Douglas climate

Douglas Frost Dates and Growing Season

NOAA 1991-2020 normals for Douglas, 0.5 km from Douglas, elevation 4040 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Douglas. 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 March 18 and the first fall freeze around November 13, a growing season of about 235 days.

Median at 36°F
last April 7, first November 3
Median at 32°F
last March 18, first November 13
Median at 28°F
last February 27, first November 25

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°FApr 27Apr 21Apr 16Apr 11Apr 7Apr 5Mar 31Mar 27Mar 18
32°FApr 12Apr 5Mar 31Mar 25Mar 18Mar 14Mar 10Mar 4Feb 27
28°FMar 24Mar 12Mar 6Mar 2Feb 27Feb 22Feb 16Feb 9Jan 31
24°FMar 3Feb 23Feb 15Feb 8Feb 3Jan 31Jan 25Jan 17Jan 5
20°FFeb 13Feb 3Jan 26Jan 18Jan 11Jan 6Jan 1Dec 25Dec 14
16°FFeb 6Jan 24Jan 11Jan 7Jan 3Dec 29Dec 24Dec 17Dec 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°FOct 20Oct 25Oct 29Nov 1Nov 3Nov 5Nov 9Nov 13Nov 19
32°FOct 27Nov 1Nov 5Nov 10Nov 13Nov 16Nov 20Nov 24Nov 30
28°FNov 5Nov 12Nov 18Nov 21Nov 25Nov 29Dec 2Dec 5Dec 9
24°FNov 15Nov 25Nov 30Dec 3Dec 6Dec 8Dec 12Dec 18Dec 23
20°FNov 28Dec 4Dec 9Dec 15Dec 18Dec 22Dec 27Jan 3Jan 12
16°FDec 3Dec 14Dec 18Dec 23Dec 27Jan 1Jan 6Jan 11Jan 29

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°F230221216212207202197191183
32°F264253246240235229224216204
28°F300289281274268262254246235
24°F336327317310303296289279270
20°F365362353346339333327317304
16°F365365365365365365362349331

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
84% of years
16°F or colder
37% 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
2,136
Cooling degree days, base 65°F
1,989
Growing degree days, base 40°F
8,993
Growing degree days, base 45°F
7,234
Growing degree days, base 50°F
5,618
Growing degree days, base 55°F
4,204
Growing degree days, base 60°F
2,998

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January525039
February370093
March2693213
April9639394
May10199654
June0432882
July0488953
August0436901
September1305754
October5283496
November2784197
December535041

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 0.5 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 USC00022659 (Douglas). Public domain.