Altha climate

Altha Frost Dates and Growing Season

NOAA 1991-2020 normals for Marianna Muni AP, 29.9 km from Altha, elevation 113 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Marianna Muni 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 1 and the first fall freeze around November 27, a growing season of about 270 days.

Median at 36°F
last March 16, first November 13
Median at 32°F
last March 1, first November 27
Median at 28°F
last February 9, first December 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 5Mar 30Mar 24Mar 20Mar 16Mar 12Mar 8Mar 2Feb 23
32°FMar 21Mar 15Mar 10Mar 5Mar 1Feb 25Feb 18Feb 11Feb 2
28°FMar 10Feb 28Feb 23Feb 16Feb 9Feb 3Jan 28Jan 19Jan 7
24°FFeb 27Feb 15Feb 6Feb 1Jan 28Jan 21Jan 14Jan 5Dec 28
20°FFeb 8Feb 2Jan 30Jan 25Jan 20Jan 15Jan 9Jan 4Dec 26
16°F–––––––––

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 30Nov 3Nov 6Nov 10Nov 13Nov 16Nov 20Nov 24Dec 1
32°FNov 8Nov 14Nov 18Nov 23Nov 27Dec 1Dec 5Dec 12Dec 28
28°FNov 19Nov 29Dec 4Dec 11Dec 22Dec 29Jan 3Jan 8Jan 21
24°FDec 4Dec 14Dec 27Jan 1Jan 5Jan 10Jan 17Jan 26Feb 5
20°FDec 11Dec 28Jan 3Jan 9Jan 12Jan 17Jan 23Jan 30Feb 6
16°F–––––––––

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°F268260253247242237232226217
32°F305294285278270264258250243
28°F345335324315308300291281270
24°F365365363350340334328316305
20°F365365365365365365362347333
16°F365365365365365365365365365

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
97% of years
24°F or colder
73% of years
20°F or colder
34% of years
16°F or colder
7% 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
1,522
Cooling degree days, base 65°F
2,755
Growing degree days, base 40°F
10,381
Growing degree days, base 45°F
8,615
Growing degree days, base 50°F
6,933
Growing degree days, base 55°F
5,384
Growing degree days, base 60°F
3,983

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January42011153
February28517192
March16150364
April49127529
May3339801
June0484934
July05491,014
August0530995
September1410859
October41183606
November20138301
December36317184

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 29.9 km from Altha. 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 USW00003818 (Marianna Muni AP). Public domain.