Monday, December 29, 2014

Good News: Nation Has Had A Three-Year Tornado Drought

Twin tornadoes rip through Nebraska in June. The mayhem
in this photo aside, 2014 will be the third year in a row
with fewer than the normal number of
tornadoes in the United States.  
Despite the Christmas week tornadoes in the South, and a possible tornado today in Georgia,  the year 2014 is going down as having among the fewest tornadoes in United States since at least the early 1950s.  

The two previous years also had a dearth of tornados.

Of course, you wouldn't think so, given some of the dramatic tornadoes in recent years, like the huge Moore, Oklahoma tornado in 2013 and the incredible double tornado that swept across part of Nebraska this past June.

But those are two of the highlights. The actual number of tornadoes is down. Way down.

On average, the nation gets about 1,260 tornadoes a year. So far this year, it's been closer to 900.

Most of the tornadoes that happen in the United States aren't those blockbusters you see on the news that destroy whole towns. Most of them are lower end, with winds of around 100 mph or less and don't last long.

Yes, they cause damage, but it's mostly in the form of damaged house roofs, broken windows, busted up barns and lots of toppled trees. It's stuff that makes the local news, but you won't see it on CNN.

There doesn't seem to be a hard and fast reason why the past three years haven't had many tornadoes. It probably has to do with chance more than anything else.

In 2012, as Capital Weather Gang notes, there was a big "heat ridge" over much of the nation that discouraged the moisture and the violent updrafts that create storms and tornadoes.

In 2013, there was a brief period in May, during which the Moore tornado hit, that was typical of the weather pattern that spawns tornadoes.

But that weather pattern didn't last as long as it often does.

In 2014, a chilly spring weather pattern discouraged tornadoes. Surges of hot, humid air moving northward from the Gulf of Mexico into colder air to the north is a key ingredient for tornadoes. We had few of those hot surges during the spring and early summer.

Unfortunately, we shouldn't count on the lack of tornadoes to continue. The number of tornadoes changes greatly year to year.

And we've been unlucky in the tornado department in recent years, too. The year 2011 brought the largest single outbreak of tornadoes in the United States on record around April 27 of that year.

The 350 or so tornadoes between April 25 and 28, 2011 killed 321 people and featured a much larger than normal proportion of violent twisters.

The year 2011 also featured a massive tornado that destroyed large swaths of Joplin, Missouri, killing 158 people and injured more than 1,000.

As you can, the tornado drought is one kind of "dry spell" the nation can embrace.

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