Rockcastle County climate

Rockcastle County Frost Dates and Growing Season

NOAA 1991-2020 normals for Mt Vernon, 2.2 km from Rockcastle County, elevation 1160 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 18 and the first fall freeze around October 24, a growing season of about 189 days.

Median at 36°F
last April 30, first October 15
Median at 32°F
last April 18, first October 24
Median at 28°F
last April 2, first November 4

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 16May 10May 6May 3Apr 30Apr 26Apr 22Apr 18Apr 14
32°FMay 6Apr 30Apr 25Apr 21Apr 18Apr 14Apr 10Apr 5Mar 31
28°FApr 21Apr 14Apr 9Apr 6Apr 2Mar 31Mar 28Mar 23Mar 18
24°FApr 7Apr 2Mar 30Mar 26Mar 22Mar 19Mar 15Mar 10Mar 2
20°FMar 29Mar 22Mar 18Mar 14Mar 10Mar 6Mar 2Feb 26Feb 19
16°FMar 18Mar 13Mar 8Mar 3Feb 28Feb 24Feb 18Feb 11Feb 3

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 3Oct 7Oct 10Oct 13Oct 15Oct 18Oct 21Oct 23Oct 27
32°FOct 13Oct 17Oct 20Oct 22Oct 24Oct 27Oct 29Nov 1Nov 5
28°FOct 22Oct 27Oct 30Nov 1Nov 4Nov 6Nov 9Nov 12Nov 18
24°FNov 2Nov 5Nov 8Nov 12Nov 15Nov 19Nov 23Nov 29Dec 4
20°FNov 8Nov 13Nov 18Nov 23Nov 27Dec 1Dec 4Dec 9Dec 19
16°FNov 18Nov 27Dec 1Dec 6Dec 11Dec 18Dec 24Dec 29Jan 5

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°F187180176172169164160155149
32°F211204198194189185180175167
28°F237229223218213209204198190
24°F262255248243238233228222214
20°F291282274268261256249243234
16°F318307300294287281274267256

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
4,600
Cooling degree days, base 65°F
1,100
Growing degree days, base 40°F
6,399
Growing degree days, base 45°F
5,048
Growing degree days, base 50°F
3,839
Growing degree days, base 55°F
2,778
Growing degree days, base 60°F
1,864

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January980013
February786019
March621479
April31325225
May11688442
June14216652
July1317781
August3283745
September52140539
October28324246
November585271
December848025

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 2.2 km from Rockcastle 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 USC00155648 (Mt Vernon). Public domain.