Friday Harbor climate

Friday Harbor Frost Dates and Growing Season

NOAA 1991-2020 normals for Friday Harbor AP, 1.4 km from Friday Harbor, elevation 109 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Friday Harbor AP. 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 26 and the first fall freeze around November 10, a growing season of about 230 days.

Median at 36°F
last April 29, first October 24
Median at 32°F
last March 26, first November 10
Median at 28°F
last February 22, 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°FMay 16May 10May 6May 2Apr 29Apr 26Apr 21Apr 15Apr 7
32°FApr 21Apr 10Apr 4Mar 31Mar 26Mar 18Mar 12Mar 4Feb 25
28°FMar 18Mar 9Mar 2Feb 27Feb 22Feb 16Feb 10Jan 27Jan 9
24°FFeb 28Feb 21Feb 13Feb 1Jan 22Jan 13Jan 4Dec 26Dec 9
20°FFeb 15Jan 26Jan 18Jan 9Jan 1Dec 27Dec 18Dec 9Nov 30
16°FJan 19Jan 14Jan 7Jan 2Dec 31Dec 22Dec 14Dec 7Nov 26

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 17Oct 21Oct 24Oct 28Nov 1Nov 4Nov 11
32°FOct 21Oct 29Nov 2Nov 6Nov 10Nov 15Nov 20Nov 26Dec 1
28°FNov 7Nov 14Nov 22Nov 27Dec 1Dec 8Dec 16Dec 26Jan 7
24°FNov 21Nov 30Dec 6Dec 14Dec 20Dec 29Jan 7Jan 18Feb 3
20°FNov 27Dec 5Dec 10Dec 18Dec 24Jan 1Jan 9Jan 18Jan 31
16°FNov 24Dec 4Dec 13Dec 20Dec 28Jan 1Jan 6Jan 14Jan 18

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°F208197190184178173168163154
32°F265254243236230224218209197
28°F331314305298289280270260248
24°F365365353345334326316307291
20°F365365365365365365356343330
16°F365365365365365365365365364

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
78% of years
20°F or colder
38% of years
16°F or colder
14% 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
5,171
Cooling degree days, base 65°F
32
Growing degree days, base 40°F
4,118
Growing degree days, base 45°F
2,615
Growing degree days, base 50°F
1,470
Growing degree days, base 55°F
667
Growing degree days, base 60°F
184

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January71002
February63002
March605010
April479034
May3410136
June2075248
July13012347
August11612361
September2133240
October426075
November588014
December72702

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 1.4 km from Friday 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 USW00094276 (Friday Harbor AP). Public domain.