Following a near-record number of tornadoes in 2011, an active severe weather season with above-normal tornadoes is expected in 2012.
There were nearly 1,700 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 Niña, 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 Niña 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.
The weak to moderate La Niña during this winter is much weaker compared to last winter, and it is weakening even more now. There is evidence that warming is occurring in the equatorial Pacific, so the El Niño/La Niña Southern Oscillation (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," AccuWeather.com Expert Senior Meteorologist Dan Kottlowski said 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.
It is highly unlikely that the exact same areas of the Deep South that were struck by tragic tornado outbreaks in 2011 will be hit as hard again this year. 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," Mike Smith, senior vice president of AccuWeather Enterprise Solutions cautioned.
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.
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