 There were 1,709 tornadoes in 2011, falling short of the record
1,817 tornadoes set in 2004. In comparison, the average number of
tornadoes over the past decade is around 1,300.Last year ranks as
the fourth-most-deadly tornado year ever recorded in the United
States.
In 2011, there was a very strong La Niņa, a phenomenon where the
sea surface temperatures in the central and eastern Pacific around
the equator are below normal. As a result, there was a very strong
jet stream, which is a key ingredient for severe weather.
Often in a La Niņa year, the "Tornado Alley" shifts to the east,
spanning the Gulf states, including Mississippi and Alabama, and the
Ohio and Tennessee valleys. During the extremely active severe
weather season of 2011, many tornadoes touched down east of the
typical Tornado Alley, which stretches from Texas to Kansas.
Twisters frequently hit Texas to Kansas during the spring as warm,
humid air from the Gulf of Mexico clashes with drier air coming out
of the Rockies.
Above-normal tornadoes are anticipated again this year.
Warmer-than-normal Gulf of Mexico water is a key component to the
active severe weather season anticipated in 2012. There will be a
sufficient supply of warm and humid air to fuel supercell
thunderstorms, the type of storms that spawn strong tornadoes,
because of the warm Gulf water. (See graphic
below.)
The weak to moderate La Niņa during this winter is much weaker
compared with last winter, and it is weakening even more now. There
is evidence that warming is occurring in the equatorial Pacific, so
the El Niņo/La Niņa Southern Oscillation, or ENSO, is expected to
turn neutral by April. In other words, the temperatures in the
central and eastern equatorial Pacific will be near normal by
spring.
"Areas that seemed to miss out on frequent severe weather last
year may see an uptick this year," said Dan Kottlowski, expert
senior meteorologist for AccuWeather.com, regarding the difference
in pattern.
The mid-Mississippi and upper Ohio valleys are among the zones
that may get hit more frequently by severe weather this year.
Missouri, Illinois, Indiana and Michigan are included in this zone.
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It is highly unlikely that the same areas of the Deep South that
were struck by tragic tornado outbreaks in 2011 will be hit as hard
again this year. (See photo below.) However,
there could be some damaging thunderstorms and tornadoes in the Gulf
states this season.
The Deep South, including the Gulf states and eastern Texas, is
expected to get hit by severe weather early in the season, mainly in
March. By early April, the severe weather threat will retreat to the
north, reaching the lower Ohio and mid-Mississippi valleys,
according to Paul Pastelok, expert long-range meteorologist and
leader of the AccuWeather.com Long-Range Forecasting Team.
"If I were in the South or Ohio Valley, I'd be extra prepared
this year," cautioned Mike Smith, senior vice president of
AccuWeather Enterprise Solutions.
Whether tornadoes hit highly populated areas like they did last
year is harder to pinpoint.
"There is no way to know if it (2012) will be as active as last
year. Last year we had two unfortunate occurrences simultaneously: a
larger-than-normal number of tornadoes, plus tornadoes hitting
densely populated areas. There is no way to know if the cities are
going to be hit in the same number as last year. If so, it could be
another deadly year," Smith said.
[Text from file received from
AccuWeather.com; written by Meghan Evans, meteorologist writer]
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