20 Weather 20.1 Air Masses and Weather 20.2 Fronts and Lows CHAPTER Weather EXIT CHAPTER 20.1 Air Masses and Weather 20.2 Fronts and Lows 20.3 Thunderstorms and Tornadoes 20.4 Hurricanes and Winter Storms 20.5 Forecasting Weather CHAPTER OUTLINE

20 20.1 Air Masses and Weather Weather CHAPTER Weather CHAPTER HOME 20.1 Air Masses and Weather VOCABULARY Scientists classify an air mass based on whether it originates in an arctic, in a polar, or in a tropical region and whether it forms over land (continental) or sea (maritime). meteorology air mass cA Continental Arctic very cold, dry mP Maritime Polar cool, moist mP Maritime Polar cool, moist cP Continental Polar cold, dry cT Continental Tropical hot, dry mT Maritime Tropical warm, moist mT Maritime Tropical warm, moist SECTION OUTLINE

20 20.2 Fronts and Lows Weather CHAPTER Weather CHAPTER HOME 20.2 Fronts and Lows VOCABULARY A front is the band of air between opposing air masses. Scientists classify a front based on the temperature of the advancing air mass — cold fronts and warm fronts. front cold front warm front occluded front stationary front Cold air Warm air Movement of the cold front Movement of the warm front SECTION OUTLINE

20 20.2 Fronts and Lows Weather CHAPTER Weather CHAPTER HOME 20.2 Fronts and Lows VOCABULARY Fronts are usually connected to mid-latitude low-pressure systems. Upper-level air flow influences the convergence or divergence of air into and out of pressure systems. The movement of fronts and lows greatly influence the weather at mid-latitudes. front cold front warm front occluded front stationary front Radar image of the eastern United States showing the weather associated with a low-pressure system. SECTION OUTLINE

20.3 Thunderstorms and Tornadoes CHAPTER Weather CHAPTER HOME 20.3 Thunderstorms and Tornadoes VOCABULARY thunderstorm squall line Thunderstorms form in warm, moist, unstable air. They produce lightning, a discharge of electricity. super cell lightning tornado 1. Cumulus Stage Air rises and a cumulus cloud forms. The rising air is called an updraft. The updraft prevents precipitation from reaching the ground. 0° 2. Mature Stage The precipitation becomes heavy enough to fall through the updraft and reach the ground. The falling precipitation creates a downdraft. 0° Heavy rain 3. Dissipating Stage The downdraft weakens the updraft, eventually cutting off the supply of moist air rising to the cloud. The cloud begins to evaporate. 0° Light rain SECTION OUTLINE

20.3 Thunderstorms and Tornadoes CHAPTER Weather CHAPTER HOME 20.3 Thunderstorms and Tornadoes VOCABULARY thunderstorm squall line Tornadoes can develop in thunderstorms containing rotating updrafts. super cell lightning Mesocyclone Inflow Tornado Wall cloud tornado SECTION OUTLINE Storms and tornadoes can cause severe damage.

20.4 Hurricanes and Winter Storms CHAPTER Weather CHAPTER HOME 20.4 Hurricanes and Winter Storms VOCABULARY hurricane storm surge Hurricanes are large, rotating storms originating over tropical oceans. They are classified based on wind speed. Saffir-Simpson scale blizzard Eye Eye wall Feeder bands SECTION OUTLINE

20.4 Hurricanes and Winter Storms CHAPTER Weather CHAPTER HOME 20.4 Hurricanes and Winter Storms VOCABULARY hurricane storm surge Hurricanes are large, rotating storms originating over tropical oceans. They are classified based on wind speed. Saffir-Simpson scale blizzard Winter storms are mid-latitude low-pressure systems that occur over land in the winter. Both hurricanes and winter storms can cause severe damage. SECTION OUTLINE

20 20.5 Forecasting Weather Weather CHAPTER Weather CHAPTER HOME 20.5 Forecasting Weather VOCABULARY Meteorologists must gather huge amounts of data in order to make their predictions. They rely on sensing instruments and on computer models to provide the information they need. station model Visible Satellite Image - Ohio Infrared Satellite Image - Ohio SECTION OUTLINE

20 20.5 Forecasting Weather Weather CHAPTER Weather CHAPTER HOME 20.5 Forecasting Weather VOCABULARY Meteorologists use the data to make surface weather maps and forecasts. station model Surface Weather Map SECTION OUTLINE

20 CHAPTER Weather CHAPTER HOME This is the end of the chapter presentation of lecture notes. Click the CHAPTER HOME button or exit the presentation.