Powell County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ovando 9 Sse, 9.6 km from Powell County, elevation 4325 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ovando 9 Sse. 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 26, 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 18	Jun 7	Jun 2	May 30	May 26	May 23	May 20	May 16	May 11
24°F	May 23	May 18	May 15	May 12	May 9	May 7	May 5	May 3	Apr 30
20°F	May 9	May 6	May 3	May 1	Apr 30	Apr 27	Apr 24	Apr 19	Apr 12
16°F	Apr 30	Apr 26	Apr 22	Apr 18	Apr 13	Apr 8	Apr 3	Mar 31	Mar 23

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 30	Sep 2	Sep 5	Sep 8	Sep 11	Sep 14	Sep 17	Sep 20	Sep 25
24°F	Sep 9	Sep 15	Sep 19	Sep 21	Sep 24	Sep 27	Sep 30	Oct 2	Oct 6
20°F	Sep 20	Sep 24	Sep 28	Oct 1	Oct 3	Oct 6	Oct 9	Oct 13	Oct 18
16°F	Sep 28	Oct 2	Oct 6	Oct 10	Oct 15	Oct 19	Oct 22	Oct 26	Nov 1

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	52	45	39	35	31	28	25	22	18
32°F	94	86	80	73	67	62	56	50	42
28°F	129	121	116	111	108	103	98	92	82
24°F	154	148	143	139	136	132	128	122	116
20°F	179	172	167	162	158	155	151	147	141
16°F	213	203	197	191	185	180	176	170	161

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: 9,521
Cooling degree days, base 65°F: 43
Growing degree days, base 40°F: 2,456
Growing degree days, base 45°F: 1,648
Growing degree days, base 50°F: 998
Growing degree days, base 55°F: 514
Growing degree days, base 60°F: 196

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	1,440	0	0
February	1,240	0	0
March	1,048	0	0
April	793	0	2
May	546	0	57
June	322	2	156
July	139	24	352
August	171	16	318
September	420	1	106
October	815	0	8
November	1,137	0	0
December	1,451	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 9.6 km from Powell 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 USC00246304 (Ovando 9 Sse). Public domain.