Sunday, 23 January 2011
The National Weather Service in Memphis has a mission to save lives and properties in their County Warning Area (CWA). This CWA includes West Tennessee, eastern Arkansas, northern Mississippi, and the 2 Bootheel counties of Missouri. This area is referred as the Mid-South. Some studies have shown nearly 10% of all the tornado deaths in the U.S occurred in the Memphis CWA. For this reason they decided to make a database about the tornadoes of the past years. A period of 27 years was hand analyzed from 1982 to 2009. In this period at least 246 weak tornadoes affected this area. The NCAR/NCEP reanalysis data were used to analyze the vector winds jet streaks at the 250 mb. The jets stream that passed through this area was studied to verify in which jet's quadrant the weak tornadoes can develop. Our results demonstrate that a weak tornado it's most likely to occur in the right side of the jet stream (entrance and exit sides). Also weak tornadoes are likely to develop when winds aloft aren't severe.
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