Idaho County Frost Dates and Growing Season

NOAA 1991-2020 normals for Elk City 1NE, 1 km from Idaho County, elevation 4058 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Elk City 1NE. 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 May 22, first September 7

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 12	May 31	May 28	May 24	May 22	May 18	May 16	May 12	May 7
24°F	May 22	May 17	May 13	May 9	May 7	May 4	May 2	Apr 29	Apr 24
20°F	May 7	May 3	Apr 30	Apr 25	Apr 19	Apr 14	Apr 10	Apr 5	Apr 1
16°F	Apr 13	Apr 7	Apr 4	Apr 1	Mar 29	Mar 25	Mar 20	Mar 17	Mar 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	Aug 22	Aug 28	Sep 1	Sep 3	Sep 7	Sep 10	Sep 13	Sep 17	Sep 23
24°F	Sep 7	Sep 13	Sep 17	Sep 20	Sep 24	Sep 28	Oct 1	Oct 7	Oct 18
20°F	Sep 23	Sep 29	Oct 3	Oct 8	Oct 15	Oct 20	Oct 26	Oct 30	Nov 6
16°F	Oct 4	Oct 15	Oct 23	Oct 29	Nov 1	Nov 5	Nov 9	Nov 14	Nov 20

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	45	38	34	31	28	25	22	20	17
32°F	92	83	76	70	64	58	51	45	38
28°F	127	120	115	109	105	101	96	89	77
24°F	164	155	149	144	138	134	129	124	116
20°F	208	198	191	185	179	173	167	158	149
16°F	240	233	226	221	216	210	205	198	188

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: 8,358
Cooling degree days, base 65°F: 69
Growing degree days, base 40°F: 2,736
Growing degree days, base 45°F: 1,854
Growing degree days, base 50°F: 1,152
Growing degree days, base 55°F: 617
Growing degree days, base 60°F: 257

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,245	0	0
February	1,030	0	0
March	958	0	0
April	745	0	6
May	529	0	63
June	294	6	188
July	117	40	390
August	145	21	345
September	357	1	138
October	671	0	20
November	986	0	0
December	1,282	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 Idaho 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 USC00102875 (Elk City 1NE). Public domain.