Washington climate

Washington Frost Dates and Growing Season

NOAA 1991-2020 normals for Washington, 1.1 km from Washington, elevation 1305 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Washington. 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 April 24 and the first fall freeze around October 14, a growing season of about 171 days.

Median at 36°F
last May 2, first October 4
Median at 32°F
last April 24, first October 14
Median at 28°F
last April 14, first October 23

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 11May 8May 5May 2Apr 30Apr 28Apr 24Apr 20
32°FMay 8May 4Apr 30Apr 27Apr 24Apr 21Apr 18Apr 15Apr 10
28°FApr 28Apr 24Apr 21Apr 17Apr 14Apr 11Apr 7Apr 4Mar 31
24°FApr 20Apr 14Apr 9Apr 6Apr 3Mar 31Mar 29Mar 24Mar 18
20°FApr 10Apr 5Apr 1Mar 30Mar 27Mar 22Mar 18Mar 13Mar 8
16°FApr 2Mar 28Mar 23Mar 18Mar 15Mar 11Mar 7Mar 3Feb 27

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 20Sep 26Sep 29Oct 2Oct 4Oct 7Oct 9Oct 12Oct 16
32°FSep 29Oct 3Oct 8Oct 11Oct 14Oct 17Oct 19Oct 22Oct 25
28°FOct 9Oct 14Oct 18Oct 20Oct 23Oct 25Oct 28Oct 31Nov 4
24°FOct 19Oct 23Oct 27Oct 30Nov 1Nov 3Nov 6Nov 9Nov 14
20°FOct 27Nov 1Nov 3Nov 6Nov 8Nov 12Nov 16Nov 20Nov 27
16°FNov 2Nov 7Nov 11Nov 15Nov 19Nov 22Nov 26Dec 1Dec 5

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°F171165160157154151147142137
32°F190183179175171167163159152
28°F210204199195191187183178170
24°F233225220215210207202197189
20°F252244238233229224219214207
16°F272264257252247242238231223

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
5,704
Cooling degree days, base 65°F
1,314
Growing degree days, base 40°F
6,098
Growing degree days, base 45°F
4,893
Growing degree days, base 50°F
3,815
Growing degree days, base 55°F
2,857
Growing degree days, base 60°F
2,022

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,20600
February96606
March732147
April39911157
May13784420
June11277717
July1427891
August3343804
September72149530
October34421211
November738131
December1,09702

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 1.1 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 USC00148578 (Washington). Public domain.