Altamont climate

Altamont Frost Dates and Growing Season

NOAA 1991-2020 normals for Klamath Falls Intl AP, 6.8 km from Altamont, elevation 4084 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Klamath Falls 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 June 9 and the first fall freeze around September 18, a growing season of about 99 days.

Median at 32°F
last June 9, first September 18
Median at 28°F
last May 21, first October 2

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°F–––––––––
32°FJun 26Jun 21Jun 16Jun 12Jun 9Jun 6Jun 3May 30May 22
28°FJun 12Jun 5Jun 1May 26May 21May 16May 13May 8May 2
24°FMay 20May 12May 7May 3May 1Apr 28Apr 24Apr 19Apr 13
20°FMay 1Apr 25Apr 20Apr 16Apr 12Apr 8Apr 4Mar 30Mar 21
16°FApr 11Apr 3Mar 27Mar 20Mar 14Mar 8Mar 2Feb 25Feb 15

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°F–––––––––
32°FSep 4Sep 9Sep 13Sep 16Sep 18Sep 20Sep 23Sep 27Oct 1
28°FSep 17Sep 23Sep 26Sep 29Oct 2Oct 5Oct 7Oct 12Oct 17
24°FOct 2Oct 6Oct 10Oct 14Oct 17Oct 20Oct 23Oct 26Nov 1
20°FOct 14Oct 20Oct 23Oct 26Oct 30Nov 2Nov 5Nov 10Nov 17
16°FOct 26Nov 1Nov 5Nov 10Nov 13Nov 18Nov 22Nov 28Dec 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°F918580767268635645
32°F1201141081049995918677
28°F158149143138132127121115106
24°F191183178173168163158151143
20°F229219212207202196190183174
16°F279264256248241234227220209

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
6,710
Cooling degree days, base 65°F
217
Growing degree days, base 40°F
3,645
Growing degree days, base 45°F
2,591
Growing degree days, base 50°F
1,747
Growing degree days, base 55°F
1,080
Growing degree days, base 60°F
562

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,03900
February84300
March79402
April647019
May4153122
June20721276
July41104529
August5474486
September21614262
October544050
November84003
December1,07100

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 6.8 km from Altamont. 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 USW00094236 (Klamath Falls Intl AP). Public domain.