Tornado Frequency vs. Similar SOI, NAO and PNA years to 2003-2004

        Tornado frequencies have an interesting connection to the Southern Oscillation Index (SOI), the North Atlantic Oscillation (NAO) and the Pacific/North American (PNA) index, providing a convenient way for meteorologists to give a general prediction of upcoing tornadic activity across the United States by comparing the current year's November, December and January indices to other years with similar values.  The three indices tell meteorologists something about pressure flow and how climatology may be affected, each index providing different predictors on things such as precipitation, pressure patterns and tornadic frequency.  As can be seen, tornadic activity increases as the summer months progress, with years after 1976 (the last major atmospheric regime change) being, on average, more active.  It should also be noted that years matching 2003-2004's PNA values are among the highest in regards to tornado frequency, corresponding to the spike in tornadic activity for 1995's May 510 tally.  The prediction can therefore be made that this year should see an increased number of tornadic events across the US.  Below is a table with total number of tornados for each month, as well as the departure from normal and which index the particular year matched for the 2003-2004 period.

-Brandon Katz