Ritzville climate

Ritzville Frost Dates and Growing Season

NOAA 1991-2020 normals for Ritzville 1 Sse, 1.3 km from Ritzville, elevation 1864 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ritzville 1 Sse. 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 7 and the first fall freeze around October 10, a growing season of about 153 days.

Median at 36°F
last May 28, first September 28
Median at 32°F
last May 7, first October 10
Median at 28°F
last April 25, first October 21

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 9Jun 4May 31May 28May 24May 18May 14May 8
32°FMay 27May 18May 13May 10May 7May 4May 1Apr 29Apr 25
28°FMay 10May 4May 1Apr 28Apr 25Apr 21Apr 17Apr 11Apr 2
24°FApr 28Apr 20Apr 11Apr 4Mar 30Mar 21Mar 14Mar 8Mar 2
20°FMar 29Mar 15Mar 10Mar 5Mar 1Feb 26Feb 20Feb 11Feb 1
16°FMar 7Mar 1Feb 24Feb 16Feb 8Feb 2Jan 26Jan 14Jan 3

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 10Sep 16Sep 21Sep 24Sep 28Oct 1Oct 4Oct 7Oct 12
32°FSep 27Oct 1Oct 4Oct 6Oct 10Oct 12Oct 15Oct 19Oct 25
28°FOct 4Oct 10Oct 15Oct 18Oct 21Oct 24Oct 27Nov 1Nov 6
24°FOct 16Oct 22Oct 26Oct 30Nov 1Nov 6Nov 9Nov 14Nov 21
20°FOct 25Nov 1Nov 6Nov 11Nov 15Nov 19Nov 24Nov 28Dec 5
16°FNov 6Nov 14Nov 20Nov 25Nov 29Dec 3Dec 9Dec 16Dec 26

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°F14713913312712311711110496
32°F174166161157153149144137127
28°F207197190185179174169164155
24°F253241234226220212203194183
20°F297284275268260253247239229
16°F333319308301292284275265254

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
6,408
Cooling degree days, base 65°F
474
Growing degree days, base 40°F
4,276
Growing degree days, base 45°F
3,166
Growing degree days, base 50°F
2,247
Growing degree days, base 55°F
1,492
Growing degree days, base 60°F
902

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09000
February87200
March76305
April548042
May31612193
June15146347
July32188622
August32177611
September15950347
October499178
November84203
December1,10700

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 1.3 km from Ritzville. 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 USC00457059 (Ritzville 1 Sse). Public domain.