Union County climate

Union County Frost Dates and Growing Season

NOAA 1991-2020 normals for Brookville, 23.7 km from Union County, elevation 630 ft

Frost and the growing season

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

Median at 36°F
last April 30, first October 10
Median at 32°F
last April 20, first October 21
Median at 28°F
last April 6, first October 31

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 17May 11May 6May 2Apr 30Apr 27Apr 24Apr 21Apr 16
32°FMay 7May 1Apr 26Apr 23Apr 20Apr 17Apr 14Apr 10Apr 6
28°FApr 22Apr 17Apr 13Apr 9Apr 6Apr 4Apr 2Mar 30Mar 23
24°FApr 8Apr 4Apr 1Mar 30Mar 27Mar 24Mar 21Mar 17Mar 11
20°FMar 31Mar 25Mar 21Mar 18Mar 15Mar 12Mar 8Mar 3Feb 26
16°FMar 21Mar 15Mar 11Mar 8Mar 4Mar 1Feb 25Feb 20Feb 11

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 2Oct 5Oct 8Oct 10Oct 12Oct 15Oct 19Oct 23
32°FOct 6Oct 11Oct 15Oct 18Oct 21Oct 23Oct 26Oct 30Nov 3
28°FOct 17Oct 22Oct 26Oct 29Oct 31Nov 2Nov 5Nov 9Nov 15
24°FOct 29Nov 1Nov 5Nov 9Nov 12Nov 15Nov 19Nov 24Dec 1
20°FNov 7Nov 13Nov 18Nov 22Nov 26Dec 1Dec 3Dec 8Dec 17
16°FNov 18Nov 25Nov 30Dec 2Dec 6Dec 11Dec 17Dec 22Dec 27

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°F179173169165162157154149142
32°F202195190186182178173168161
28°F227220215211207203199193186
24°F254246240235230226223217211
20°F281272266260255250244239231
16°F305297290284279274268262253

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
5,245
Cooling degree days, base 65°F
1,092
Growing degree days, base 40°F
6,018
Growing degree days, base 45°F
4,759
Growing degree days, base 50°F
3,639
Growing degree days, base 55°F
2,655
Growing degree days, base 60°F
1,806

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,10704
February91007
March721247
April36812171
May13383422
June16221656
July1323787
August3292755
September62137526
October32021212
November647144
December95909

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 23.7 km from Union County. 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 USC00121030 (Brookville). Public domain.