West Yellowstone Frost Dates and Growing Season

NOAA 1991-2020 normals for W Yellowstone Gateway, 1.2 km from West Yellowstone, elevation 6679 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for W Yellowstone Gateway. 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.

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	–	–	–	–	–	–	–	–	–
24°F	Jun 21	Jun 14	Jun 10	Jun 5	Jun 1	May 27	May 22	May 16	May 9
20°F	Jun 1	May 22	May 16	May 12	May 8	May 5	May 2	Apr 29	Apr 24
16°F	May 12	May 5	May 1	Apr 29	Apr 26	Apr 22	Apr 18	Apr 15	Apr 11

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	–	–	–	–	–	–	–	–	–
24°F	Aug 26	Sep 1	Sep 4	Sep 7	Sep 11	Sep 14	Sep 17	Sep 21	Sep 26
20°F	Sep 8	Sep 14	Sep 18	Sep 22	Sep 25	Sep 28	Oct 1	Oct 4	Oct 11
16°F	Sep 22	Sep 27	Sep 30	Oct 3	Oct 6	Oct 10	Oct 14	Oct 18	Oct 23

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	30	24	20	18	16	14	12	11	8
32°F	54	47	41	36	33	30	26	23	19
28°F	88	80	74	67	62	56	50	44	37
24°F	127	117	110	105	99	94	89	82	72
20°F	160	151	145	140	135	129	124	118	108
16°F	186	177	173	168	164	159	153	147	138

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: 10,849
Cooling degree days, base 65°F: 16
Growing degree days, base 40°F: 1,989
Growing degree days, base 45°F: 1,276
Growing degree days, base 50°F: 716
Growing degree days, base 55°F: 321
Growing degree days, base 60°F: 97

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,597	0	0
February	1,362	0	0
March	1,259	0	0
April	924	0	1
May	656	0	23
June	416	0	99
July	184	12	297
August	251	4	232
September	492	0	61
October	896	0	4
November	1,241	0	0
December	1,573	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 1.2 km from West Yellowstone. 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 USC00248858 (W Yellowstone Gateway). Public domain.