Mineral County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hermit 8 Se, 17.5 km from Mineral County, elevation 8950 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hermit 8 Se. 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 11, first September 13

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 27	Jun 21	Jun 17	Jun 14	Jun 11	Jun 8	Jun 6	Jun 3	May 30
24°F	Jun 11	Jun 6	Jun 3	May 31	May 28	May 24	May 21	May 17	May 13
20°F	May 30	May 22	May 17	May 13	May 10	May 7	May 4	May 1	Apr 27
16°F	May 11	May 4	May 2	Apr 29	Apr 26	Apr 22	Apr 19	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	Aug 31	Sep 5	Sep 8	Sep 11	Sep 13	Sep 15	Sep 18	Sep 22	Sep 26
24°F	Sep 12	Sep 16	Sep 20	Sep 23	Sep 25	Sep 28	Oct 1	Oct 3	Oct 7
20°F	Sep 22	Sep 27	Oct 1	Oct 3	Oct 6	Oct 9	Oct 12	Oct 16	Oct 20
16°F	Oct 3	Oct 8	Oct 12	Oct 16	Oct 18	Oct 20	Oct 23	Oct 27	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	49	41	36	33	29	26	23	19	16
32°F	81	76	71	67	62	58	53	47	38
28°F	110	104	99	95	92	88	84	78	70
24°F	138	131	127	123	120	116	111	107	100
20°F	167	161	157	152	149	145	139	134	127
16°F	195	188	183	179	175	170	165	162	154

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: 9,830
Cooling degree days, base 65°F: 6
Growing degree days, base 40°F: 2,285
Growing degree days, base 45°F: 1,460
Growing degree days, base 50°F: 814
Growing degree days, base 55°F: 349
Growing degree days, base 60°F: 84

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,507	0	0
February	1,275	0	0
March	1,149	0	0
April	854	0	1
May	619	0	18
June	335	0	140
July	158	4	313
August	223	1	248
September	414	0	89
October	739	0	6
November	1,085	0	0
December	1,474	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 17.5 km from Mineral 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 USC00053951 (Hermit 8 Se). Public domain.