Alabama Tornado Trends

Last year, Alabama experienced one of the busiest severe weather seasons of all time.  When the calendars were flipped to 2012, many hoped we would be turning a new leaf.  For the most part, so far, this has become a reality.  2012 has been a relatively quiet year severe weather wise.  January started off pretty busy with 13 recorded tornadoes (11 on January 23rd in central Alabama), but since then, only 21 more have occurred.  This total of 34 through Thanksgiving Day 2012 is below normal (about 40 total per year) for Alabama.  In fact, if we remain tornado-free through the remainder of the year, 2012 will conclude with the lowest tornado total since 1999 (23) and give us the 29th lowest total tornado count since 1950.  With this low number, we thought we'd take a look at where the state stands in the grand scheme of tornado trends.  This first graph illustrates where 2012 ranks compared to the last several years.

annual tornado trends

This next graph illustrates where the last several years stand in relation to normal (around 40 tornadoes per year).

Departure from Normal

The graph below shows the breakdown of where 2012 ranks in percentiles. These totals have been calculated and are weighted by the F-Scale rating of the recorded tornadoes. An inflation adjustment was done only to F0 and F1 tornadoes. The reports of F2-F5 tornadoes since 1950 has remained virtually flat, and the increase in tornado reports overall has been due to more F0 and F1 tornadoes being reported during this time. 

F-Scale Weight Tornado Trends

The following chart shows this trend of increasing tornado reports in another way.  
 

Weak versus Strong Tornadoes

 

The yellow dotted line shows the trend of F2 and stronger tornadoes since 1950.  This trend has essentially remained flat over the last 62 years.  Notice the upward trend of weaker tornadoes in this same time frame, indicated by the dashed white line.  This can be directly related to a number of factors, including improved radar technology for tornado detection, as well as improved technology for severe weather reporting since the late 1990s.  With the advent of social media outlets in the last 10 years, being able to get tornado reports to the National Weather Service has increased tremendously.

For a similar comparison of U.S. tornado trends, click here.

Thanks to Mark Linhares and Jim Westland for the statistical compilation. 


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