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October 21, 2009 24-2 notes Fronts I. Front- a boundary several km long between 2 different air masses A. Types of fronts 1. cold front- happens when a cold air mass overtakes a warm one. What happens? moist warm air rises, cools condenses, rain cold front 2. Squall line - line of heavy storms that occur just ahead in the warm moist air fast moving, intense storms. Large cumulonimbus clouds form B. Warm fronts - cold air retreats from an area. More gradual slope. Cloud extend far ahead. high cirrus clouds, precip over a large warm front area C. Stationary front a front of air masses that moves either very slowly or not at all D. Occluded front-a front that forms when a cold air mass overtakes a warm air mass and lifts the warm air mass of the ground and over another air mass -all day rain Fronts video occualated link October 21, 2009 E. midlatitude cyclone an area of low pressure that is characterized by rotating wind that moves toward the rising air of the central low-pressure region Anticyclones the air of an anticyclone sinks and flows outward from a center of high pressure. The circulation of air is counter clockwise in the Northern Hemisphere. Anticyclones bring dry weather, because their sinking air does not promote cloud formation. October 21, 2009 SEVERE WEATHER A. Thunderstorm a usually brief, heavy storm that consists of rain, strong winds, lightning, and thunder thunder link Develop in 3 distinct stages 1. cumulus stage- warm moist air rises, air cools, condenses see puffy clouds 2. mature stage- Rain, cumulonimbus clouds 3. dissipating stage-strong downdrafts cause the air to stop rising. B. Lightning- clouds discharge electricity 1. Electricity heats the air, the air rapidly expands and lightning link produces thunder. 2. Upper part of cloud usually (-) lower par (+) charge. 3. Sound travels 1 km in 3 sec 1 mile in 5 sec 1100ft in 1 sec See lighting, how far is storm away when you hear thunder in 7.5 seconds? October 21, 2009 huricane pic C. Hurricane 1. A severe storm that develops over warm tropical oceans and Winds of more than 120 km/h spiral in toward the intensely low-pressure storm center called the ________ 2. Begins when warm, moist air over the ocean rises rapidly. 3. When moisture in the rising warm air condenses, large amounts of energy in the from of latent heat is released. This heat increase the force of the rising air. 4. Most dangerous aspect of a hurricane is a rising sea level and large waves, called a storm surge. October 21, 2009 D Tornadoes 1.tornado a destructive, rotating column of air that has very high wind speeds A. small, most violent, and shortest-lived severe storm B. How formed? A tornado forms when a thunderstorm meets high-altitude horizontal winds. These winds cause the rising air in the thunderstorm to rotate.A storm cloud may develop a narrow, funnelshaped rapidly spinning extension that reaches downward and may or may not touch the ground. pic Winds may reach speeds of more than 400 km/h. web link October 21, 2009 October 21, 2009 back October 21, 2009 October 21, 2009 October 21, 2009 First Page October 21, 2009 First Page October 21, 2009 back October 21, 2009 Back October 21, 2009 back