Marion County climate

Marion County Frost Dates and Growing Season

NOAA 1991-2020 normals for Salem, 2.6 km from Marion County, elevation 550 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Salem. 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 9 and the first fall freeze around October 26, a growing season of about 197 days.

Median at 36°F
last April 21, first October 17
Median at 32°F
last April 9, first October 26
Median at 28°F
last March 30, first November 3

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 6May 1Apr 27Apr 23Apr 21Apr 18Apr 15Apr 11Apr 7
32°FApr 23Apr 18Apr 14Apr 11Apr 9Apr 5Apr 3Mar 31Mar 25
28°FApr 14Apr 9Apr 4Apr 1Mar 30Mar 28Mar 24Mar 20Mar 14
24°FApr 4Mar 30Mar 26Mar 23Mar 19Mar 16Mar 13Mar 9Mar 4
20°FMar 24Mar 19Mar 16Mar 13Mar 9Mar 6Mar 3Feb 28Feb 21
16°FMar 17Mar 13Mar 9Mar 6Mar 2Feb 28Feb 23Feb 16Feb 8

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°FOct 3Oct 8Oct 11Oct 14Oct 17Oct 19Oct 22Oct 24Oct 28
32°FOct 13Oct 18Oct 21Oct 24Oct 26Oct 29Oct 31Nov 2Nov 6
28°FOct 23Oct 27Oct 30Nov 1Nov 3Nov 6Nov 10Nov 14Nov 20
24°FNov 1Nov 5Nov 8Nov 12Nov 15Nov 19Nov 23Nov 28Dec 3
20°FNov 9Nov 14Nov 19Nov 24Nov 27Dec 1Dec 4Dec 8Dec 15
16°FNov 17Nov 25Nov 30Dec 3Dec 6Dec 10Dec 15Dec 20Dec 27

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°F196190184180176172168163157
32°F217211205201197194190186179
28°F241232227223219215211205198
24°F264257251245240235230225218
20°F286278272266261256251246238
16°F306299292286280274269263254

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
4,985
Cooling degree days, base 65°F
1,328
Growing degree days, base 40°F
6,450
Growing degree days, base 45°F
5,165
Growing degree days, base 50°F
4,010
Growing degree days, base 55°F
2,986
Growing degree days, base 60°F
2,089

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,09704
February87609
March669361
April32018207
May102107472
June8282724
July0391856
August2339803
September48158560
October28229251
November627256
December95508

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 2.6 km from Marion County. 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 USC00117636 (Salem). Public domain.