Wainwright Frost Dates and Growing Season

NOAA 1991-2020 normals for Wainwright AP, 1.6 km from Wainwright, elevation 30 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Wainwright 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.

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	–	–	–	–	–	–	–	–	–
24°F	Jun 7	Jun 5	Jun 3	Jun 2	May 31	May 29	May 25	May 22	May 17
20°F	Jun 1	May 29	May 27	May 24	May 21	May 19	May 17	May 15	May 11
16°F	May 25	May 22	May 20	May 17	May 16	May 14	May 12	May 10	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	–	–	–	–	–	–	–	–	–
24°F	Sep 2	Sep 13	Sep 18	Sep 21	Sep 23	Sep 25	Sep 28	Oct 1	Oct 4
20°F	Sep 22	Sep 26	Sep 28	Oct 1	Oct 2	Oct 4	Oct 7	Oct 10	Oct 14
16°F	Sep 29	Oct 2	Oct 5	Oct 7	Oct 10	Oct 12	Oct 15	Oct 17	Oct 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	44	35	28	23	19	16	12	10	8
32°F	77	66	57	50	43	37	31	25	20
28°F	108	102	96	92	87	80	72	65	52
24°F	130	125	121	118	114	111	107	102	92
20°F	147	143	139	136	133	130	127	123	117
16°F	161	156	153	149	147	144	141	137	133

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: 18,265
Cooling degree days, base 65°F: 0
Growing degree days, base 40°F: 433
Growing degree days, base 45°F: 189
Growing degree days, base 50°F: 61
Growing degree days, base 55°F: 12
Growing degree days, base 60°F: 1

Growing degree days by month, base 50°F

Heating and cooling by month

Month	Heating DD	Growing DD 50
January	2,348	0
February	2,141	0
March	2,345	0
April	1,837	0
May	1,266	0
June	767	9
July	605	33
August	677	18
September	903	1
October	1,369	0
November	1,788	0
December	2,220	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 1.6 km from Wainwright. 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 USW00027503 (Wainwright AP). Public domain.