Farmers and gardeners are always interested in the timing of the first frost. Every year we publish some medians dates for the first day with freezing temperatures and the first day with temperatures below 28 degrees. The 32 degree data roughly approximates the date for the first frost and the temperatures of less than or equal to 28 degrees would reflect the first hard freeze. 

 

 

 

One of the things that jumps right off the page is the relatively large difference in the median date for freezing temperatures for some locations. For example, West Liberty has the earliest date of Oct 6^th and nearby NWS Jackson has the latest date, Oct 26^th. When looking at the range of dates, the differences are best explained by the complex terrain and differences in elevation in eastern Kentucky. As the sun starts to set, direct heating continues on the ridge tops and mid slopes, while the valleys begin to cool down, especially those that are oriented from north to south. This causes an inversion to form as the temperatures aloft remain warm.  As this inversion forms, this in essence, disconnects the lowest levels of the atmosphere from above. This then allows the lowest levels to radiate heat out, causing the temperatures to continue to drop in the lowest layers.