Golden climate

Golden Frost Dates and Growing Season

NOAA 1991-2020 normals for Ralston Rsvr, 8.3 km from Golden, elevation 5900 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ralston Rsvr. 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 3 and the first fall freeze around October 14, a growing season of about 161 days.

Median at 36°F
last May 12, first October 5
Median at 32°F
last May 3, first October 14
Median at 28°F
last April 25, first October 23

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 27May 22May 18May 15May 12May 10May 7May 4Apr 30
32°FMay 17May 13May 9May 6May 3May 1Apr 29Apr 26Apr 21
28°FMay 8May 3Apr 30Apr 28Apr 25Apr 21Apr 17Apr 13Apr 7
24°FApr 30Apr 24Apr 19Apr 15Apr 11Apr 7Apr 3Mar 31Mar 23
20°FApr 20Apr 13Apr 7Apr 2Mar 31Mar 26Mar 21Mar 14Mar 6
16°FApr 11Apr 2Mar 28Mar 23Mar 16Mar 11Mar 6Mar 1Feb 22

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 20Sep 27Sep 30Oct 2Oct 5Oct 7Oct 10Oct 14Oct 18
32°FSep 30Oct 4Oct 7Oct 10Oct 14Oct 17Oct 20Oct 24Oct 28
28°FOct 7Oct 13Oct 17Oct 20Oct 23Oct 27Oct 30Nov 2Nov 6
24°FOct 15Oct 21Oct 26Oct 30Nov 2Nov 5Nov 8Nov 12Nov 16
20°FOct 21Oct 29Nov 2Nov 5Nov 9Nov 13Nov 16Nov 20Nov 25
16°FOct 30Nov 5Nov 11Nov 14Nov 17Nov 21Nov 24Nov 28Dec 4

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°F161154150146143139135130123
32°F182175170165161157153147140
28°F203196190186182178174168160
24°F225216212207202197192186177
20°F252241234227221215211204194
16°F271263256250244237229221211

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
5,642
Cooling degree days, base 65°F
751
Growing degree days, base 40°F
5,225
Growing degree days, base 45°F
3,989
Growing degree days, base 50°F
2,937
Growing degree days, base 55°F
2,056
Growing degree days, base 60°F
1,327

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January95503
February86306
March724034
April523283
May27925258
June57140534
July6277736
August14220671
September12081422
October4206151
November711036
December96804

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 8.3 km from Golden. 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 USC00056816 (Ralston Rsvr). Public domain.