Severe Weather in Bolivia

Tornadoes are able to form in regions where there is strong vertical wind shear. The wind speeds for a tornado range from 70 to 300 mph and the pressure can be as low as 900 mb.  They usually are formed in big thunder storms.  Some requirements that a tornado needs to form is cold outflow of air from downdrafts that does not undercut the updraft.  The strong vertical wind shear is what helps to create the horizontal spin, and then when the air is lifted, it begins to rotate.  Tornadoes become mesocyclones when the rotating air column exceeds 5 to 10 km diameter.  This just shows that the scale of the tornado is large enough to fit in the mesoscale criteria.

      In the Unites States tornadoes usually travel to the northeast.   The reason this is because the majority of tornadoes are formed east of the Rocky Mountains also the predominant winds in the Northern Hemisphere are Westerlies which drives the tornadoes east. Tornadoes do not happen in Bolivia because it is very mountainous in Bolivia.  There are 1,200 tornadoes in the US on average. < http://www.noaa.gov/features/protecting/tornados101.html  >  The average number of tornadoes in Bolivia is zero.  This website lists all the tornadoes to happen in South America and Bolivia was not on it.  <http://en.wikipedia.org/wiki/List_of_Southern_Hemisphere_tornadoes_and_tornado_outbreaks#South_America >

http://en.wikipedia.org/wiki/Tornado_climatology#mediaviewer/File:Pasillo_de_los_tornads_de_Am%C3%A9rica_del_Sur.jpg

The picture above shows the zone of tornadoes in South America.  The gray zone is high risk and the red zone is medium risk areas.  Bolivia is in the top right of this picture and is not affected by the tornadoes. 

Based on this graph it seems like tornadoes have been increasing over time.  This could be inaccurate because the first dates on this graph date all the way back to the 1950’s.  Back then they didn’t have the same advanced tools and technology to measure tornadoes as we do now, which could be one reason why it seems to be increasing over time.

The three main requirements for hurricane to form are usually over tropical waters where the winds are light and water temperature is warm typically over 80 degrees F, and the humidity is high extending up through the troposphere.  Bolivia does not meet these requirements.  The continent is hardly ever struck with hurricanes. The reason for this is that there are many fronts and air masses that push the hurricanes more north.  Also the conditions in the South Atlantic Ocean are too hostile for hurricanes to form.  There are three main hurricane formation regions, and the word for a hurricane differs from what region in the world we are referring to. In the Atlantic and east pacific it is called hurricane. In the Indian Ocean and near Australia it is called cyclones, and off the coast of China and Indonesia it is called typhoons.

In the US hurricanes usually form in the Caribbean Sea and then travel to the northwest until they hit a large land mass.  Also the Westerlies push the storms back to the east which causes them to travel to northern Europe.  The few that make it onto US landmasses typically break up because of the friction with land and those that turn early and go back out to the Atlantic Ocean and break down because of cooler ocean temperatures.  There are no hurricanes that happen in Bolivia.  There are about 5 to 6 hurricanes that hit yearly. <http://www.aoml.noaa.gov/hrd/tcfaq/E19.html>  I couldn't find a website that said that there were no hurricanes, but this picture below shows that there has been no hurricanes that hit anywhere neat Bolivia.

http://www.bing.com/images/search?q=Hurricane%20History%20Map%20south%20america&qs=n&form=QBIR&pq=hurricane%20history%20map%20south%20america&sc=0-28&sp=-1&sk=#view=detail&id=D8DFF8AEEAA5EB091AD9F282DD8F5C977ABB4353&selectedIndex=2