Why do some of the seasonal composite lines jump/jog on the charts?
When looking at a long term seasonal of a futures contract, it must be remembered that some contracts have not traded for the same period each year for the full history. The jogs in the lines just connect the seasonal patterns for the different periods. For example, a December contract may have traded only between June 1 and December 20 between 1980 and 2000, but from 2001 onward it has traded from March 1 to December 20. In a case such as this, you will see the seasonal line jog at the point where the additional 2001 trading period meets the shortened 1980-2000 trading period. For this example the seasonal line would possibly have a jog from May 31 to June 1. These jogs do not represent a jump or fall in the seasonal pattern, but merely connect periods where a different number of years of trading are available.
