Kittitas County climate

Kittitas County Frost Dates and Growing Season

NOAA 1991-2020 normals for Ellensburg Bowers Fld, 15.1 km from Kittitas County, elevation 1766 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ellensburg Bowers Fld. 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 7, a growing season of about 163 days.

Median at 36°F
last May 11, first September 26
Median at 32°F
last April 28, first October 7
Median at 28°F
last April 11, first October 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°FJun 5May 26May 18May 14May 11May 7May 4May 1Apr 28
32°FMay 12May 7May 3Apr 30Apr 28Apr 25Apr 22Apr 18Apr 13
28°FApr 30Apr 24Apr 19Apr 15Apr 11Apr 8Apr 4Mar 31Mar 24
24°FApr 13Apr 6Apr 1Mar 27Mar 23Mar 18Mar 14Mar 10Mar 2
20°FMar 24Mar 15Mar 10Mar 5Mar 1Feb 26Feb 22Feb 15Feb 5
16°FMar 7Mar 1Feb 25Feb 19Feb 13Feb 6Jan 31Jan 22Jan 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°FSep 12Sep 17Sep 21Sep 24Sep 26Sep 29Oct 1Oct 3Oct 7
32°FSep 26Oct 1Oct 3Oct 5Oct 7Oct 10Oct 14Oct 17Oct 22
28°FOct 7Oct 11Oct 14Oct 17Oct 20Oct 23Oct 26Oct 30Nov 3
24°FOct 17Oct 22Oct 25Oct 29Nov 1Nov 4Nov 7Nov 12Nov 18
20°FOct 27Nov 1Nov 6Nov 11Nov 15Nov 19Nov 24Nov 28Dec 4
16°FNov 5Nov 12Nov 19Nov 25Nov 29Dec 3Dec 8Dec 17Dec 30

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°F155149143139135131126119109
32°F185176172167163159155150143
28°F214207201196191187182176169
24°F250241234227221216211205196
20°F294281270264258252245237226
16°F331319308301293284276266255

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
99% 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
5,970
Cooling degree days, base 65°F
568
Growing degree days, base 40°F
4,685
Growing degree days, base 45°F
3,515
Growing degree days, base 50°F
2,532
Growing degree days, base 55°F
1,718
Growing degree days, base 60°F
1,059

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,07400
February82601
March71008
April482061
May23920260
June9570425
July17222669
August16207657
September13147369
October478181
November82003
December1,08200

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 15.1 km from Kittitas County. 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 USW00024220 (Ellensburg Bowers Fld). Public domain.