Altamont climate

Altamont Frost Dates and Growing Season

NOAA 1991-2020 normals for Effingham 3SW, 12.4 km from Altamont, elevation 625 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Effingham 3SW. 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 13 and the first fall freeze around October 24, a growing season of about 191 days.

Median at 36°F
last April 24, first October 13
Median at 32°F
last April 13, first October 24
Median at 28°F
last April 2, first November 1

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 11May 5Apr 30Apr 27Apr 24Apr 21Apr 18Apr 14Apr 10
32°FApr 29Apr 23Apr 19Apr 16Apr 13Apr 11Apr 7Apr 5Apr 1
28°FApr 17Apr 11Apr 7Apr 4Apr 2Mar 31Mar 27Mar 22Mar 17
24°FApr 7Apr 2Mar 30Mar 26Mar 22Mar 18Mar 15Mar 11Mar 4
20°FMar 29Mar 22Mar 18Mar 15Mar 12Mar 8Mar 4Feb 28Feb 22
16°FMar 19Mar 14Mar 10Mar 6Mar 3Feb 28Feb 24Feb 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°FSep 29Oct 3Oct 8Oct 11Oct 13Oct 16Oct 19Oct 22Oct 25
32°FOct 9Oct 15Oct 18Oct 22Oct 24Oct 26Oct 28Oct 31Nov 5
28°FOct 20Oct 25Oct 28Oct 31Nov 1Nov 4Nov 8Nov 11Nov 19
24°FNov 1Nov 3Nov 6Nov 10Nov 13Nov 17Nov 21Nov 28Dec 2
20°FNov 8Nov 13Nov 17Nov 21Nov 25Nov 30Dec 3Dec 7Dec 14
16°FNov 15Nov 23Nov 28Dec 1Dec 5Dec 10Dec 15Dec 19Dec 24

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°F190184179175170166161156148
32°F211204199195191188183178170
28°F235227222217214209205200194
24°F263254247241235230225220214
20°F283274269264259253248242232
16°F304295290284278273268261252

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
5,126
Cooling degree days, base 65°F
1,298
Growing degree days, base 40°F
6,348
Growing degree days, base 45°F
5,073
Growing degree days, base 50°F
3,936
Growing degree days, base 55°F
2,928
Growing degree days, base 60°F
2,048

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,12403
February898010
March686258
April34216191
May109106466
June10279718
July1380845
August2326789
September56156552
October29631244
November636255
December96707

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 12.4 km from Altamont. 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 USC00112687 (Effingham 3SW). Public domain.