Washington climate

Washington Frost Dates and Growing Season

NOAA 1991-2020 normals for Washington, 3.7 km from Washington, elevation 487 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 8 and the first fall freeze around October 25, a growing season of about 199 days.

Median at 36°F
last April 20, first October 16
Median at 32°F
last April 8, first October 25
Median at 28°F
last March 29, first November 4

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 5Apr 29Apr 25Apr 22Apr 20Apr 17Apr 15Apr 11Apr 7
32°FApr 22Apr 17Apr 13Apr 10Apr 8Apr 5Apr 2Mar 31Mar 24
28°FApr 11Apr 7Apr 3Apr 1Mar 29Mar 25Mar 21Mar 17Mar 12
24°FApr 1Mar 28Mar 23Mar 20Mar 17Mar 15Mar 11Mar 6Feb 28
20°FMar 23Mar 18Mar 14Mar 12Mar 8Mar 5Mar 2Feb 27Feb 20
16°FMar 17Mar 12Mar 8Mar 4Mar 1Feb 26Feb 21Feb 15Feb 7

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 2Oct 8Oct 11Oct 14Oct 16Oct 18Oct 21Oct 24Oct 27
32°FOct 13Oct 16Oct 19Oct 22Oct 25Oct 27Oct 29Nov 1Nov 5
28°FOct 22Oct 26Oct 30Nov 1Nov 4Nov 5Nov 9Nov 14Nov 21
24°FNov 1Nov 5Nov 8Nov 12Nov 16Nov 19Nov 24Nov 29Dec 5
20°FNov 9Nov 15Nov 20Nov 25Nov 28Dec 1Dec 5Dec 10Dec 16
16°FNov 20Nov 26Nov 30Dec 5Dec 9Dec 14Dec 18Dec 23Dec 28

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°F195189184180177173169165159
32°F220213207203199195191186180
28°F243235229224221216212206200
24°F268259253248243239234229222
20°F288280275268264259254248241
16°F311301295290284279273266257

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
4,966
Cooling degree days, base 65°F
1,298
Growing degree days, base 40°F
6,389
Growing degree days, base 45°F
5,100
Growing degree days, base 50°F
3,948
Growing degree days, base 55°F
2,935
Growing degree days, base 60°F
2,050

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,08303
February857013
March655363
April31517209
May107107468
June6266711
July1392857
August2339803
September62143531
October30029236
November630248
December94806

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 3.7 km from Washington. 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 USC00238746 (Washington). Public domain.