The Tornado Climatology of 2011

[Randy Zipser]

I have been reading the ST thread about the Joplin tornado and it got me thinking about why 2011 was such a prolific and deadly year for tornadoes across the United States. According to the Storm Prediction Center, 2011 logged 2,240 NWS Local Storm Reports (LSRs), which is about 61% above the 14-year (2010-2024) mean of 1,392 LSRs. To this day, 2011 remains the single most active year in terms of reported tornadoes. But what factors have contributed to that particular year being the lone standout?

The following articles discuss the climatological factors related to 2011:

2011 Tornado Season Climate Factors: NOAA Physical Sciences Laboratory

https://www.npr.org/2011/05/25/136657481/whats-behind-2011s-deadly-tornado-season

 

[Mike Smith]

Thanks for posting, Randy. I've often wondered what made 2011 so extraordinary but I don't find the PSL discussion particularly convincing.

There is a tendency, it seems, to want to tie events to the tropics which may have no connection. That may be why NWS 30 and, especially, 90-day forecasts are so bad.

 

[Randy Zipser]

There is a tendency, it seems, to want to tie events to the tropics which may have no connection

I also noticed that "connection," Mike.

Each tornado season is unique because whatever atmospheric/oceanic factors that contribute in the late winter/spring months differ from year-to-year. So whatever came together in the spring of 2011 never came together in quite the same way before 2011 and also has never repeated since. It may never happen again, or that record could be surpassed next season, who knows? At least Harold Brooks back in 2011 left that question open, rather than rushing to some explanation or conclusion (which was the right thing to do as an objective researcher).

For now, it seems that random, natural variability is best answer we can come up with...

 

[Boris Konon]

I also noticed that "connection," Mike.

Each tornado season is unique because whatever atmospheric/oceanic factors that contribute in the late winter/spring months differ from year-to-year. So whatever came together in the spring of 2011 never came together in quite the same way before 2011 and also has never repeated since. It may never happen again, or that record could be surpassed next season, who knows? At least Harold Brooks back in 2011 left that question open, rather than rushing to some explanation or conclusion (which was the right thing to do as an objective researcher).

For now, it seems that random, natural variability is best answer we can come up with...

One thing I have found, at least anecdotally, is that when the pattern is "good", it can be *really* good, and go off the scale, so to speak!

You look at the 759 tornadoes in April 2011 (one additional EF2 was just documented recently in AL), it is so far ahead of the #2-5 spots for monthly totals by 200-250! Quite an outlier. And no other April until 2024 had more than 300 tornadoes. All the biggest months were always May and June, so even more amazing.

Another example, more localized, in the 6-week period Jan-Feb 2015, eastern New England got buried w/ repeated big snowstorms. BOS had 93" snow in 30 days, by far its most in such a period on record, and avg seasonal snowfall is 49". Going through this living in ern MA, it was nuts. What I found odd was the repeated focus on just a small area of the region. Only RI, the eastern half of MA, and coastal NH/ME got record snowfall. There was sharp gradient W of here. Just to have repeated synoptic-scale low pressures take tracks that *only* favored this same small area I found fascinating. And what was even more odd, up until the 3rd week of Jan, snowfall had been very little for the region!