Marietta climate

Marietta Frost Dates and Growing Season

NOAA 1991-2020 normals for Marietta Wwtp, 2 km from Marietta, elevation 610 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Marietta Wwtp. 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 18 and the first fall freeze around October 27, a growing season of about 191 days.

Median at 36°F
last April 30, first October 16
Median at 32°F
last April 18, first October 27
Median at 28°F
last April 5, first November 5

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 17May 10May 6May 3Apr 30Apr 27Apr 23Apr 20Apr 16
32°FMay 4Apr 29Apr 24Apr 21Apr 18Apr 16Apr 13Apr 9Apr 5
28°FApr 19Apr 14Apr 11Apr 7Apr 5Apr 2Mar 31Mar 27Mar 22
24°FApr 6Apr 2Mar 30Mar 27Mar 24Mar 21Mar 18Mar 15Mar 8
20°FMar 28Mar 23Mar 19Mar 17Mar 14Mar 11Mar 7Mar 2Feb 24
16°FMar 19Mar 14Mar 10Mar 6Mar 3Feb 28Feb 22Feb 16Feb 9

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 7Oct 10Oct 14Oct 16Oct 18Oct 21Oct 24Oct 29
32°FOct 13Oct 17Oct 20Oct 24Oct 27Oct 30Nov 1Nov 3Nov 6
28°FOct 24Oct 29Nov 1Nov 2Nov 5Nov 8Nov 11Nov 14Nov 19
24°FNov 2Nov 6Nov 9Nov 12Nov 15Nov 18Nov 22Nov 27Dec 4
20°FNov 11Nov 17Nov 21Nov 26Nov 30Dec 4Dec 9Dec 16Dec 24
16°FNov 22Nov 30Dec 6Dec 11Dec 17Dec 23Dec 27Jan 1Jan 8

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°F188181176173169164160155148
32°F210203199195191186181177171
28°F235228222218214211206201194
24°F262254248242237233228223216
20°F290281273267262257252246239
16°F317307302295289283277270260

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
5,076
Cooling degree days, base 65°F
1,038
Growing degree days, base 40°F
5,998
Growing degree days, base 45°F
4,719
Growing degree days, base 50°F
3,587
Growing degree days, base 55°F
2,597
Growing degree days, base 60°F
1,747

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,05106
February88107
March719143
April36410169
May13276414
June16206640
July1320784
August2281744
September55127523
October32016203
November633044
December904011

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 km from Marietta. 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 USC00334927 (Marietta Wwtp). Public domain.