Sedro-Woolley climate

Sedro-Woolley Frost Dates and Growing Season

NOAA 1991-2020 normals for Sedro-Woolley, 0.9 km from Sedro-Woolley, elevation 60 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Sedro-Woolley. 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 27 and the first fall freeze around November 6, a growing season of about 224 days.

Median at 36°F
last April 22, first October 17
Median at 32°F
last March 27, first November 6
Median at 28°F
last March 1, first November 24

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 11May 5May 1Apr 26Apr 22Apr 18Apr 13Apr 8Apr 1
32°FApr 17Apr 7Apr 3Mar 31Mar 27Mar 23Mar 19Mar 13Mar 8
28°FMar 22Mar 14Mar 9Mar 5Mar 1Feb 26Feb 22Feb 16Feb 2
24°FMar 2Feb 26Feb 20Feb 13Feb 4Jan 30Jan 19Jan 9Dec 25
20°FFeb 20Feb 6Jan 31Jan 22Jan 13Jan 6Dec 31Dec 21Dec 10
16°FFeb 1Jan 20Jan 11Jan 3Dec 31Dec 24Dec 18Dec 10Dec 1

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 1Oct 5Oct 9Oct 13Oct 17Oct 22Oct 26Nov 1Nov 8
32°FOct 15Oct 23Oct 28Nov 1Nov 6Nov 11Nov 16Nov 21Nov 28
28°FNov 1Nov 9Nov 15Nov 19Nov 24Nov 28Dec 2Dec 10Dec 19
24°FNov 18Nov 25Nov 30Dec 5Dec 11Dec 17Dec 23Dec 31Jan 14
20°FNov 26Dec 2Dec 11Dec 18Dec 24Dec 30Jan 4Jan 15Feb 1
16°FNov 28Dec 6Dec 13Dec 19Dec 24Dec 30Jan 2Jan 13Jan 26

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°F204196189183178172166159149
32°F253243236229224218211205195
28°F302290280274268261255246235
24°F354340329321312304297287275
20°F365365364356347339332321309
16°F365365365365365365362350336

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
97% of years
20°F or colder
70% of years
16°F or colder
33% 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
5,070
Cooling degree days, base 65°F
86
Growing degree days, base 40°F
4,376
Growing degree days, base 45°F
2,933
Growing degree days, base 50°F
1,803
Growing degree days, base 55°F
960
Growing degree days, base 60°F
381

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January76404
February64803
March608014
April456054
May2893187
June1689291
July7134428
August6334436
September1757283
October422086
November615015
December79002

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 0.9 km from Sedro-Woolley. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00457507 (Sedro-Woolley). Public domain.