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Chapter 16 Air Masses and Fronts Air forms in large clumps and move over the Earth’s surface and slowly change. These huge bodies of air that cover thousands of kilometers are called AIR MASSES. An air mass has some of the same general properties as the land or water that it forms over. Two Properties of air masses are: 1. Moisture content 2. Temperature Air Masses •A huge section of air from the lower troposphere that has the same kind of weather throughout Air Mass • A large body of air where temperature and moisture content are constant throughout. • Illustrate a picture to represent this statement/definition. Types of air masses •mT –Maritime Tropical Warm Moist Air usually over tropical waters Maritime Tropical • Air mass brings warm humid air from the south Pacific ocean to California and Southwest. • Air mass brings warm humid air from the Gulf of Mexico and south Atlantic Ocean. •mP –Maritime Polar Cold Humid air coming from over cold ocean waters Maritime Polar • From Pacific ocean brings cool, humid air to the East Coast. • From North Atlantic ocean brings cool humid air to the West Coast. •cT –Continental Tropical Hot dry Air originating over desert areas Continental Tropical • Brings hot and dry air from Southern and Northern Mexico to Northeast and Southern Great plain states. Continental Polar • Brings cold and dry air from over Canada and Alaska to Central and Eastern United States. •cP –Continental Polar Cold dry air coming from high latitudes Name the air mass that will influence our weather. When 2 air masses meet, they do not mix. What happens is that they form a border that is known as a front. Most of the weather that we think of happens along fronts. Fronts •Any Boundary between two different air masses •Generally means a change in weather •Four Types Notice the speed of the cold front… Cooler Temperatures Cold Front Facts • Occurs when a fast moving cold air mass overtakes a warm air mass. • The warm air is forced violently upwards, causing rapid cooling, vertical cloud development, and cumulonimbus clouds. • Often violent thunderstorms but short lived heavy rain. • Cooler temperatures behind the front. Cold Front Cold Front • A cold air mass is replacing a warmer air mass. • Shown on a weather map by a blue line with triangles pointing the direction the cool air is moving. Back to activity Cold Fronts A cold front forms when a cold air mass catches up to a warm air mass. Colder air is forces the warm air higher into the atmosphere. This warm air that is pushed up cools and forms clouds. This reaction causes rain to develop and thunderstorms also occur along a cold front. Notice the This speed of area is the cold where front… the TStorms are during this front. Green is rain. Notice the speed of the cold front… Cooler Temperatures Warm Front Warm Front Facts • This front occurs when a slow moving warm air mass overtakes a cold air mass. • The slope on this front is gradual, not steep like the cold front. • This slope promotes horizontal development of clouds and long steady rain. • High cirrus is usually seen before the warm front arrives. • Clear & warm weather follow this front Warm Front Warm Front Back to activity • Warm air mass replacing a cooler air mass. • Shown on a weather map by a red line with half circles pointing the direction the warm air is moving. MAP TAP 2002-2003 Weather Fronts 27 A warm front is when a warm air mass catches up to a cold air mass. ( Just the opposite of a cold front.) Warm air slides over the cold, dense air. This also causes clouds to form, but many miles ahead of the front. As the front approaches and passes it can cause steady rain or snow to fall. After all of this happens, the sky becomes clear (without clouds) and this is also when the temperature starts to rise (get higher). There it is, and this is the area of steady rain. Stationary Front Stationary Front Facts • The front is not in a hurry, it is very slow or not moving. • This front occurs when a cold air mass collides with a warm air mass and does not move. • None of the air masses are overtaking the other. • This usually means really long periods of clouds and steady precipitation. • The symbol for this front is alternating blue triangles and red half-circles facing in opposite directions. Stationary Front A front that stops moving is called a stationary front. This type of front can stay in the same place for days. When this front stays in the same place for a long time there is constant snow or rainfall and this leads to several inches of snow or it could even cause a flood. Occluded Fronts • When a warm front is trapped by 2 cold fronts. • Shown on a weather map by a purple line with alternating triangles and semicircles pointing the direction the front is moving. MAP TAP 2002-2003 Weather Fronts 34 Occluded Front Facts • Very violent type of front. • This is when 2 cold air masses “pinch together” and force a warm air mass off of the ground and higher • Rapid vertical and horizontal development occurs and violent storms are created. • Long and heavy rain with thunder storms. • The symbol for this front is alternating purple triangles and half-circles pointing in the direction that the front is moving. Occluded Front Where are the Fronts? L Where are the Fronts? L H L High pressure brings dry and clear weather Low pressure brings clouds and rain There it is, and this is the area of steady rain. So what did you learn? Summarize information about air masses and fronts on your paper.