MJO Waves and USA Tornadoes


Large tornado 24 May 2016 south of Dodge City, KS by Juston Drake & Simon Brewer

The Madden-Julian Oscillation (MJO) has been accepted by many meteorologists and long-range forecasters as an atmospheric teleconnection with a significant impact on global atmospheric patterns.  A relatively strong and progressive MJO wave can temporarily change a large-scale seasonal atmospheric pattern over a region the size of a continent.  Sometimes a regional blocking pattern can be broken into a progressive pattern by an MJO wave.

I first took notice of the importance of MJO waves during the Summer and Fall of 2005. The very active 2005 Atlantic Hurricane Season was significantly affected by strong progressive MJO waves.  Since then I’ve kept an eye on MJO Indices during the Hurricane Season.  A few years later, I also began to see the importance of how MJO waves affect winter and severe weather patterns over the United States.

A rapidly dying strong El Nino mostly dominated the pattern over western North America this Spring.  My good friend, a professional long-range forecaster and meteorologist Jim Bishop, felt this pattern was conducive for a large ridge over the Western U.S. and troughing over the Northeast throughout the Spring.  He suggested the biggest reason for temporary breaks in this pattern was possibly caused by MJO waves. After pretty much hanging up my gear for the Spring-early Summer severe weather season I took a look at the data to see if there were any correlations between the MJO and patterns conducive for USA tornadoes.

My research was simple:  I looked at the reported USA tornado graph from the Storm Prediction Center (SPC).  I located dramatic increases in the 2016 tornado count I refer to as “tornado surges”. I, also, located MJO Waves during the year 2016 on the 15-day Mean MJO Index from the Climate Prediction Center (CPC).  I created rough plots of the tornado surges on the MJO Index chart with MJO waves circled (SEE ATTACHED IMAGE BELOW).

2016 MJO Index via CPC & USA Tornado Chart via SPC

2016 MJO Index via CPC & USA Tornado Chart via SPC

What I found was very interesting. I expected to see a moderate correlation in the data, but instead, found a relatively strong one.  I subjectively determined there to be 6 tornado surges from January to mid-July of 2016.  I determined there to be 5 progressive MJO waves during that period, excluding a strong MJO wave in late December into early January.  It appears the 5 MJO waves matchup with 5 of the 6 tornado surges during the Spring and Summer of 2016.  This suggests there was a reasonably strong correlation between MJO Waves and the atmospheric pattern conducive for surges in the number of USA tornadoes during the Spring and Summer of 2016.

It’s important to note I only looked at the time period between January and mid-July of 2016.  I haven’t looked at any other years where other teleconnections may play a much different role in the large-scale atmospheric pattern over the USA. Also, this doesn’t suggest in any way that MJO waves create or cause patterns favorable for USA tornadoes. There are several big and many small atmospheric signals that affect global atmospheric patterns.

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