Oak Harbor climate

Oak Harbor Frost Dates and Growing Season

NOAA 1991-2020 normals for Whidbey Island Nas, 6.6 km from Oak Harbor, elevation 47 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Whidbey Island Nas. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around March 13 and the first fall freeze around November 14, a growing season of about 244 days.

Median at 36°F
last April 9, first October 28
Median at 32°F
last March 13, first November 14
Median at 28°F
last February 18, first December 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.

Threshold10%20%30%40%50%60%70%80%90%
36°FApr 29Apr 21Apr 17Apr 13Apr 9Apr 6Apr 2Mar 29Mar 22
32°FApr 1Mar 27Mar 21Mar 17Mar 13Mar 9Mar 3Feb 27Feb 20
28°FMar 12Mar 2Feb 27Feb 22Feb 18Feb 13Feb 4Jan 24Jan 5
24°FFeb 24Feb 16Feb 10Feb 2Jan 24Jan 10Jan 2Dec 23Dec 8
20°FFeb 16Feb 4Jan 25Jan 9Dec 31Dec 23Dec 15Dec 7Nov 30
16°FFeb 4Jan 24Jan 16Jan 1Dec 30Dec 24Dec 15Dec 7Nov 30

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.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 6Oct 13Oct 18Oct 24Oct 28Oct 31Nov 3Nov 9Nov 17
32°FOct 26Nov 1Nov 6Nov 10Nov 14Nov 19Nov 23Nov 28Dec 5
28°FNov 9Nov 16Nov 22Nov 26Dec 1Dec 5Dec 11Dec 21Jan 6
24°FNov 19Nov 26Dec 1Dec 7Dec 15Dec 23Jan 1Jan 13Feb 2
20°FNov 25Dec 1Dec 7Dec 15Dec 22Dec 30Jan 10Jan 26Feb 9
16°FNov 27Dec 6Dec 10Dec 21Dec 27Dec 31Jan 9Jan 19Jan 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.

Threshold10%20%30%40%50%60%70%80%90%
36°F226217210205200194188182173
32°F277265258250244239233227217
28°F331318307299290282275266255
24°F365365356343334326317308294
20°F365365365365365364347334319
16°F365365365365365365365365358

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
99% of years
24°F or colder
82% of years
20°F or colder
43% of years
16°F or colder
15% 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
4,727
Cooling degree days, base 65°F
25
Growing degree days, base 40°F
4,536
Growing degree days, base 45°F
2,949
Growing degree days, base 50°F
1,664
Growing degree days, base 55°F
744
Growing degree days, base 60°F
198

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January660013
February58409
March549025
April423061
May3100160
June1932260
July1178357
August11111366
September1983255
October3750116
November534034
December67409

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 6.6 km from Oak Harbor. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USW00024255 (Whidbey Island Nas). Public domain.