Osborne County climate

Osborne County Frost Dates and Growing Season

NOAA 1991-2020 normals for Alton 1 W, 22.4 km from Osborne County, elevation 1685 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Alton 1 W. 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 29 and the first fall freeze around October 12, a growing season of about 164 days.

Median at 36°F
last May 7, first October 2
Median at 32°F
last April 29, first October 12
Median at 28°F
last April 19, first October 22

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 22May 15May 12May 9May 7May 4May 2Apr 30Apr 25
32°FMay 11May 6May 4May 1Apr 29Apr 26Apr 23Apr 19Apr 16
28°FMay 3Apr 30Apr 26Apr 22Apr 19Apr 16Apr 14Apr 10Apr 5
24°FApr 25Apr 20Apr 15Apr 12Apr 8Apr 5Apr 3Mar 31Mar 25
20°FApr 17Apr 9Apr 5Apr 2Mar 31Mar 27Mar 22Mar 17Mar 10
16°FApr 5Mar 31Mar 26Mar 20Mar 16Mar 12Mar 8Mar 4Feb 28

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 21Sep 24Sep 27Sep 30Oct 2Oct 5Oct 8Oct 12Oct 16
32°FSep 28Oct 2Oct 5Oct 8Oct 12Oct 15Oct 18Oct 22Oct 27
28°FOct 7Oct 12Oct 17Oct 19Oct 22Oct 25Oct 28Nov 1Nov 4
24°FOct 17Oct 20Oct 24Oct 28Oct 31Nov 2Nov 4Nov 7Nov 11
20°FOct 23Oct 30Nov 1Nov 4Nov 7Nov 10Nov 13Nov 17Nov 21
16°FOct 31Nov 4Nov 9Nov 12Nov 16Nov 20Nov 23Nov 27Dec 1

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°F166159154150147144140136129
32°F182176172168164161157151145
28°F203196191186182178174169164
24°F222216209205201197193187181
20°F246237231226222216211206198
16°F268260253248244239233225214

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
5,584
Cooling degree days, base 65°F
1,334
Growing degree days, base 40°F
6,098
Growing degree days, base 45°F
4,881
Growing degree days, base 50°F
3,801
Growing degree days, base 55°F
2,852
Growing degree days, base 60°F
2,027

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,14700
February92506
March717047
April41610143
May15672390
June18274706
July1433897
August4363824
September70157540
October34524215
November725133
December1,06101

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 22.4 km from Osborne 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 USC00140201 (Alton 1 W). Public domain.