247243238234230225219
24°F286279272267262258252247238
20°F313305298294289284278270262
16°F335327321315309305301296287

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
99% 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
4,736
Cooling degree days, base 65°F
1,278
Growing degree days, base 40°F
6,350
Growing degree days, base 45°F
5,036
Growing degree days, base 50°F
3,882
Growing degree days, base 55°F
2,876
Growing degree days, base 60°F
2,010

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,00702
February85002
March704129
April34612166
May11274428
June9259700
July0403868
August1346811
September31163582
October25621247
November576040
December84307

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 15.2 km from Delta. 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 USC00182060 (Conowingo Dam). Public domain.