I would like to start with what we know about tornadoes and outbreaks, and what would cause such catastrophic events, like the outbreak that occurred produced on November 17 in the Midwest. Midwest, part of the United States. Tornado outbreaks occur when multiple tornadoes are believed to be produced by the same weather system. The classification of an outbreak may vary depending on interpretation. It is said that to be classified as a "tornado outbreak", a certain number of tornadoes must touch down. The United States is said to be the country with the most tornadoes. This can be attributed to the mid-latitude location. The Rocky Mountains have the ability to lock in moisture and “loop” atmospheric flow; thus forcing a lot of dry air into the mid-levels of the troposphere, due to descending winds. While the Rockies form a “dry line,” the Gulf of Mexico, on the other hand, brings a lot of moisture to low altitudes. This mixture of warm and cold air is responsible for the large number of tornadoes that form in the United States. These events are most prevalent in the Midwest and Southeastern United States, as well as the Great Plains, also known as (tornado alley), although some of these systems have been known to travel as far north than Canada. The tornado outbreak that occurred on November 17 is considered one of the largest outbreaks in eight years. This particular storm spawned a total of 72 tornadoes that swept through seven states, according to the National Weather Service. This outbreak is considered the fourth largest outbreak of its kind, especially at this time of year. This epidemic covered a vast area; just to give an example, there was...... middle of paper......t-tornado-outbreak/20074227 http://en.wikipedia.org/wiki/Tornado_outbreak Glickman, Todd S (ed.) (2000). http://www.crh.noaa.gov/ind/?n=nov172013outbreak http://www.accuweather.com/en/weather-news/how-rare-was -midwest -tornado-outbreak/20074227 http://en.wikipedia.org/wiki/Tornado_outbreak Glickman, Todd S. (ed.) (2000). Glossary of Meteorology (2nd ed.). American Meteorological Society. ISBN 978-1-878220-34-9. ^ Grazulis, Thomas P. (1993). Major tornadoes 1680-1991: chronology and analysis of events. St. Johnsbury, VT: The Tornado Environmental Film Project. ISBN 1-879362-03-1. Jump up ^ Galway, Joseph G. (1977). "Some climatological aspects of tornado epidemics". Mon. Weather Rev. 105 (4): 477-84. Bibliographic code: 1977MWRv..105..477G. doi:10.1175/1520-0493(1977)1052.0.CO;2. http://www.noaanews.noaa.gov/2011_tornado_information.html