Darby climate

Darby Frost Dates and Growing Season

NOAA 1991-2020 normals for Darby, 0.4 km from Darby, elevation 3880 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Darby. 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 24 and the first fall freeze around September 23, a growing season of about 118 days.

Median at 36°F
last June 16, first September 6
Median at 32°F
last May 24, first September 23
Median at 28°F
last May 5, first October 4

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°FJul 4Jun 28Jun 23Jun 19Jun 16Jun 12Jun 8Jun 4May 28
32°FJun 14Jun 7Jun 2May 28May 24May 19May 15May 11May 6
28°FMay 21May 14May 11May 7May 5May 2Apr 30Apr 28Apr 23
24°FMay 7May 2Apr 30Apr 27Apr 24Apr 21Apr 17Apr 12Apr 5
20°FApr 25Apr 19Apr 14Apr 8Apr 3Mar 30Mar 24Mar 16Mar 8
16°FApr 8Mar 30Mar 22Mar 16Mar 11Mar 7Mar 2Feb 28Feb 19

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°FAug 20Aug 27Sep 1Sep 3Sep 6Sep 9Sep 14Sep 19Sep 25
32°FSep 4Sep 10Sep 16Sep 20Sep 23Sep 26Sep 30Oct 4Oct 8
28°FSep 18Sep 24Sep 28Oct 1Oct 4Oct 6Oct 10Oct 14Oct 19
24°FOct 1Oct 4Oct 8Oct 13Oct 16Oct 20Oct 23Oct 28Nov 2
20°FOct 8Oct 16Oct 21Oct 26Oct 30Nov 1Nov 5Nov 10Nov 17
16°FOct 20Oct 28Nov 1Nov 5Nov 9Nov 13Nov 17Nov 21Nov 27

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°F1059791868076706455
32°F14313613012411811310710092
28°F170162157153150145140134124
24°F200190184179174170165161153
20°F238226219212206200195186177
16°F269260253246239233226218206

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
7,589
Cooling degree days, base 65°F
178
Growing degree days, base 40°F
3,371
Growing degree days, base 45°F
2,392
Growing degree days, base 50°F
1,583
Growing degree days, base 55°F
940
Growing degree days, base 60°F
472

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19200
February99300
March86403
April675022
May4212123
June22314250
July6991487
August8961438
September2669216
October627044
November95402
December1,21800

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 0.4 km from Darby. 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 USC00242221 (Darby). Public domain.