Douglas climate

Douglas Frost Dates and Growing Season

NOAA 1991-2020 normals for Douglas 1 Se, 2.3 km from Douglas, elevation 4870 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Douglas 1 Se. 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 19 and the first fall freeze around September 23, a growing season of about 126 days.

Median at 36°F
last June 1, first September 13
Median at 32°F
last May 19, first September 23
Median at 28°F
last May 7, first October 3

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 15Jun 10Jun 6Jun 4Jun 1May 30May 27May 23May 19
32°FJun 2May 29May 25May 22May 19May 16May 14May 10May 7
28°FMay 21May 16May 13May 10May 7May 5May 2Apr 30Apr 24
24°FMay 9May 5May 1Apr 29Apr 26Apr 23Apr 19Apr 15Apr 10
20°FMay 1Apr 26Apr 21Apr 17Apr 14Apr 10Apr 6Apr 2Mar 27
16°FApr 21Apr 14Apr 10Apr 6Apr 3Mar 31Mar 26Mar 22Mar 14

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 31Sep 5Sep 8Sep 11Sep 13Sep 16Sep 19Sep 22Sep 27
32°FSep 10Sep 14Sep 18Sep 21Sep 23Sep 26Sep 29Oct 2Oct 6
28°FSep 18Sep 23Sep 27Sep 30Oct 3Oct 5Oct 9Oct 12Oct 16
24°FSep 27Oct 2Oct 6Oct 10Oct 13Oct 15Oct 19Oct 21Oct 25
20°FOct 3Oct 10Oct 14Oct 18Oct 21Oct 23Oct 26Oct 29Nov 1
16°FOct 11Oct 18Oct 22Oct 25Oct 28Oct 31Nov 3Nov 7Nov 12

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°F123116112108104100969083
32°F144138133129126122118114107
28°F167161156151147143139134126
24°F189181176172168164161155148
20°F212204198193188183179172165
16°F231224217212207203198192183

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
7,255
Cooling degree days, base 65°F
488
Growing degree days, base 40°F
4,199
Growing degree days, base 45°F
3,151
Growing degree days, base 50°F
2,267
Growing degree days, base 55°F
1,541
Growing degree days, base 60°F
949

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,21801
February1,08000
March879012
April635035
May3717165
June9770426
July12217669
August26164603
September20630298
October606050
November90507
December1,22001

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 2.3 km from Douglas. 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 USC00482685 (Douglas 1 Se). Public domain.