Jackson Frost Dates and Growing Season

NOAA 1991-2020 normals for Jackson, 0.7 km from Jackson, elevation 6210 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jackson. 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 9, first September 4

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	Jul 1	Jun 25	Jun 19	Jun 14	Jun 9	Jun 5	Jun 1	May 28	May 23
24°F	Jun 4	May 30	May 25	May 22	May 19	May 16	May 13	May 10	May 4
20°F	May 21	May 16	May 12	May 9	May 6	May 3	Apr 30	Apr 26	Apr 19
16°F	May 12	May 5	May 1	Apr 26	Apr 21	Apr 17	Apr 11	Apr 6	Mar 30

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 19	Aug 26	Aug 31	Sep 2	Sep 4	Sep 7	Sep 10	Sep 14	Sep 20
24°F	Sep 1	Sep 6	Sep 10	Sep 14	Sep 17	Sep 20	Sep 24	Sep 28	Oct 3
20°F	Sep 14	Sep 19	Sep 23	Sep 27	Sep 30	Oct 3	Oct 6	Oct 11	Oct 17
16°F	Sep 27	Oct 3	Oct 7	Oct 12	Oct 16	Oct 19	Oct 22	Oct 26	Oct 31

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	25	22	20	18	16	14	12
32°F	73	64	58	51	46	42	38	33	27
28°F	108	101	96	91	85	81	76	69	60
24°F	142	134	129	125	120	116	111	105	98
20°F	170	162	156	151	146	142	138	132	124
16°F	200	193	187	182	176	171	164	158	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: 9,857
Cooling degree days, base 65°F: 22
Growing degree days, base 40°F: 2,315
Growing degree days, base 45°F: 1,516
Growing degree days, base 50°F: 880
Growing degree days, base 55°F: 414
Growing degree days, base 60°F: 129

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,513	0	0
February	1,264	0	0
March	1,110	0	0
April	810	0	2
May	592	0	35
June	337	1	150
July	160	13	320
August	197	8	281
September	437	0	84
October	784	0	8
November	1,149	0	0
December	1,503	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 0.7 km from Jackson. 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 USC00484910 (Jackson). Public domain.