Severe weather season, as it's often referred to by meteorologists, typically peaks during May, when meteorological conditions that lead to the development of dangerous thunderstorms are most abundant. These conditions -- including a sharp north-south temperature gradient -- have emerged early this year and, based on the expected weather pattern, will likely intensify in the coming months.
The same type of event occurred just last week, when there were 32 reports of tornadoes in the Tennessee Valley and Deep South on Thursday.
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Through Monday, there have been about 800 preliminary reports of damage from severe weather in 2011, more than 2.5 times greater than the number through the first two months of 2010. January and February 2010 generated 307 reports, including just one February tornado.
Thunderstorms and tornadoes develop out of a strong temperature contrast from north to south across the country, along with an ample supply of moisture from the Gulf of Mexico. Storm systems emerging from the Rockies and heading east ignite the meteorological fuel.
This is precisely the type of weather pattern that is expected to continue at least through May, which is when tornado season typically peaks.
The federal government's Climate Prediction Center forecast for March through May calls for temperatures that are likely to be warmer than average in the southern part of the country and cooler than average in the northern part of the country. Thus, the contrast will be more intense than in a typical year.
In addition, the storm track is expected to remain more active than normal because of the ongoing La Nina. This is one of the typical results of a La Nina: more storms moving out of the Pacific Northwest and northern Rockies into the Plains and eventually the eastern part of the United States than during a non-La Nina year.
That's been the case recently, and these storms have pulled moisture north from the Gulf of Mexico into the sharp temperature gradient, resulting in lines of dangerous thunderstorms. Last year, the tornado season started slowly, in part because it was cooler than average in the Deep South during the latter part of winter through the first part of spring.