Derby climate

Derby Frost Dates and Growing Season

NOAA 1991-2020 normals for Denver-Stapleton, 9.4 km from Derby, elevation 5286 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Denver-Stapleton. 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 4 and the first fall freeze around October 8, a growing season of about 156 days.

Median at 36°F
last May 12, first October 1
Median at 32°F
last May 4, first October 8
Median at 28°F
last April 22, first October 18

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 26May 21May 18May 15May 12May 10May 8May 5May 2
32°FMay 16May 11May 8May 6May 4May 2Apr 29Apr 24Apr 20
28°FMay 7May 2Apr 30Apr 25Apr 22Apr 19Apr 16Apr 12Apr 6
24°FApr 27Apr 21Apr 17Apr 14Apr 10Apr 6Apr 3Mar 31Mar 23
20°FApr 18Apr 10Apr 5Apr 1Mar 29Mar 24Mar 19Mar 14Mar 8
16°FApr 7Mar 31Mar 25Mar 20Mar 15Mar 10Mar 6Mar 2Feb 24

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 16Sep 22Sep 25Sep 28Oct 1Oct 3Oct 6Oct 8Oct 13
32°FSep 25Sep 30Oct 3Oct 6Oct 8Oct 11Oct 14Oct 17Oct 20
28°FOct 3Oct 8Oct 12Oct 15Oct 18Oct 21Oct 23Oct 27Oct 31
24°FOct 12Oct 18Oct 21Oct 24Oct 27Oct 30Nov 2Nov 7Nov 12
20°FOct 20Oct 25Oct 31Nov 3Nov 6Nov 10Nov 14Nov 18Nov 22
16°FOct 27Nov 3Nov 7Nov 12Nov 16Nov 19Nov 23Nov 26Dec 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°F156150147143140136132127121
32°F175169164160156153149145138
28°F198191185180177173168164158
24°F223216210204200195190184176
20°F245237232226221215210205197
16°F270260253247241235230223213

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
5,765
Cooling degree days, base 65°F
813
Growing degree days, base 40°F
5,263
Growing degree days, base 45°F
4,049
Growing degree days, base 50°F
3,011
Growing degree days, base 55°F
2,136
Growing degree days, base 60°F
1,404

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,02201
February88504
March721029
April508184
May25726270
June46151556
July4306767
August10244699
September10883434
October4313140
November746026
December1,02902

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 9.4 km from Derby. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00023062 (Denver-Stapleton). Public domain.