Posey County climate

Posey County Frost Dates and Growing Season

NOAA 1991-2020 normals for Mt Vernon, 10.7 km from Posey County, elevation 357 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Mt Vernon. 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 7 and the first fall freeze around October 28, a growing season of about 202 days.

Median at 36°F
last April 21, first October 17
Median at 32°F
last April 7, first October 28
Median at 28°F
last March 30, first November 7

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 7May 2Apr 28Apr 24Apr 21Apr 17Apr 14Apr 10Apr 5
32°FApr 27Apr 20Apr 15Apr 11Apr 7Apr 5Apr 2Mar 31Mar 25
28°FApr 14Apr 7Apr 4Apr 1Mar 30Mar 26Mar 22Mar 17Mar 12
24°FApr 2Mar 29Mar 25Mar 21Mar 17Mar 14Mar 11Mar 6Feb 28
20°FMar 22Mar 17Mar 13Mar 10Mar 6Mar 3Feb 27Feb 22Feb 13
16°FMar 15Mar 8Mar 4Feb 28Feb 24Feb 19Feb 14Feb 8Feb 1

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°FOct 1Oct 7Oct 12Oct 14Oct 17Oct 20Oct 23Oct 26Oct 30
32°FOct 10Oct 16Oct 21Oct 25Oct 28Oct 30Nov 1Nov 5Nov 10
28°FOct 24Oct 31Nov 2Nov 5Nov 7Nov 11Nov 14Nov 19Nov 25
24°FNov 5Nov 9Nov 13Nov 17Nov 20Nov 24Nov 28Dec 2Dec 7
20°FNov 12Nov 19Nov 24Nov 28Dec 1Dec 5Dec 10Dec 15Dec 22
16°FNov 22Nov 28Dec 2Dec 7Dec 11Dec 17Dec 22Dec 27Jan 4

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°F199192187182177174169164157
32°F222215210206202196191185177
28°F247240234229224219214209200
24°F274266258253248243238232224
20°F297288282277272267261254246
16°F319308302296291286280273264

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
4,609
Cooling degree days, base 65°F
1,341
Growing degree days, base 40°F
6,625
Growing degree days, base 45°F
5,288
Growing degree days, base 50°F
4,094
Growing degree days, base 55°F
3,037
Growing degree days, base 60°F
2,119

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,01506
February816010
March633264
April30017216
May89106484
June7288730
July0380845
August1342806
September41174584
October25433272
November573268
December880010

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 10.7 km from Posey 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 USC00126001 (Mt Vernon). Public domain.