Marietta climate

Marietta Frost Dates and Growing Season

NOAA 1991-2020 normals for Bellingham Intl AP, 3.2 km from Marietta, elevation 149 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Bellingham Intl AP. 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 31 and the first fall freeze around October 30, a growing season of about 211 days.

Median at 36°F
last April 25, first October 13
Median at 32°F
last March 31, first October 30
Median at 28°F
last March 4, first November 16

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 12May 6May 2Apr 29Apr 25Apr 22Apr 17Apr 13Apr 7
32°FApr 18Apr 12Apr 6Apr 2Mar 31Mar 26Mar 21Mar 17Mar 10
28°FMar 25Mar 18Mar 14Mar 9Mar 4Feb 28Feb 26Feb 20Feb 9
24°FMar 4Feb 28Feb 24Feb 18Feb 10Feb 1Jan 25Jan 14Jan 3
20°FFeb 18Feb 3Jan 28Jan 20Jan 13Jan 6Jan 1Dec 21Dec 7
16°FFeb 2Jan 26Jan 18Jan 11Jan 4Dec 31Dec 19Dec 9Dec 2

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

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°F196187181177172167162156150
32°F240231224217211206201194187
28°F290277269262255249243237229
24°F345328319310303294286276266
20°F365365359350342334328317304
16°F365365365365365364351340330

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
98% of years
20°F or colder
75% of years
16°F or colder
40% 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
5,110
Cooling degree days, base 65°F
75
Growing degree days, base 40°F
4,344
Growing degree days, base 45°F
2,905
Growing degree days, base 50°F
1,765
Growing degree days, base 55°F
924
Growing degree days, base 60°F
352

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January77005
February65204
March615011
April461046
May2971176
June1648294
July6731429
August6531431
September1894266
October433082
November617017
December78104

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 Marietta. 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 USW00024217 (Bellingham Intl AP). Public domain.