Copper River Census Area Frost Dates and Growing Season

NOAA 1991-2020 normals for Gennallen Kcam, 8 km from Copper River Census Area, elevation 1383 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Gennallen Kcam. 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 29, first September 1

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 13	Jun 6	Jun 3	May 31	May 29	May 27	May 23	May 19	May 13
24°F	May 30	May 25	May 20	May 16	May 13	May 11	May 8	May 4	Apr 29
20°F	May 16	May 10	May 7	May 4	May 1	Apr 29	Apr 27	Apr 23	Apr 18
16°F	May 5	Apr 30	Apr 28	Apr 24	Apr 21	Apr 17	Apr 15	Apr 12	Apr 9

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 14	Aug 21	Aug 27	Aug 30	Sep 1	Sep 4	Sep 8	Sep 13	Sep 18
24°F	Aug 29	Sep 3	Sep 5	Sep 9	Sep 14	Sep 18	Sep 22	Sep 26	Sep 30
20°F	Sep 8	Sep 15	Sep 19	Sep 22	Sep 25	Sep 28	Oct 1	Oct 4	Oct 9
16°F	Sep 18	Sep 23	Sep 26	Sep 29	Oct 1	Oct 4	Oct 7	Oct 10	Oct 16

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	60	51	45	40	36	32	28	24	19
32°F	89	80	75	67	61	57	50	44	37
28°F	114	106	102	97	92	88	83	76	66
24°F	142	135	130	125	120	116	111	105	97
20°F	164	157	153	148	144	141	136	131	124
16°F	181	174	170	166	162	158	155	150	143

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: 13,813
Cooling degree days, base 65°F: 13
Growing degree days, base 40°F: 1,717
Growing degree days, base 45°F: 1,062
Growing degree days, base 50°F: 556
Growing degree days, base 55°F: 226
Growing degree days, base 60°F: 65

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Cooling DD	Growing DD 50
January	2,175	0	0
February	1,732	0	0
March	1,610	0	0
April	990	0	0
May	629	0	24
June	330	3	149
July	235	8	245
August	369	1	126
September	648	0	11
October	1,206	0	1
November	1,797	0	0
December	2,093	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 8 km from Copper River Census Area. 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 USC00503304 (Gennallen Kcam). Public domain.