Prudhoe Bay Frost Dates and Growing Season

NOAA 1991-2020 normals for Deadhorse AP, 8.8 km from Prudhoe Bay, elevation 61 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Deadhorse AP. 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 9, first September 2

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 22	Jun 17	Jun 15	Jun 12	Jun 9	Jun 7	Jun 5	Jun 2	May 30
24°F	Jun 9	Jun 5	Jun 3	Jun 2	May 31	May 29	May 26	May 23	May 19
20°F	Jun 1	May 30	May 27	May 24	May 22	May 20	May 18	May 16	May 12
16°F	May 27	May 22	May 20	May 18	May 16	May 15	May 13	May 11	May 7

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 26	Aug 30	Sep 2	Sep 6	Sep 11	Sep 16	Sep 20
24°F	Aug 29	Sep 6	Sep 12	Sep 17	Sep 19	Sep 21	Sep 24	Sep 27	Oct 1
20°F	Sep 14	Sep 20	Sep 23	Sep 26	Sep 28	Sep 30	Oct 2	Oct 5	Oct 9
16°F	Sep 24	Sep 27	Sep 30	Oct 2	Oct 4	Oct 6	Oct 8	Oct 11	Oct 14

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	38	31	27	23	20	18	16	13	11
32°F	72	65	58	52	47	43	38	31	26
28°F	106	99	92	87	82	78	73	67	59
24°F	128	122	118	114	110	106	102	96	88
20°F	143	138	134	130	128	125	121	118	111
16°F	153	148	145	142	139	136	134	130	124

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: 18,823
Cooling degree days, base 65°F: 0
Growing degree days, base 40°F: 499
Growing degree days, base 45°F: 242
Growing degree days, base 50°F: 96
Growing degree days, base 55°F: 30
Growing degree days, base 60°F: 6

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Growing DD 50
January	2,475	0
February	2,233	0
March	2,443	0
April	1,864	0
May	1,283	0
June	753	18
July	548	54
August	665	24
September	911	1
October	1,448	0
November	1,899	0
December	2,302	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 8.8 km from Prudhoe Bay. 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 USW00027406 (Deadhorse AP). Public domain.