So far in 2015, this year has been the slowest for tornadoes in the U.S. in over a decade, and would be the calmest in recorded history if it weren’t for a few severe weather outbreaks in Dixie Alley during January 1-4 right at the beginning of the year. Since that outbreak, there have only been a few tornadoes reported nationwide given the ridge the west and trough to the east that has dominated the climate pattern the second half of winter. Usually there are 36 tornadoes during February and 80 during March based on 1991-2010 averages and we’ve only seen 2… What does this mean for the rest of tornado season???
Based on this plot of annual tornado trends showing the 25th, 50th, and 75th percentiles as well as the lowest and highest outliers, I’d say we’re in for another below normal year like 2012-14… The 25th percentile curve has 36 tornadoes through the end of February, with 1196 tornadoes by the end of the year in the U.S., while the 75th percentile has nearly 90 tornadoes with 1389 by the end of the season. The most active year is represented by the red curve which I believe is 2004, with 262 tornadoes through February and just shy of 1900 by the end of the year for the most active in U.S. history.
While this limited analysis may show that 2015 likely will be a below normal year, check out the plot below that includes 2011. That year was very close to the 25th percentile as well by the end of February and March, but ramped up BIG-TIME with the most active April for tornadoes in U.S. history, including the infamous April 15 and 27, 2011 outbreaks. However, 2011 was a much different climate regime with cooler water basin-wide in the Pacific. With the El Nino conditions in the Tropical Pac, though, it may be enough “juice” to result in a more near-normal tornado season by end. We’ll see…
The state that receives the greatest number of tornadoes on average during March is Texas, by far, with 13, followed by OK, KS and the Dixie Alley States with 5 tornadoes (AR, MS, AL, GA, FL). Interestingly, California is one of the more active states during March with 2 tornadoes confirmed on average during 1991-2010. The Carolina Piedmont region is also an active location during late winter/early spring with 4 and 3 tornadoes on average, respectively for SC and NC.
Here are the averages by month for tornadoes in the U.S. for the year:
Is climate change leading to lower tornado counts in the U.S. with this ridge-trough pattern more common across North America???