Marion County climate

Marion County Frost Dates and Growing Season

NOAA 1991-2020 normals for Jefferson, 3.2 km from Marion County, elevation 211 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Jefferson. 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 March 18 and the first fall freeze around November 8, a growing season of about 236 days.

Median at 36°F
last April 2, first October 30
Median at 32°F
last March 18, first November 8
Median at 28°F
last March 3, first November 22

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°FApr 21Apr 14Apr 9Apr 5Apr 2Mar 29Mar 25Mar 20Mar 13
32°FApr 7Apr 1Mar 27Mar 23Mar 18Mar 14Mar 9Mar 5Feb 28
28°FMar 22Mar 15Mar 11Mar 6Mar 3Feb 28Feb 24Feb 18Feb 7
24°FMar 9Mar 2Feb 26Feb 19Feb 14Feb 7Jan 31Jan 25Jan 14
20°FFeb 27Feb 14Feb 5Jan 31Jan 26Jan 20Jan 13Jan 5Dec 26
16°FFeb 11Feb 2Jan 30Jan 23Jan 17Jan 12Jan 6Jan 1Dec 23

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 18Oct 22Oct 25Oct 28Oct 30Nov 1Nov 4Nov 8Nov 15
32°FOct 26Oct 31Nov 2Nov 5Nov 8Nov 12Nov 17Nov 22Nov 30
28°FNov 1Nov 7Nov 12Nov 17Nov 22Nov 28Dec 1Dec 5Dec 12
24°FNov 13Nov 21Nov 28Dec 1Dec 6Dec 12Dec 19Dec 27Jan 5
20°FNov 29Dec 5Dec 13Dec 21Dec 26Jan 1Jan 6Jan 14Jan 30
16°FDec 12Dec 23Dec 29Jan 1Jan 5Jan 9Jan 14Jan 25Feb 3

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°F237228222216212207202197188
32°F263253246241236231225219210
28°F298285277270265259253246237
24°F338326315306299289282274264
20°F365360352345338331322312301
16°F365365365365365364356345334

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
99% of years
20°F or colder
82% of years
16°F or colder
43% 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
2,470
Cooling degree days, base 65°F
2,393
Growing degree days, base 40°F
9,166
Growing degree days, base 45°F
7,515
Growing degree days, base 50°F
6,002
Growing degree days, base 55°F
4,642
Growing degree days, base 60°F
3,435

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January606364
February448496
March28327251
April11183426
May16242691
June0448898
July05611,026
August05471,012
September8343784
October105108473
November33521198
December558582

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 3.2 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 USC00414577 (Jefferson). Public domain.