1. Air Masses and Fronts
How do Scientists classify the air masses that affect the weather in North America?
An air mass is a huge body of air with similar temperature, humidity, and air pressure throughout it.
Scientists classify air masses according to the temperature and humidity.
Tropical or warm air masses form in the tropics and have low pressure.
Polar or cold air masses form 50 degrees N and 50 degrees South.
Maritime air masses form over oceans and are humid.
Continental air masses form over land and in the middle of continents and are dry.

2. Air masses and fronts (continued...)
What are the main types of air masses? The four types of are:
Maritime Tropical
Continental Tropical
Maritime Polar
Continental Polar
What are the main type of fronts? Fronts are areas where air masses meet but do not mix.
Cold Fronts
Warm Fronts
Stationary Fronts
Occluded Fronts

3. Cyclones..
A Cyclone is a swirling center of low pressure. Cyclones are also called lows.
Cyclones and decreasing air pressure are associated with the storms and precipitation. Cyclones spin counterclockwise in the Northern Hemisphere.
Anticyclones are high-pressure centers of dry air. They are also called highs
Anticyclones bring dry, clear weather. Anticyclones spin clockwise in the Northern Hemisphere.
Anticyclone Cyclone…

4. Storms/Tornados Storm: Tornado:
A Storm is a violent disturbance in the atmosphere.
Thunderstorms form within large cumulonimbus clouds or thunderheads.
Lightning is a sudden spark or electrical discharge as positive and negative charges build up in the clouds.
Thunder is the sound of the explosion
During thunderstorms, avoid touching metal objects because they are good conductors of electricity.
Tornado:
A tornado is a rapidly whirling funnel-shaped cloud reaching from a storm cloud to earth’s surface.
Tornadoes develop in low, heavy cumulonimbus clouds.
Tornadoes occur most often is the Great Plains.
A tornado warning is a announcement that a tornado has been seen on weather radar.
A tornado watch is an announcement that tornadoes are possible in your area.
The safest place to be during a tornado is in the basement of a well built building.

5. Hurricane/Snow Hurricane Snow
A Hurricane is a tropical storm with winds higher than 119 kilometers per hour.
A hurricane begins over warm water as low-pressure area or tropical disturbance.
The center of the hurricane surrounds the eye.
A storm surge is a dome of water that sweeps across the coast where the hurricane lands.
A hurricane watch means a possible hurricane in 36 hours. A warning means 24 hours.
If you hear a hurricane warning, prepare to evacuate the area immediately.
Snow
Snow falls when humid air cools below 0 degrees Celsius
If you are caught in a snowstorm, try to find shelter from the wind.

6. Flooding What causes flooding?
Floods occur when so much water pours into a stream or river that it overflows its banks and covers the land on either side of the channel.
Unexpected floods are the most dangerous.
A flash flood is a sudden, violent flood that occurs within a few hours, or even minutes, after a storm.
Most flash floods bring a great deal of rain.
A dam breaking can also cause a flash flood.
How can dangers of floods be reduced?
Advance warning can reduce damage and save lives.
Weather satellites, rain gauges, and radar provide forecasts of flood heights at different points along a river.
A flood watch is the possibility of flooding.
A flood warning states that floods have already been reported or are about to occur.
The first rule of flood safety is to move to higher ground and stay away from floodwaters.
Floods also pose danger by knocking down power and electrical poles and cutting off power to people.
Floods can cause mudslides and landslides.
Floods can wash away roads.
Floods can wash into wells contaminating water supply.
People are told to boil water before using it if they are in a flood situation.

7. Predicting the Weather
How does technology help forecasters predict weather?
Meteorologists are scientists who study the weather and try to predict it.
Changes in technology have occurred in two areas: gathering weather data and using computers to make forecasts.
Cameras on weather satellites gather information.
Computers process this information for the forecasters to make predictions
Each forecast builds on the previous forecast.
Periodically a warm event like El Nino occurs. This contributes to rising surface temperatures in the Pacific Ocean.

8. Predicting the Weather.
What types of information are shown on the weather maps?
Fronts
Areas of low pressure
Types of Precipitation
Temperatures
Isobars
Isotherms.