Kittitas climate

Kittitas Frost Dates and Growing Season

NOAA 1991-2020 normals for Ellensburg, 9.5 km from Kittitas, elevation 1480 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ellensburg. 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 May 8 and the first fall freeze around October 2, a growing season of about 146 days.

Median at 36°F
last May 23, first September 21
Median at 32°F
last May 8, first October 2
Median at 28°F
last April 23, first October 14

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 16Jun 7Jun 1May 27May 23May 20May 16May 13May 8
32°FMay 25May 18May 14May 11May 8May 6May 2Apr 30Apr 25
28°FMay 6May 2Apr 30Apr 26Apr 23Apr 20Apr 18Apr 14Apr 9
24°FApr 21Apr 15Apr 11Apr 8Apr 5Apr 1Mar 29Mar 25Mar 14
20°FApr 5Mar 30Mar 24Mar 18Mar 13Mar 9Mar 5Mar 1Feb 25
16°FMar 16Mar 9Mar 4Mar 1Feb 26Feb 23Feb 17Feb 11Feb 1

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 8Sep 12Sep 16Sep 18Sep 21Sep 23Sep 26Sep 29Oct 2
32°FSep 20Sep 24Sep 27Sep 30Oct 2Oct 4Oct 6Oct 10Oct 14
28°FOct 1Oct 5Oct 8Oct 11Oct 14Oct 16Oct 19Oct 23Oct 28
24°FOct 9Oct 15Oct 19Oct 23Oct 26Oct 29Nov 1Nov 4Nov 10
20°FOct 23Oct 29Nov 1Nov 4Nov 8Nov 12Nov 16Nov 21Nov 28
16°FNov 1Nov 9Nov 14Nov 19Nov 23Nov 26Dec 1Dec 5Dec 13

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°F14013212712311811310710294
32°F165159154151146143139134125
28°F194186181177173169165161154
24°F229220214210204199194188182
20°F266257250244239233228221211
16°F302291284277271266259250241

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
6,671
Cooling degree days, base 65°F
390
Growing degree days, base 40°F
4,090
Growing degree days, base 45°F
3,009
Growing degree days, base 50°F
2,113
Growing degree days, base 55°F
1,374
Growing degree days, base 60°F
796

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,15900
February91000
March78003
April543041
May30011201
June14148358
July36166595
August39138565
September18427299
October543050
November87901
December1,15800

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 9.5 km from Kittitas. 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 USC00452505 (Ellensburg). Public domain.