Tri-Cities climate

Tri-Cities Frost Dates and Growing Season

NOAA 1991-2020 normals for Pasco Tri Cities AP, 6.6 km from Tri-Cities, elevation 407 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Pasco Tri Cities AP. 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 27 and the first fall freeze around October 11, a growing season of about 168 days.

Median at 36°F
last May 9, first September 29
Median at 32°F
last April 27, first October 11
Median at 28°F
last April 7, first October 23

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 23May 18May 14May 11May 9May 7May 4May 1Apr 27
32°FMay 10May 6May 2Apr 29Apr 27Apr 23Apr 19Apr 14Apr 8
28°FApr 28Apr 21Apr 15Apr 11Apr 7Apr 2Mar 30Mar 27Mar 20
24°FApr 6Mar 31Mar 28Mar 24Mar 19Mar 14Mar 9Mar 4Feb 27
20°FMar 19Mar 10Mar 5Mar 2Feb 28Feb 24Feb 17Feb 10Feb 1
16°FMar 5Feb 28Feb 24Feb 18Feb 11Feb 3Jan 23Jan 12Dec 31

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 15Sep 20Sep 24Sep 27Sep 29Oct 1Oct 4Oct 7Oct 13
32°FSep 28Oct 1Oct 4Oct 7Oct 11Oct 14Oct 17Oct 21Oct 27
28°FOct 6Oct 11Oct 17Oct 20Oct 23Oct 26Oct 29Nov 1Nov 8
24°FOct 18Oct 23Oct 28Oct 30Nov 2Nov 7Nov 12Nov 18Nov 26
20°FOct 26Nov 1Nov 8Nov 12Nov 18Nov 23Nov 28Dec 5Dec 18
16°FNov 5Nov 14Nov 22Nov 28Dec 4Dec 9Dec 19Dec 29Jan 10

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°F161155150146143139135130124
32°F189182177172168163159155148
28°F224214207202197192187181173
24°F259247240235228223217210202
20°F302290278271263256250242232
16°F339327316306298289280270257

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
98% 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
5,011
Cooling degree days, base 65°F
788
Growing degree days, base 40°F
5,548
Growing degree days, base 45°F
4,228
Growing degree days, base 50°F
3,103
Growing degree days, base 55°F
2,164
Growing degree days, base 60°F
1,392

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January94202
February74503
March594029
April3712116
May15039356
June33118536
July3304765
August5259719
September8663428
October4033128
November723018
December95603

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 6.6 km from Tri-Cities. 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 USW00024163 (Pasco Tri Cities AP). Public domain.