Washington climate

Washington Frost Dates and Growing Season

NOAA 1991-2020 normals for Washington Is, 5.1 km from Washington, elevation 686 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Washington Is. 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 May 15 and the first fall freeze around October 14, a growing season of about 152 days.

Median at 36°F
last May 28, first October 2
Median at 32°F
last May 15, first October 14
Median at 28°F
last May 3, first October 28

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°FJun 10Jun 5Jun 2May 31May 28May 25May 22May 18May 13
32°FMay 31May 26May 21May 18May 15May 12May 9May 5Apr 30
28°FMay 18May 13May 9May 6May 3Apr 30Apr 28Apr 24Apr 20
24°FMay 5May 1Apr 27Apr 24Apr 20Apr 18Apr 15Apr 11Apr 6
20°FApr 21Apr 17Apr 13Apr 10Apr 8Apr 5Apr 2Mar 31Mar 25
16°FApr 11Apr 6Apr 3Apr 1Mar 30Mar 27Mar 23Mar 20Mar 14

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°FSep 19Sep 24Sep 27Sep 30Oct 2Oct 5Oct 8Oct 12Oct 16
32°FSep 28Oct 2Oct 7Oct 11Oct 14Oct 18Oct 21Oct 25Oct 31
28°FOct 10Oct 17Oct 21Oct 25Oct 28Oct 31Nov 3Nov 6Nov 10
24°FOct 24Oct 29Nov 1Nov 4Nov 7Nov 10Nov 14Nov 18Nov 22
20°FNov 2Nov 8Nov 12Nov 15Nov 18Nov 20Nov 24Nov 28Dec 3
16°FNov 13Nov 18Nov 21Nov 24Nov 27Nov 30Dec 3Dec 7Dec 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.

Threshold10%20%30%40%50%60%70%80%90%
36°F147140135131127123119114107
32°F174166160156152148143137129
28°F196189184180176172167162155
24°F221214208203199195190185178
20°F243236231226223219214209203
16°F264256252247242238235230224

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
8,264
Cooling degree days, base 65°F
210
Growing degree days, base 40°F
3,469
Growing degree days, base 45°F
2,531
Growing degree days, base 50°F
1,734
Growing degree days, base 55°F
1,074
Growing degree days, base 60°F
555

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,44900
February1,28500
March1,15000
April79204
May478177
June16918302
July4786504
August4583504
September19422287
October551056
November88202
December1,22100

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 5.1 km from Washington. 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 USC00478905 (Washington Is). Public domain.