Teton County Frost Dates and Growing Season

NOAA 1991-2020 normals for Moran 5WNW, 8.7 km from Teton County, elevation 6805 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Moran 5WNW. 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 8, first September 11

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 25	Jun 20	Jun 15	Jun 11	Jun 8	Jun 3	May 30	May 25	May 19
24°F	Jun 1	May 26	May 20	May 17	May 14	May 11	May 9	May 6	May 2
20°F	May 15	May 10	May 7	May 4	May 3	May 1	Apr 29	Apr 26	Apr 21
16°F	May 4	Apr 30	Apr 28	Apr 25	Apr 22	Apr 20	Apr 18	Apr 15	Apr 10

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 28	Sep 2	Sep 5	Sep 7	Sep 11	Sep 14	Sep 19	Sep 23	Sep 29
24°F	Sep 11	Sep 17	Sep 22	Sep 26	Sep 28	Oct 1	Oct 3	Oct 6	Oct 11
20°F	Sep 26	Oct 1	Oct 4	Oct 6	Oct 10	Oct 13	Oct 16	Oct 19	Oct 24
16°F	Oct 7	Oct 12	Oct 16	Oct 19	Oct 22	Oct 25	Oct 28	Nov 1	Nov 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.

Threshold	10%	20%	30%	40%	50%	60%	70%	80%	90%
36°F	51	44	39	35	32	28	24	21	17
32°F	83	76	70	66	61	57	51	46	38
28°F	120	111	106	101	97	91	85	80	71
24°F	153	147	142	138	133	129	125	119	112
20°F	177	172	167	163	159	155	151	146	139
16°F	199	193	188	185	182	177	174	169	163

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: 10,688
Cooling degree days, base 65°F: 10
Growing degree days, base 40°F: 2,069
Growing degree days, base 45°F: 1,347
Growing degree days, base 50°F: 765
Growing degree days, base 55°F: 338
Growing degree days, base 60°F: 89

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,624	0	0
February	1,352	0	0
March	1,234	0	0
April	936	0	0
May	668	0	15
June	390	0	112
July	176	7	300
August	214	3	260
September	452	0	76
October	842	0	4
November	1,221	0	0
December	1,579	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 8.7 km from Teton County. 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 USC00486440 (Moran 5WNW). Public domain.