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Chapter 20 – Weather I. Air Masses and Weather __________________– the study of processes that govern Earth’s Atmosphere A. Origin of an Air Mass 1. An Air Mass is a large body of air with the same _____________and _____________ 2. The humidity and temperature of the air mass is determined by where they _______________ i. Over a southern ocean – moist and warm 3. When the air mass travels, it takes with it the temperature and humidity of its place of____________. B. Origins of air masses 1. Classification due to where they form a. Continental Arctic (cA) – extremely _______and ___ Forms over land (continental) and cold temperature causes it to be ________. b. Continental Polar (cP) – _________ and _______ c. Maritime Polar (mP) maritime – moist; plus ______ and _____________ d. Maritime Tropical (mT) – _________and _______ e. Continental Tropical (cT) – ________ and _______ II. Fronts and Lows A. What is a front? 1. Front – Boundary that separates opposing air __________ a. Can range from 200 meters, to _______ kilometers b. Can be as high as ________ kilometers c. Can be as long as ________________ kilometers 2. Air masses on either side differ in ____________, temperature and ______________ direction. B. Kinds of fronts 1. Cold front – boundary between an advancing ______air mass and _______________ air mass it is displacing. a. Cold air denser therefore it slides __________the warm air in front of it, forming a __________ slope b. The precipitation along the cold front is usually heavy and fast (__________________) c. However, the passing front may cause no greater change than a shift in__________ _______________. 2. Warm front – boundary between an advancing ________ air mass displacing a ________________ air mass a. Warm air is less dense therefore, it _________ up over the cold air forming a _____________ slope. b. The first signs of an approaching _________ front are high ___________ clouds, which are followed by cirrostratus then lower _______________ clouds. c. Eventually nimbostratus clouds which give ______ rain or snow. 3. _______________ front – occurs when the faster moving cold front catches up to a __________ front. a. The _________ air gets pushed up between the two cold air masses causing cloudiness and ____________. 4. ________________ front – front is not moving forward a. May give many days of steady rain causing_______________. C. Life Cycle of a Mid-Latitude Low 1. _______air mass meets a _________ air mass in the mid latitudes 2. Circulation begins due to the warm air moving _______and the ____________southward (p. 442) 3. The circulation around the Low is __________________ in the Northern Hemisphere 4. This counterclockwise motion of a Low ________ air off the earth’s surface. Air is constantly spiraling into a ______________________________ system. 5. Throughs and Highs (p. 443) 6. __________ pressure is associated with _______________ weather. 7. _____________ pressure is associated with _____________ conditions. III. Thunderstorms and Tornadoes A. Thunderstorms – storms with lightning and thunder formed in __________________________ clouds. 1. The cloud can be as tall as ___________ 2. Formed in convection cells – warm air being lifted ___ while cool air __________ (p. 445) 3. Often form along _______ there may be many ______ 4. ____________ line – many thunderstorms along a ______ 5. Supercells – very large singlecell thunderstorm that can produce ______________ 6. Lightning – discharge of ___________ – cloud to cloud, cloud to ground. Can occur in thunderstorms, snowstorms, dust storms or volcanic eruptions. B. _______________ – byproducts of supercell thunderstorms 1. Violently rotating column of air 2. Tornado formation 3. Form from between the wall clouds of a_____________ (p. 447) 4. A tornado’s funnel cloud results when the air pressure at its center is very _________and air sucked into the funnel expands and cools; water vapor in the air condenses. C. Storm and Tornado watches and warnings 1. _____________ – conditions are right 2. _______________ – one has been spotted IV. Hurricanes and Winterstorms A. _______________ – huge rotating storm of tropical origin that has sustained winds of at least 119 km/h 1. Winds and rain are strongest at the ________wall 2. Hurricanes rely on the transfer of ________ from the ____________, they form only when surface ocean waters are sufficiently warm, and they weaken as soon as they make landfall. 3. ___________________ by global wind patterns 4. Storm ____________ results, in part, from strong winds of the eye wall which blows water into a ________________. 5. If storm surge strikes land the same time as high tide, hurricane disaster ______________. 6. Hurricanes are ranked according to the _________Simpson Hurricane Scale on p. 452 B. Winter Storms 1. Blizzard – must have winds higher than _______ , temperature ___________ or lower, and reduced visibility due to falling or blowing snow V. Forecasting Weather A. Gathering data 1. ____________________ – visible images and infrared a. Visible – the whiter the clouds the thicker – meteorologists can track the clouds to get _________ and ________________. b. Are not available at ____________ c. Infrared satellite – use temperature to plot ________ d. The cooler the cloud _________ the higher it is in the atmosphere e. Can be used at night 2. ____________________ – measure temperature, pressure and humidity of air at different altitude. a. Attached to a large balloon and tracked by _______ b. Identifies the shape of the __________ stream 3. Surface Observations a. Most are at _____________ b. Information can help to locate __________, highs and lows c. Provide – temperature, ________ point, barometric pressure, wind speed and direction, visibility, precipitation, height of clouds and the amount.