A few Accuweather.com Weather Forum members hanging out in the LRC 2011-12 thread were critiquing a pattern for the days of Sep-5 and Oct-19 taking on a similar look and feel at the 500mb level. This similarity begged the question of why/how could this be if the pattern sets up Oct through Nov. The simple answer is, when the jet meanders southward in Autumn the cycle begins to morph into an entirely new cycle and August and September hold clues to the new patterns taking hold during October and November. The cycle change is certainly not a discrete on-off switch from previous to new. Using the 500mb plots and following this particular pattern backward in time from the dates above I noticed, while these dates match up well, major differences come into play just 48 hours prior. The reason for the similarity is, I believe, the cycle was morphing into the new cycle while retaining similarities with the previous cycle.
(500mb Plot Sep-5, 2011)
(500mb Plot Oct-19, 2011)
Going forward it is very difficult for me to consider what happened after September 5th having any bearing on what we should expect October to bring. Similarities in the new pattern with the previous pattern do not come back until Oct-27 when Sep-22 takes on a similar look. Another potential morphing example.
(500mb Plot Sep-22, 2011)
(500mb Forecast Plot Oct-27, 2011)
Sometimes the 500mb plots don't do the trick in explaining the patterns within the cycle. Graphing the 500mb soundings for a location is also a very good way to gain recognition. In the graph below it is fairly easy to see the morphing effect as the actual 500mb heights derail from the average trend of several LRC cycles but then come back on track to only derail once again.
(500mb Soundings Sep-5 & Oct-19)
It is the time from October through November that the cycle regenerates (jet strengthens) leading us into the new cycle. Following along allows us to notice the signs of the previous cycle morphing into the new cycle. Amazing and very, very exciting! If there are any questions or thoughts on my research and analysis of the LRC or how I presented the material just let me know in the comments section of the blog. The 2011-12 LRC calendar can be found here and is also accessible from the LRC Analysis Tools section in the upper right portion of the blog. Thanks for reading!