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TORNADOES are a low pressure storm that usually forms over land in an average year, 800 tornadoes are reported in the U.S. a tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground…the rotating column of air is called the vortex the vortex is only visible when debris and dirt gets carried up with the winds Where do they come from? Tornadoes come from the energy released in a thunderstorm. What makes them dangerous (as compared to hurricanes) is that their energy is concentrated in a small area, only a hundred yards across. When & Where do they occur? Most common east of the Rocky Mountains and west of the Appalachian Mountains. They occur mostly during the spring and summer (April-June) They usually occur during the late afternoon and early evening. Usually happen along cold fronts How long is a tornado usually on the ground? Can range from a few seconds to several hours ... 5 minutes is average How fast do tornadoes move? Movement can range from virtually stationary to more than 60 miles per hour ... average is 10-20 miles per hour. Do you know the difference? Watch—means conditions are favorable for tornado to develop Warning—means that a tornado has been spotted MEASURING DESTRUCTION The Enhanced Fujita Scale rates tornadoes based on the amount and type of wind damage produced. The Enhanced Fujita (EF) Scale EF-0. Light damage Wind 65 to 85 mph. Causes some damage to siding and shingles EF-1. Moderate damage Wind 86 to 110 mph. Considerable roof damage. Winds can uproot trees and overturn single-wide mobile homes. Flagpoles bend. EF-2. Considerable damage Wind 111 to 135 mph. Most single-wide mobile homes destroyed. Permanent homes can shift off foundation. Flagpoles collapse. Softwood trees debarked. EF-3. Severe damage Wind 136 to 165 mph. Hardwood trees debarked. All but small portions of houses destroyed. EF-4. Devastating damage Wind 166 to 200 mph. Complete destruction of well-built residences, large sections of school buildings. EF-5. Incredible damage Wind above 200 mph. Significant structural deformation of mid- and high-rise buildings. HURRICANES Low pressure systems that form over warm, tropical waters near the equator Most form between 5 and 20 degrees north latitude—they almost never form in the South Atlantic Different names are given to hurricanes depending on where they form 1. Atlantic—we call them hurricanes 2. Pacific—they are called typhoons 3. Indian Ocean—they are called cyclones Mature hurricanes average about 350 miles across They have the lowest barometric pressures ever recorded with any storm (905 millibars is lowest recorded) These huge air pressure differences is what creates the rapid, inward spiraling of winds HURRICANE DEVELOPMENT When winds have developed speeds from 39 to 73 miles per hour, it is called a tropical storm (storms are given names when they begin to have winds of this speed). The storm becomes a hurricane when it reaches a wind speed of 74 mph When a season is very active, Greek letters are used to name tropical storms after the letters of the alphabet had been used. END OF A HURRICANE When a hurricane travels over land or cold water, its energy source Retired Replacement (warm water) is gone and the storm weakens, quickly dying. Name Name Allison Andrea HURRICANE SEASON Floyd Franklin Georges Gaston Occurs from June through November Iris Ingrid Most hurricanes form during the late summer months because the Katrina Katia ocean is still retaining heat from the warmer earlier months Keith Kirk MEASURING DESTRUCTION Lenny Lee We use the Saffir-Simpson scale to rank hurricane intensities MichelleMelissa Saffir-Simpson Scale CATEGORY 1 2 3 4 5 WIND SPEED 74-95 mph 96-110 mph 111-130 mph 131-155 mph Greater than 155 STORM SURGE 4-5 feet 6-8 feet 9-12 feet 13-18 Greater than 18 DAMAGE Minimal Moderate Extensive Extreme Catastrophic STORM SURGE ACCOUNTS FOR 90% OF HURRICANE-CAUSED DEATHS AMAZING EARTH SCIENCE FACTS High pressure systems move clockwise and outward Low pressure systems move counterclockwise and inward.