Benton County climate

Benton County Frost Dates and Growing Season

NOAA 1991-2020 normals for Prosser, 19.5 km from Benton County, elevation 830 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Prosser. 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 14 and the first fall freeze around October 22, a growing season of about 189 days.

Median at 36°F
last May 2, first October 9
Median at 32°F
last April 14, first October 22
Median at 28°F
last March 23, first November 2

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°FMay 24May 15May 9May 6May 2Apr 30Apr 26Apr 22Apr 16
32°FMay 7May 1Apr 26Apr 19Apr 14Apr 9Apr 4Mar 31Mar 24
28°FApr 22Apr 9Apr 2Mar 28Mar 23Mar 17Mar 12Mar 7Mar 2
24°FMar 31Mar 20Mar 12Mar 7Mar 3Mar 1Feb 26Feb 21Feb 13
20°FMar 12Mar 3Feb 28Feb 25Feb 21Feb 16Feb 10Feb 3Jan 21
16°FFeb 28Feb 23Feb 16Feb 9Feb 3Jan 27Jan 17Jan 7Dec 26

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

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°F183174168163158154148142130
32°F217207200195189184179172161
28°F249242235229224217212202191
24°F279270264259254248243235223
20°F314302293285279273268259250
16°F349334326319311304295285273

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
97% 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
5,172
Cooling degree days, base 65°F
839
Growing degree days, base 40°F
5,503
Growing degree days, base 45°F
4,204
Growing degree days, base 50°F
3,098
Growing degree days, base 55°F
2,179
Growing degree days, base 60°F
1,426

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January97801
February76602
March608027
April3842109
May16844344
June55122518
July7316773
August9271727
September8380449
October3844136
November735012
December99501

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 19.5 km from Benton County. 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 USC00456768 (Prosser). Public domain.