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Severe Weather. A Scientastic presentation. Storm Chaser’s Cli p. http:// www.discovery.com/tv-shows/storm-chasers/videos/what-is-the-dominator.htm Discussion Question –. Severe Thunderstorms. C apable of producing: heavy downpours and flash flooding
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Severe Weather A Scientastic presentation
Storm Chaser’s Clip http://www.discovery.com/tv-shows/storm-chasers/videos/what-is-the-dominator.htm Discussion Question –
Severe Thunderstorms • Capable of producing: • heavy downpours and flash flooding • Strong, gusty straight-line winds • Large hail • Frequent lightning • Tornadoes • For a thunderstorm to be officially classified as severe: • winds in excess of 93 kilometers (58 miles) per hour • produce hailstones with diameters larger than 1.0 inch or generate a tornado. • about 10 percent (10,000 storms) reach severe status.
Life Cycle of Thunderstorms Cumulus Stage • Dominated by rising currents of air (updrafts) • Formation of a towering cumulonimbus cloud • Falling precipitation within the cloud causes drag on the air and initiates a downdraft • The downdraft is called an entrainment
Life Cycle of Thunderstorms Mature Stage • Downdraft leaves the base of the cloud and this releases the precipitation • Gusty winds, lightning, heavy precipitation, and sometimes hail • The most active period of a thunderstorm.
Life Cycle of Thunderstorms Dissipating • Dominated by downdrafts • Without a supply of moisture from updrafts, the cloud soon evaporates
Squall Lines • Contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and waterspouts • Form in unstable atmospheric environments where low-level air can rise • Heat is released during condensation • Causes the rising air becoming lighter than nearby air at the same height. • This leads to an increase in the speed of the rising air (up to 30 mph) • The gust front • where these winds meet • extends from the surface well up into the storm A squall line is a line of severe thunderstorms that can form along and/or ahead of a cold front.
Super cells Super cell is a large rotating thunderstorm with a mesocyclones • Can last longer than normal thunderstorms • Can produce tornadoes and baseball size hail. Mesocycloneis a large rotating vortex of air • Rotate in the same direction as a low air pressure system • Formed when wind shear starts a portion of air in the lower atmosphere spinning in a tube • In the tube the air is rotating around a vertical axis.
Super Cells Components of a Supercell • The overshooting top is a dome shaped formation on the top of a supercell • Theanvil is the overshooting portion at the top of the supercell(cold, dry) • Theprecipitation free base is a portion of the supercell without precipitation • Thewall cloud is the portion of the super cell between the precipitation free base and precipitating areas
Lab – Make Your Own Cloud http://www.kidspot.com.au/kids-activities-and-games/science-experiments+10/how-to-make-a-cloud-in-a-jar+12511.htm
Tornados Tornadoes are large clouds mostly characterized by extremely high winds • Usually found in the most intense super cells and are caused by winds traveling in different directions • Look like large funnels touching down from the main cloud • Afunnel cloud may or may not occur with a tornado • Damage caused by a tornado can be related to the high • Hazards include downed power lines, broken gas lines and pumps, and fires
Formation of Tornados • Formation • The rotation of winds within a meso cyclone allows a vortex to form • A funnel cloud usually forms • Gains energy as it descends • Becomes a tornado once it touches down • Maturity • When it becomes a tornado • Where all the destruction comes in. • Dissapation • Meso cyclone loses its rotation • Begins to dissipate • Shape of the tornado can be altered
Water Sprouts Waterspouts are similar vortexes that occur over water. They are usually less violent than regular tornadoes, although they can be rather powerful given a strong storm
Fujita Scale An F6 category was also thought of, but it is purely hypothetical and no F6 tornado has actually existed.The Enhanced Fujita Scale was intended to improve the Fujita scale. Both scales measure the severity of tornados.
Lab – Make Your Own Tornado http://www.kidspot.com.au/kids-activities-and-games/science-experiments+10/tornado-in-a-jar-experiment+12759.htm
Lightning Discussion Questions • Does lightning start from the cloud and move down, or does it start from the ground and move up? • Does every thunderstorm have lightning?
Lightning Formation - Causes • A storm is only classified a a thunderstorm when there is lightning • Positively charged ions are concentrated in the colder regions of the droplets, whereas negatively charged ions are concentrated in the warmer regions. Thus, as the droplets freeze from the outside in, they develop a positively charged ice shell and a negatively charged interior. As the interior begins to freeze, it expands and shatters the outside shell. The small positively charged ice fragments are carried upward by turbulence, and the relatively heavy droplets eventually carry their negative charge toward the cloud base. As a result, the upper part of the cloud is left with a positive charge, and the lower portion of the cloud maintains an overall negative charge with small positively charged pockets. As the cloud moves, the negatively charged cloud base alters the charge at the surface directly below by repelling negatively charged particles. Thus, the surface beneath the cloud acquires a net positive charge. These charge differences build to millions and even hundreds of millions of bolts before a lightning stroke acts to discharge the negative region of the cloud by striking the positive area of the ground below, or, more frequently, the positively charged portion of that cloud, or a nearby cloud.
