Marion County climate

Marion County Frost Dates and Growing Season

NOAA 1991-2020 normals for Hamilton 3 S, 10.6 km from Marion County, elevation 435 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Hamilton 3 S. 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 11 and the first fall freeze around October 27, a growing season of about 198 days.

Median at 36°F
last April 23, first October 19
Median at 32°F
last April 11, first October 27
Median at 28°F
last March 31, first November 4

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 7May 2Apr 30Apr 26Apr 23Apr 20Apr 16Apr 12Apr 7
32°FApr 27Apr 22Apr 18Apr 14Apr 11Apr 8Apr 5Mar 31Mar 26
28°FApr 16Apr 10Apr 6Apr 3Mar 31Mar 27Mar 23Mar 18Mar 11
24°FApr 4Mar 30Mar 25Mar 20Mar 16Mar 11Mar 6Mar 1Feb 24
20°FMar 21Mar 15Mar 10Mar 5Mar 1Feb 26Feb 21Feb 14Feb 5
16°FMar 11Mar 4Feb 27Feb 20Feb 13Feb 7Feb 2Jan 28Jan 17

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 7Oct 11Oct 14Oct 17Oct 19Oct 22Oct 24Oct 27Oct 31
32°FOct 15Oct 19Oct 22Oct 25Oct 27Oct 30Nov 1Nov 3Nov 10
28°FOct 22Oct 28Oct 31Nov 1Nov 4Nov 7Nov 13Nov 18Nov 25
24°FNov 1Nov 4Nov 8Nov 13Nov 17Nov 21Nov 26Dec 1Dec 7
20°FNov 9Nov 17Nov 23Nov 28Dec 2Dec 7Dec 13Dec 24Jan 1
16°FNov 22Dec 1Dec 8Dec 15Dec 23Dec 30Jan 3Jan 11Jan 25

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°F199192187183179175171167160
32°F220213207203198194190185178
28°F247240233227222217212207199
24°F278268261255248243236229220
20°F311300291285278271264256249
16°F343332323315308303296287272

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
3,303
Cooling degree days, base 65°F
1,781
Growing degree days, base 40°F
7,907
Growing degree days, base 45°F
6,381
Growing degree days, base 50°F
5,001
Growing degree days, base 55°F
3,770
Growing degree days, base 60°F
2,697

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January764138
February580253
March41010158
April18942320
May47155574
June1340789
July0459924
August0437902
September14263699
October16964374
November4547118
December676253

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 10.6 km from Marion 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 USC00013645 (Hamilton 3 S). Public domain.