Owyhee Frost Dates and Growing Season

NOAA 1991-2020 normals for Wild Horse Rsvr, 42.6 km from Owyhee, elevation 6239 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wild Horse Rsvr. 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 29	Jun 18	Jun 12	Jun 7	Jun 3	May 30	May 25	May 20	May 13
20°F	Jun 3	May 28	May 22	May 18	May 14	May 10	May 6	May 1	Apr 25
16°F	May 16	May 9	May 5	Apr 30	Apr 25	Apr 20	Apr 15	Apr 10	Apr 5

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 29	Sep 2	Sep 5	Sep 7	Sep 10	Sep 13	Sep 16	Sep 20	Sep 24
20°F	Sep 7	Sep 12	Sep 16	Sep 18	Sep 22	Sep 25	Sep 28	Oct 2	Oct 8
16°F	Sep 18	Sep 24	Sep 27	Oct 1	Oct 4	Oct 7	Oct 12	Oct 17	Oct 24

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	32	26	22	19	17	15	13	12	9
32°F	58	50	44	39	35	31	28	24	18
28°F	90	80	74	69	63	59	54	46	37
24°F	123	115	108	102	96	91	85	78	67
20°F	156	147	141	136	131	126	120	113	105
16°F	190	180	173	167	161	156	150	143	133

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: 9,200
Cooling degree days, base 65°F: 63
Growing degree days, base 40°F: 2,587
Growing degree days, base 45°F: 1,752
Growing degree days, base 50°F: 1,087
Growing degree days, base 55°F: 578
Growing degree days, base 60°F: 236

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,432	0	0
February	1,210	0	0
March	1,065	0	0
April	801	0	3
May	580	0	40
June	322	4	165
July	107	37	396
August	140	22	351
September	385	1	120
October	732	0	11
November	1,043	0	0
December	1,386	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 42.6 km from Owyhee. 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 USC00269072 (Wild Horse Rsvr). Public domain.