Washington climate

Washington Frost Dates and Growing Season

NOAA 1991-2020 normals for Washington, 2.2 km from Washington, elevation 687 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 28 and the first fall freeze around October 11, a growing season of about 165 days.

Median at 36°F
last May 6, first October 1
Median at 32°F
last April 28, first October 11
Median at 28°F
last April 17, first October 22

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 19May 14May 11May 9May 6May 3May 1Apr 28Apr 24
32°FMay 11May 6May 3Apr 30Apr 28Apr 24Apr 21Apr 18Apr 13
28°FMay 2Apr 27Apr 23Apr 20Apr 17Apr 13Apr 10Apr 8Apr 3
24°FApr 21Apr 15Apr 10Apr 8Apr 6Apr 3Apr 1Mar 29Mar 22
20°FApr 10Apr 5Apr 2Mar 31Mar 28Mar 24Mar 20Mar 15Mar 9
16°FApr 1Mar 27Mar 23Mar 19Mar 16Mar 13Mar 10Mar 7Mar 2

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 17Sep 21Sep 25Sep 28Oct 1Oct 3Oct 5Oct 9Oct 13
32°FSep 25Oct 1Oct 4Oct 8Oct 11Oct 13Oct 16Oct 19Oct 24
28°FOct 7Oct 13Oct 16Oct 19Oct 22Oct 24Oct 26Oct 29Nov 1
24°FOct 19Oct 23Oct 26Oct 28Oct 31Nov 1Nov 4Nov 8Nov 13
20°FOct 29Nov 1Nov 3Nov 5Nov 8Nov 11Nov 15Nov 19Nov 25
16°FNov 3Nov 7Nov 11Nov 14Nov 17Nov 21Nov 25Nov 30Dec 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°F164159155151147143140136129
32°F186179174170165161157152147
28°F206200194191187183178172165
24°F229221216212208204199195188
20°F251242237232228224220214208
16°F272263257252248243239234227

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
6,536
Cooling degree days, base 65°F
867
Growing degree days, base 40°F
5,291
Growing degree days, base 45°F
4,164
Growing degree days, base 50°F
3,155
Growing degree days, base 55°F
2,264
Growing degree days, base 60°F
1,497

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,36800
February1,11602
March857127
April4646114
May18257352
June22190618
July3284746
August10226682
September11090435
October41513157
November804023
December1,18601

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 2.2 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 USC00138688 (Washington). Public domain.