AIR MASSES AND FRONTS

Do Now Which of the layers of the atmosphere experiences the greatest amount of pressure? Which of the layers of the atmosphere is the farthest away from the earth? Which layer of the atmosphere is the warmest? Which layer of the atmosphere does weather occur in?

AIR PRESSURE What is air pressure? Air pressure is the amount of water vapor particles in the air More particles = greater air pressure Less particles=limited air pressure Travels from high to low Is measured by a barometer Air masses are placed into one of two categories: polar(P) tropical(T).

TWO TYPES OF PRESSURE High pressure represented by a capital “H” the cause of good weather Low pressure represented by a capital “L” the cause of thunderstorms

An air mass is a large body of air that has similar temperature and moisture properties

Maritime tropical Air Mass (mT) Maritime tropical air masses (mT) form over the warm waters of the tropics and Gulf of Mexico. The northward movement of these air masses brings warm moist air into the United States                                            Maritime tropical Air Mass (mT)

Maritime polar (mP) are cool humid air masses form over the icy cold North Pacific and North Atlantic oceans.                                                                The air masses affect the west coast more than the east coast. In the summer they often bring rain, fog, and cool temperatures to the west coast

Continental Polar air masses (cP) are cold and dry due to their continental source region

Continental tropical (cT) is dry, warm air that forms only in the summer over dry areas of land

An air front is defined as the area between two air masses with different properties. Fronts extend not only in the horizontal direction, but in the vertical as well.                                                              

Cold Front A cold front is defined as the area where a cold air mass is replacing a warmer air mass. Cold fronts are dense because there is more water vapor present in the air. Cold fronts move from northwest to southeast. The air behind a cold front is colder and drier than the air ahead of it. When a cold front passes through, temperatures can drop more than 15 degrees within the first hour.                                                 cold front is represented by a solid blue line with triangles along the front pointing in the direction of movement

Warm fronts A moving warm air mass collides with a slowly moving cold air mass. Warm fronts are less dense because there is less water vapor present in the air. If the warm air is humid showers and light rain might fall along the front where the warm and cold air meet. If the warm air is dry scattered clouds may form. After a warm front passes through an area the weather is likely to be warm and humid. Winter warm fronts bring snow. Warm front is represented by a solid red line with circles along the front pointing in the direction of movement

Stationary Front Sometimes cold and warm air masses meet but neither one has enough force to move. Where the warm and cold air meet, water vapor in the warm air turns into rain, snow, fog, or clouds

Occluded Front When a warm air mass is caught between two cooler air masses and the thicker cold air masses move underneath the thinner warm air mass and push it upward As warm air cool and its water vapor condenses, the weather may turn cloudy, rainy or snowy

Now Let’s Check for Understanding! What’s the difference between a warm front and a cold front? Which forms faster, a warm front or a cold front? What type of weather is associated with warm fronts? What type of weather is associated with cold fronts? What happens at a stationary front?

What kinds of fronts appear here?

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What’s Goin’ On?

Comparing & Contrasting Cyclonic Systems With your table, complete a VENN DIAGRAM on hurricanes vs. tornadoes (Use your textbook - pages 573-577) →Each group will be responsible for writing one thing for the class consensus Venn Diagram on the board →at least 2 points comparing the two systems →at least 4 points on their differences. Consider: - speed - greatest damage - location of formation - time of formation/ predictability

Hurricanes Tornadoes

Comparing and Contrasting Tornadoes and Hurricanes Spinning systems of low pressure High speed winds

Hurricanes Boundary: Hurricanes are not associated with fronts Front Symbol Pre-Weather: Rain and wind, cloudy skies Post-Weather: Some rain, wind, and usually clear skies Pressure: 920-1000 mb Isobars: Wind speed: 74 - 210

Tornadoes Boundary: Tornadoes generally form at occluded fronts Front Symbol: Pre-Weather: Warm, humid air collides with cold, dry air Post-Weather: Mostly calm, potential for winds Pressure: 850 to 1000 mb Isobars: Wind speed: 40-318 mph

Questions? Clear your desks! Exit Ticket Time Questions? Clear your desks!