Altona climate

Altona Frost Dates and Growing Season

NOAA 1991-2020 normals for Ellenburg Depot, 13.4 km from Altona, elevation 950 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Ellenburg Depot. 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 May 10 and the first fall freeze around October 2, a growing season of about 144 days.

Median at 36°F
last May 24, first September 22
Median at 32°F
last May 10, first October 2
Median at 28°F
last April 29, first October 14

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°FJun 6Jun 2May 31May 27May 24May 21May 18May 13May 8
32°FMay 25May 21May 17May 13May 10May 7May 3Apr 30Apr 27
28°FMay 13May 7May 4May 1Apr 29Apr 26Apr 24Apr 21Apr 15
24°FApr 30Apr 25Apr 22Apr 19Apr 16Apr 13Apr 11Apr 8Apr 5
20°FApr 19Apr 14Apr 11Apr 8Apr 6Apr 4Apr 2Mar 31Mar 25
16°FApr 11Apr 7Apr 4Apr 3Apr 1Mar 30Mar 26Mar 22Mar 18

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 9Sep 13Sep 16Sep 19Sep 22Sep 24Sep 26Sep 29Oct 3
32°FSep 17Sep 23Sep 26Sep 30Oct 2Oct 5Oct 7Oct 11Oct 18
28°FSep 30Oct 4Oct 7Oct 10Oct 14Oct 18Oct 22Oct 28Nov 2
24°FOct 10Oct 18Oct 23Oct 26Oct 30Nov 1Nov 4Nov 7Nov 12
20°FOct 27Nov 1Nov 3Nov 5Nov 9Nov 11Nov 15Nov 18Nov 23
16°FNov 4Nov 8Nov 12Nov 15Nov 18Nov 20Nov 23Nov 27Dec 2

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°F139132128124120116111106100
32°F165158153149144140135130124
28°F189183178172168164159153146
24°F212206202198194190185180173
20°F233227223219215211208204197
16°F250244239235231228223219213

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
8,159
Cooling degree days, base 65°F
334
Growing degree days, base 40°F
3,875
Growing degree days, base 45°F
2,897
Growing degree days, base 50°F
2,052
Growing degree days, base 55°F
1,331
Growing degree days, base 60°F
744

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,50600
February1,30000
March1,14619
April710124
May34115191
June10760405
July30134569
August5187501
September22536280
October567163
November890011
December1,28600

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 13.4 km from Altona. 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 USC00302574 (Ellenburg Depot). Public domain.