Linn County climate

Linn County Frost Dates and Growing Season

NOAA 1991-2020 normals for Chillicothe 22 Ene, 3.4 km from Linn County, elevation 833 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Chillicothe 22 Ene. 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 15 and the first fall freeze around October 20, a growing season of about 184 days.

Median at 36°F
last April 28, first October 9
Median at 32°F
last April 15, first October 20
Median at 28°F
last April 5, first October 29

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 13May 7May 4May 1Apr 28Apr 24Apr 21Apr 16Apr 11
32°FMay 2Apr 27Apr 23Apr 19Apr 15Apr 12Apr 8Apr 5Apr 1
28°FApr 20Apr 14Apr 10Apr 7Apr 5Apr 2Mar 31Mar 26Mar 20
24°FApr 10Apr 4Apr 1Mar 29Mar 25Mar 22Mar 18Mar 13Mar 8
20°FMar 31Mar 26Mar 22Mar 18Mar 15Mar 11Mar 9Mar 5Mar 1
16°FMar 23Mar 17Mar 13Mar 10Mar 7Mar 4Mar 1Feb 27Feb 19

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 25Sep 29Oct 3Oct 6Oct 9Oct 11Oct 14Oct 18Oct 22
32°FOct 5Oct 11Oct 15Oct 18Oct 20Oct 23Oct 25Oct 28Nov 1
28°FOct 16Oct 21Oct 24Oct 27Oct 29Nov 1Nov 3Nov 7Nov 12
24°FOct 26Oct 30Nov 2Nov 5Nov 7Nov 11Nov 14Nov 19Nov 27
20°FNov 2Nov 7Nov 10Nov 15Nov 19Nov 23Nov 27Dec 1Dec 6
16°FNov 9Nov 16Nov 20Nov 24Nov 29Dec 1Dec 5Dec 10Dec 18

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°F183176172167162158154149141
32°F205199194189184181176170161
28°F228222216211207203199194188
24°F251243236232227223219214207
20°F272262256250246241237231223
16°F291282276269263259254249241

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
5,562
Cooling degree days, base 65°F
1,053
Growing degree days, base 40°F
5,880
Growing degree days, base 45°F
4,647
Growing degree days, base 50°F
3,545
Growing degree days, base 55°F
2,580
Growing degree days, base 60°F
1,748

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,19601
February94809
March700254
April37210165
May14468396
June10219660
July3325787
August4284745
September82122492
October35321197
November697135
December1,05503

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 3.4 km from Linn 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 USW00013301 (Chillicothe 22 Ene). Public domain.