Altamont climate

Altamont Frost Dates and Growing Season

NOAA 1991-2020 normals for Coalmont, 7.1 km from Altamont, elevation 1856 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Coalmont. 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 21 and the first fall freeze around October 20, a growing season of about 182 days.

Median at 36°F
last May 2, first October 11
Median at 32°F
last April 21, first October 20
Median at 28°F
last April 7, first October 30

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 19May 13May 9May 6May 2Apr 30Apr 26Apr 22Apr 16
32°FMay 10May 3Apr 30Apr 25Apr 21Apr 17Apr 13Apr 8Apr 1
28°FApr 29Apr 20Apr 14Apr 10Apr 7Apr 3Mar 31Mar 26Mar 20
24°FApr 11Apr 5Apr 1Mar 28Mar 25Mar 21Mar 17Mar 11Mar 5
20°FMar 30Mar 25Mar 21Mar 17Mar 11Mar 7Mar 2Feb 27Feb 18
16°FMar 22Mar 15Mar 8Mar 3Feb 27Feb 22Feb 14Feb 7Jan 31

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 8Oct 11Oct 14Oct 17Oct 20Oct 24
32°FOct 7Oct 11Oct 15Oct 18Oct 20Oct 23Oct 25Oct 29Nov 2
28°FOct 16Oct 20Oct 24Oct 27Oct 30Nov 1Nov 4Nov 9Nov 15
24°FOct 26Nov 1Nov 3Nov 6Nov 10Nov 13Nov 18Nov 24Dec 1
20°FNov 6Nov 11Nov 15Nov 20Nov 24Nov 29Dec 2Dec 6Dec 15
16°FNov 16Nov 23Nov 29Dec 2Dec 6Dec 11Dec 19Dec 27Jan 6

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°F181175170165161157152148141
32°F204197191186182177172166159
28°F232223216210206201197190181
24°F258249242237231226221215206
20°F289278270264259254247241233
16°F322309302294287279272264255

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
4,477
Cooling degree days, base 65°F
818
Growing degree days, base 40°F
6,092
Growing degree days, base 45°F
4,708
Growing degree days, base 50°F
3,486
Growing degree days, base 55°F
2,435
Growing degree days, base 60°F
1,544

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January916015
February745017
March591167
April3268188
May12349397
June14160595
July2256719
August4227688
September57105499
October29813223
November577157
December825021

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 7.1 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 USC00401887 (Coalmont). Public domain.