An air mass is a large volume of air in which temperature and humidity are nearly the same in different locations at the same altitude Forms when air over a large region of Earth sits in one place for many days. Takes on the characteristics of the land below it.

Depend on the region where it forms. Ex.- a hot desert-a dry hot air mass; cool ocean water-moist, cool air mass Each category name is made of two words- one for moisture and one for temperature. The 1 st word tells if it was formed over water or dry land. It describes the moisture: Continental-forms over land Maritime-forms over water The 2 nd word tells if it was formed close to the equator. It describes temp. Tropical- forms near equator Polar-forms far from equator

Air masses can travel away from the region where they form When they travel they bring the characteristics with it Air mass can change slowly or quickly depending on speed of global winds

A front is a boundary between air masses Different types of fronts produce different patterns of weather The term “front” was first used by scientists during WW1 when compared to clashing air masses similar to armies chasing on the battlefield

Forms when a cold air mass pushes a warm air mass and forces the warm air to rise. As the warm air rises, its moisture condenses and forms clouds. Brief, heavy storms. Triangles show the direction that a cold front moves.

A warm front moves more slowly than a cold front. The warm air rises slowly over the cold air and its moisture condenses into flat clouds. Semicircles show the direction that a warm front moves.

A stationary front occurs when two air masses push against each other without moving. A stationary front becomes warm or cold when one air mass advances. Alternating triangles and semicircles show a stationary front.

Formed when air moves all the way around a high pressure center Most are large and change slowly Generally bring clear skies and calm air/gentle breezes

A large weather system that surrounds a center of low pressure. Begins as air moves around and inward toward the lowest pressure and then up to higher altitudes Can happen along boundaries of warm and cold air Air spirals around and moves in counter clockwise direction Stormy weather

Near the equator, warm ocean water provides the energy that can turn a low pressure center into a violent storm Tropical storm: low pressure systems that starts at equator and has winds that blow at 40 miles per hour Hurricane: tropical low pressure system with wind speeds of 74 miles per hour or greater Hurricanes that form over the Indian Ocean or western Pacific Ocean are called typhoons or cyclones

Need energy from warm water (80 degrees F) Can move in many directions but usually westward with trade winds As hurricane moves over land or cooler water it loses energy Center of hurricane is a small area of clear calm air- called the eye.

Can produce huge waves, strong winds and heavy rains Tornadoes can be generated When a hurricane moves into a coastal area, it often pushes a huge mass of ocean water known as a storm surge

Blizzards: heavy, deep snow with 35 miles/hour winds and very low temperatures Lake-effect snow storms: just east and south of the Great Lakes, moisture released as snow Ice storms: rain falls to ground then freezes, slippery roads

Warm humid air near the ground moves into cooler air above and rises quickly A thunderstorm is a storm with lightening and thunder Thunder is the effect of lightning

1. Rising humid air forms a cumulus cloud. The water vapor releases energy when it condenses into cloud droplets. This energy increases the air motion. The cloud continues to build into tall cumulonimbus clouds of a thunderstorm.

2. Ice particles form in the low temperatures near the top of the cloud. As the ice particles grow large, they begin to fall and pull cold air down with them. This strong downward draft brings heavy rain or hail-most severe stage of a thunderstorm.

3. The downward draft can spread out and block more warm air from moving upward into the cloud. The storm slows down and ends.

Flash Floods: can cause overflow of rivers, streams, lakes Winds: over 170 miles/hour Hail: can kill crops and livestock in minutes, damage livestock Lightening: can kill or cause serious human injury, damage power lines, spark forest fires

Tornado- Violently rotating column of air stretching from a cloud to the ground Tornadoes become visible when water droplets appear in the center of the rotating column. May lift dust and debris from the ground-bottom becomes visible A spinning column of air is not called a tornado unless it touches the ground. If it touches H2O instead, it is called a water spout.

They can lift or completely demolish sturdy building Moves along same path with a thunderstorm A tornado watch is issued when conditions might produce a tornado. A warning issued when a tornado has been detected

Meteorologists: scientists who studies weather Radar station: locates clouds and their heights, Doppler can detect air motion and precipitation Satellites: images can show cloud cover, warm and cool air regions and invisible water vapor Airplanes and ships: carries instruments that can take measurements Ground stations: measure air pressure, temperature, dew point, precipitation, wind speed, wind direction and cloud cover Weather balloons: measure air at different altitudes, can go into stratosphere Weather buoys: measure conditions in ocean that can affect atmosphere

The use of symbols and colors can show fronts, systems and precipitation

An isobar is a line that connects places that have the same air pressure Each isobar is labeled with the air pressure in units called millibars. Lines close together show a big difference in air pressure and strong winds are expected Lines far apart where the air pressure is almost even and expect calm or light breezes

This visible light satellite image shows clouds from above. The patches of white are clouds.

This infrared image also shows clouds but uses colors to show temperature and high or low clouds.

Meteorologists might observe clouds or weather conditions to infer that a front is approaching or use observations that have been collected and displayed on maps.