Washington climate

Washington Frost Dates and Growing Season

NOAA 1991-2020 normals for Washington Wwtp 4W, 1.9 km from Washington, elevation 10 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Washington Wwtp 4W. 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 22 and the first fall freeze around November 15, a growing season of about 237 days.

Median at 36°F
last April 3, first November 5
Median at 32°F
last March 22, first November 15
Median at 28°F
last March 8, first November 27

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°FApr 19Apr 13Apr 9Apr 6Apr 3Mar 31Mar 28Mar 24Mar 18
32°FApr 7Apr 1Mar 29Mar 25Mar 22Mar 19Mar 16Mar 12Mar 5
28°FMar 27Mar 20Mar 16Mar 13Mar 8Mar 4Feb 28Feb 24Feb 15
24°FMar 15Mar 7Mar 2Feb 27Feb 22Feb 16Feb 9Feb 2Jan 25
20°FMar 1Feb 22Feb 14Feb 6Jan 31Jan 28Jan 21Jan 13Jan 2
16°FFeb 12Feb 3Jan 31Jan 26Jan 21Jan 17Jan 12Jan 6Dec 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°FOct 26Oct 30Nov 1Nov 3Nov 5Nov 7Nov 10Nov 13Nov 19
32°FNov 3Nov 6Nov 9Nov 12Nov 15Nov 18Nov 21Nov 26Dec 1
28°FNov 11Nov 15Nov 19Nov 23Nov 27Dec 1Dec 4Dec 10Dec 23
24°FNov 23Nov 29Dec 3Dec 7Dec 13Dec 22Dec 29Jan 3Jan 14
20°FDec 6Dec 14Dec 22Dec 29Jan 3Jan 9Jan 15Jan 22Feb 1
16°FDec 18Dec 29Jan 3Jan 8Jan 13Jan 17Jan 22Jan 28Feb 3

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°F236229224219215212208204198
32°F262252247242237233228223216
28°F294283276271265259254247239
24°F331319311304297291284276266
20°F365355346336332324316308297
16°F365365365365365360348339329

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
99% of years
20°F or colder
87% of years
16°F or colder
51% 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
2,913
Cooling degree days, base 65°F
1,813
Growing degree days, base 40°F
8,204
Growing degree days, base 45°F
6,607
Growing degree days, base 50°F
5,166
Growing degree days, base 55°F
3,892
Growing degree days, base 60°F
2,771

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January677046
February544258
March41210150
April16551347
May33165597
June2341789
July0471936
August0423888
September5263708
October11777429
November3748151
December585269

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 1.9 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 USC00319100 (Washington Wwtp 4W). Public domain.