Arapahoe climate

Arapahoe Frost Dates and Growing Season

NOAA 1991-2020 normals for Edison, 10.3 km from Arapahoe, elevation 2120 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Edison. 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 1 and the first fall freeze around October 7, a growing season of about 157 days.

Median at 36°F
last May 9, first September 29
Median at 32°F
last May 1, first October 7
Median at 28°F
last April 21, first October 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 25May 18May 14May 12May 9May 7May 4May 2Apr 28
32°FMay 13May 8May 5May 2May 1Apr 29Apr 25Apr 21Apr 15
28°FMay 5May 1Apr 28Apr 25Apr 21Apr 18Apr 14Apr 10Apr 5
24°FApr 26Apr 20Apr 16Apr 12Apr 8Apr 5Apr 2Mar 30Mar 25
20°FApr 16Apr 10Apr 5Apr 2Mar 31Mar 27Mar 23Mar 18Mar 12
16°FApr 6Apr 1Mar 28Mar 23Mar 19Mar 14Mar 10Mar 7Mar 2

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 20Sep 24Sep 27Sep 29Oct 2Oct 4Oct 7Oct 11
32°FSep 24Sep 27Oct 1Oct 4Oct 7Oct 10Oct 13Oct 16Oct 19
28°FSep 30Oct 6Oct 12Oct 15Oct 17Oct 20Oct 22Oct 25Oct 28
24°FOct 12Oct 18Oct 21Oct 24Oct 26Oct 29Oct 31Nov 3Nov 6
20°FOct 21Oct 26Oct 29Nov 1Nov 3Nov 5Nov 8Nov 10Nov 15
16°FOct 29Nov 2Nov 5Nov 9Nov 11Nov 14Nov 17Nov 21Nov 26

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°F157152148145141138134129123
32°F176168165161157154149145139
28°F200192186182177172168163156
24°F219212207203198194189183175
20°F238231225220215212208202194
16°F259251245240236231225219211

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
6,002
Cooling degree days, base 65°F
983
Growing degree days, base 40°F
5,437
Growing degree days, base 45°F
4,282
Growing degree days, base 50°F
3,261
Growing degree days, base 55°F
2,375
Growing degree days, base 60°F
1,618

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,14100
February95304
March768029
April4615108
May19950339
June20201631
July2335798
August6277736
September105107458
October4268143
November797015
December1,12601

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 10.3 km from Arapahoe. 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 USC00252560 (Edison). Public domain.