Crested Butte Frost Dates and Growing Season

NOAA 1991-2020 normals for Crested Butte, 1 km from Crested Butte, elevation 8868 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Crested Butte. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

NOAA does not state freeze dates for this station.

Median at 28°F: last June 14, first September 8

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Jun 29	Jun 24	Jun 20	Jun 17	Jun 14	Jun 11	Jun 9	Jun 6	Jun 2
24°F	Jun 8	Jun 4	May 31	May 27	May 23	May 20	May 17	May 13	May 8
20°F	May 20	May 15	May 12	May 9	May 6	May 4	May 2	Apr 30	Apr 25
16°F	May 7	May 4	May 1	Apr 29	Apr 26	Apr 23	Apr 20	Apr 17	Apr 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	–	–	–	–	–	–	–	–	–
32°F	–	–	–	–	–	–	–	–	–
28°F	Aug 26	Sep 1	Sep 3	Sep 5	Sep 8	Sep 10	Sep 12	Sep 15	Sep 18
24°F	Sep 7	Sep 12	Sep 15	Sep 17	Sep 20	Sep 22	Sep 24	Sep 28	Oct 1
20°F	Sep 19	Sep 24	Sep 26	Sep 29	Oct 1	Oct 3	Oct 6	Oct 9	Oct 14
16°F	Sep 30	Oct 4	Oct 6	Oct 9	Oct 13	Oct 16	Oct 19	Oct 22	Oct 27

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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	34	28	24	20	18	15	14	12	10
32°F	69	62	57	52	47	43	38	32	27
28°F	102	95	91	87	83	79	75	70	63
24°F	136	130	126	122	118	114	110	104	96
20°F	164	157	153	149	145	142	138	134	128
16°F	186	180	176	172	168	164	161	156	150

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: 11,209
Cooling degree days, base 65°F: 1
Growing degree days, base 40°F: 1,900
Growing degree days, base 45°F: 1,165
Growing degree days, base 50°F: 589
Growing degree days, base 55°F: 199
Growing degree days, base 60°F: 30

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,716	0	0
February	1,438	0	0
March	1,319	0	0
April	960	0	0
May	670	0	12
June	392	0	97
July	224	1	244
August	281	0	190
September	494	0	46
October	832	0	1
November	1,220	0	0
December	1,665	0	0

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 1 km from Crested Butte. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00051959 (Crested Butte). Public domain.