Oregon County climate

Oregon County Frost Dates and Growing Season

NOAA 1991-2020 normals for Alton, 0.7 km from Oregon County, elevation 813 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Alton. 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 17 and the first fall freeze around October 21, a growing season of about 187 days.

Median at 36°F
last April 27, first October 11
Median at 32°F
last April 17, first October 21
Median at 28°F
last April 5, 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 11May 5May 2Apr 30Apr 27Apr 24Apr 21Apr 17Apr 12
32°FMay 1Apr 27Apr 23Apr 20Apr 17Apr 13Apr 9Apr 4Mar 30
28°FApr 22Apr 17Apr 12Apr 8Apr 5Apr 1Mar 29Mar 24Mar 17
24°FApr 12Apr 5Apr 1Mar 28Mar 24Mar 20Mar 16Mar 11Mar 6
20°FApr 1Mar 24Mar 19Mar 15Mar 11Mar 8Mar 4Feb 28Feb 22
16°FMar 19Mar 12Mar 8Mar 5Mar 1Feb 27Feb 22Feb 15Feb 6

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 2Oct 5Oct 8Oct 11Oct 13Oct 16Oct 20Oct 24
32°FOct 7Oct 12Oct 16Oct 19Oct 21Oct 23Oct 26Oct 30Nov 3
28°FOct 16Oct 20Oct 25Oct 27Oct 30Nov 1Nov 4Nov 7Nov 14
24°FOct 25Oct 30Nov 2Nov 5Nov 8Nov 12Nov 16Nov 22Nov 28
20°FNov 4Nov 8Nov 13Nov 17Nov 21Nov 26Dec 1Dec 4Dec 10
16°FNov 12Nov 19Nov 25Nov 30Dec 3Dec 8Dec 13Dec 21Dec 30

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°F187179174170166162158154147
32°F210202197192187182177172166
28°F233225218213208204199193185
24°F256247240235230225220213204
20°F281271265259253248242233224
16°F307297291284278273267259249

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
4,622
Cooling degree days, base 65°F
1,261
Growing degree days, base 40°F
6,514
Growing degree days, base 45°F
5,176
Growing degree days, base 50°F
3,981
Growing degree days, base 55°F
2,930
Growing degree days, base 60°F
2,022

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January989012
February788014
March592379
April29524225
May10386449
June8258700
July1376840
August2348810
September50143544
October28622239
November603156
December905012

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 0.7 km from Oregon County. 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 USC00230127 (Alton). Public domain.