Source Regions and Pressure Systems

Air Mass A large body air where temperature and moisture content are similar throughout. Air masses form over large land or water masses.

Source Region Moisture content and temperature are determined by the area over which the air mass is formed called a source region.

Air masses are designate by a two letter system.

The first letter indicates the moisture content. -Continental forms over continents - Maritime forms over oceans

Continental - Means land. A Continental air mass forms over land.

Maritime - Means water. Maritime air masses form over water.

The second letter represents temperature. - Polar - Cold air masses - Tropical - Warm air masses

Polar Polar means it forms over the poles. COLD!

Tropical Form over the tropics (near the equator) WARM!!

Whether an air mass is warm or cold depends on the temperature of the source region. 4 types of air masses. Tropical – warm air masses that form over the tropics. Polar – cold air masses that form over the poles. Maritime – air masses that form over the ocean (very humid) Continental – form over land – (are dry)

Cold Air Mass There are three polar air masses that influence the weather in the United States. Continental polar Maritime polar: over the North Pacific Ocean Maritime polar: over the North Atlantic ocean

Warm Air Masses There are three warm air masses that influence the weather in the United States. Maritime tropical: that develops over the Gulf of Mexico Maritime tropical: that develops over the South Pacific Ocean Continental tropical

Complete the Source Region Map You have every vocabulary word you need to complete the source region map. ON YOUR OWN, put the words into practice and complete the map.

Pressure Systems

High Pressure vs. Low Pressure Think about your ears popping! Why do our ears pop? When do our ears pop?

To release pressure! Air moves in pressure systems very similarly to how the air moves when our ears “pop”!

Cold Vs. Warm Cold air Warm air

Pressure Systems Go back and think about the convection cells we created for Global Winds…..

How does air move?!? Air moves from an area of high pressure to an area of low pressure . High Low

High Vs. Low Pressure How will the air move? How will the air move?

Low pressure causes LIFTING High pressure causes SINKING

Low pressure is caused by WARM RISING AIR High pressure is caused by COLD SINKING AIR Low pressure is caused by WARM RISING AIR

So now we can put it all together!

Weather Fronts

High and Low Pressure Systems https://www.youtube.com/watch?v=Un2bMX2RnXE

Pressure Systems and Weather What weather is associated with each pressure system? Think about high pressure and low pressure and discuss with your neighbor as to what type of weather you may see with each system.

High and Low Pressure Systems https://www.youtube.com/watch?v=3HAth0D0Pt4&t=10s

Pressure System Diagram On the next page we will put in an illustration.

Weather Fronts

Weather happens when… air masses meet but do not mix due to different temperatures and moisture content becomes a front.

Fronts Fronts are the boundary between air masses of different temperature and moisture content.

Fronts 4 kinds of fronts: Cold front Warm front Occluded front Stationary 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.

Cold Front Rapidly moving cold air mass runs into a slowly moving warm air mass. The denser cold air slides under the lighter warm air pushing it upward. The rising air cools and condenses, forming clouds. Heavy rain or snow may fall. If the warm air mass contains only a little water vapor, there may be only cloudy skies. MAP TAP 2002-2003 Weather Fronts

Air gets drier after a cold front moves through Fronts: Five Types of Fronts 1. Cold Front: The zone where cold air is replacing warmer air Air gets drier after a cold front moves through NSF North Mississippi GK-8

Cold Front Cold fronts move quickly and can cause abrupt weather changes including violent thunderstorms After a cold front passes through, cool, dry air moves in. Clear skies and cooler temperatures often follow. MAP TAP 2002-2003 Weather Fronts

Warm Front Warm air mass collides with a slowly moving 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

Warm Front Moving warm air mass collides with a slowly moving cold air mass. The warm air moves over the denser cold air. If the warm air is humid, showers and light rain fall along the front where the warm and cold air meet. If the warm air is dry scattered clouds form. MAP TAP 2002-2003 Weather Fronts

Air gets more humid after a warm front moves through Fronts: Five Types of Fronts 2. Warm Front: The zone where warm air is replacing colder air Air gets more humid after a warm front moves through NSF North Mississippi GK-8

Warm Front Because warm fronts move more slowly than cold fronts, the weather may be rainy or foggy for several days. After the warm front passes, the weather is likely to be warm and humid. In winter, warm fronts bring snow. MAP TAP 2002-2003 Weather Fronts

Comparing Warm and Cold Fronts Cold fronts move faster than warm fronts. The weather activity in a cold front is often violent and happens directly at the front. Cold fronts have sudden gusty winds high in the air creating turbulence. The weather activity in a warm front generally happens before the front passes. In a warm front the cloud formation is very low often creating situations of poor visibility. MAP TAP 2002-2003 Weather Fronts

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

Occluded Fronts A warm air mass is caught between two cooler air masses. The denser cool air masses move underneath the less dense warm air and push it upward. The temperature near the ground becomes cooler. MAP TAP 2002-2003 Weather Fronts

Occluded Fronts The warm air mass is cut off, or occluded, from the ground. As the warm air cools and its water vapor condenses, the weather may turn cloudy and rainy or snowy. MAP TAP 2002-2003 Weather Fronts

Fronts: Five Types of Fronts 4. Occluded Front: Formed when a cold front overtakes a warm front This occurrence usually results in storms over an area In U.S., the colder air usually lies to the west NSF North Mississippi GK-8

Stationary Fronts A front that stops moving or is moving very slowly. Shown on a weather map with alternating red semicircles pointing away from the warm air and blue triangles pointing away from the cold air. MAP TAP 2002-2003

Stationary Fronts Sometime cold and warm air masses meet, but neither has enough force to move the other. They meet in a “standoff” MAP TAP 2002-2003 Weather Fronts

Stationary Fronts Where the warm and cool air meet, water vapor in the air condenses into rain, snow, fog, or clouds. It may stall over an area and bring many days of clouds and precipitation. MAP TAP 2002-2003 Weather Fronts

Fronts: Five Types of Fronts 3. Stationary Front: When either a cold or warm front stops moving When the front starts moving again it returns to either being a cold or warm front NSF North Mississippi GK-8

Locate the 4 types of fronts on this weather map.

Cold Fronts

Warm Front

Stationary Front

Occluded Front

Be a Weather Forecaster You are planning to travel to Alabama in 2 days. The high temperature there for today is 68º F. Use the map to help you predict whether the temperature in Alabama will increase, decrease, or stay the same. Explain why you think so. Weather Fronts

Be a Weather Forecaster There is a cold front approaching. The temperatures will probably be cooler behind the front.

Be a Weather Forecaster Of course, meteorologists (weather forecasters) use much more data than fronts and air masses to help them forecast the weather more accurately. But any forecast is just a prediction of what might happen. Even with the best data, weather forecasts can be wrong. MAP TAP 2002-2003 Weather Fronts