If you live in eastern Kentucky, and it seems that it does not get as cold as it used to in the winter, it is not your imagination. Major cold air outbreaks in eastern Kentucky have become increasingly rare over the past couple of decades.
So far this winter the the lowest minimum temperature recorded at the National Weather Service Weather Forecast Office (WFO) in Jackson has been 17 degrees, while the lowest minimum temperature recorded at London, Kentucky has been 16 degrees. Climate records at Jackson date back to January 1981, while climate records at London date back to November 1954.
The warmest minimum temperature ever recorded for an entire winter season at Jackson was11 degrees in the winter of 1997-1998. For London the warmest minimum temperature ever recorded for an entire winter season was 10 degrees in the winter of 2001-2002.
The following graphs illustrate the lack of major cold air outbreaks in eastern Kentukcy over the past couple of decades. The first graph (Figure 1) shows the coldest minimum temperature recorded at Jackson for each winter from 1981 to 2012 (through Febraury 6). Temperatures fell below zero in 8 of 16 winters from 1980-81 to 1995-96, but fell below zero in only one of 16 winters since.
The second graph (Figure 2) is even more revealing, since it shows data all the way back to the winter of 1954-55 for London, Kentucky. This graph shows the coldest minimum temperature recorded at London for each winter from 1954-55 to 2011-2012 (through Febraury 6). At London, temperatures fell below zero in 30 of 42 winters from 1954-55 through 1995-95, but have fallen below zero in only one of 16 winters since.
From the winter of 1954-55 through the winter of 1995-96 the average coldest temperature recoded at London during each winter was -6 degrees Fahrenheit. Since 1996 the average coldest temperature recorded at London during the winter season has been 4.6 degrees Fahrenheit, over 10 degrees warmer than for 1954-1996.
The final graph (Figure 3) shows an 11 year running average for winter time minimum temperatures observed at London for the period 1959-60 to 2006-07. In this graph for any given winter, the temperature plotted is the average minimum temperature observed during the 11 year period centered on that winter. For example the -7.7 plotted for the winter of 1959-60 indicates that for the 11 winters from 1954-55 through 1964-66 the average coldest temperature observed each winter was -7.7.
The final chart may be the most revealing of all, as it averages out the year to year variability in winter time minimum temperatures, and shows how average winter time minimum temperatures have been rising at London for much of the past 3 decades.
Figure 1. Coldest temperature observed each winter at Jackson from 1981 to 2012.
Figure 2. Coldest temperature observed each winter at London from 1954-55 through 2012.
Figure 3. Average coldest temperatures observed for 11 year periods centered on each winter from 1959-60 to 2006-07.