Washington climate

Washington Frost Dates and Growing Season

NOAA 1991-2020 normals for St George, 8.9 km from Washington, elevation 2857 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for St George. 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 14 and the first fall freeze around November 10, a growing season of about 239 days.

Median at 36°F
last April 3, first November 1
Median at 32°F
last March 14, first November 10
Median at 28°F
last February 27, first November 20

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 21Apr 15Apr 11Apr 8Apr 3Mar 31Mar 27Mar 22Mar 17
32°FApr 6Mar 31Mar 25Mar 19Mar 14Mar 11Mar 8Mar 4Feb 27
28°FMar 17Mar 10Mar 5Mar 1Feb 27Feb 24Feb 20Feb 15Feb 7
24°FFeb 28Feb 22Feb 18Feb 13Feb 9Feb 6Feb 2Jan 27Jan 18
20°FFeb 13Feb 6Feb 2Jan 28Jan 21Jan 14Jan 6Jan 1Dec 22
16°FJan 28Jan 20Jan 11Jan 5Jan 2Dec 31Dec 24Dec 20Dec 11

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 19Oct 24Oct 27Oct 30Nov 1Nov 4Nov 6Nov 9Nov 12
32°FOct 27Nov 1Nov 5Nov 8Nov 10Nov 12Nov 15Nov 18Nov 22
28°FNov 7Nov 13Nov 15Nov 18Nov 20Nov 22Nov 25Nov 29Dec 3
24°FNov 18Nov 22Nov 24Nov 28Dec 1Dec 4Dec 8Dec 12Dec 18
20°FNov 27Dec 4Dec 8Dec 11Dec 16Dec 20Dec 27Jan 1Jan 13
16°FDec 5Dec 11Dec 16Dec 21Dec 25Dec 30Jan 1Jan 6Jan 18

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°F229223218213208204199194186
32°F260253248243239234228220212
28°F290281275270266262257252243
24°F322312304299294289285279272
20°F361350343337331326317309299
16°F365365365365364358353345335

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
93% of years
16°F or colder
47% 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
3,205
Cooling degree days, base 65°F
2,416
Growing degree days, base 40°F
8,469
Growing degree days, base 45°F
6,910
Growing degree days, base 50°F
5,546
Growing degree days, base 55°F
4,355
Growing degree days, base 60°F
3,310

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January73802
February536024
March3622146
April17031317
May38207634
June2466913
July06761,141
August06231,088
September5351796
October12161410
November473073
December76102

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 8.9 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 USC00427516 (St George). Public domain.