AIR MASSES A large body of air (thousands of miles) Changes in weather are caused by movements of air masses As an air mass moves away, temp & humidity change.

Classification Air masses are named from the area where they come from. Classified according to : temperature & moisture content.

Tropical- HOT air mass formed in tropics Polar- COLD air mass formed near poles Maritime- air mass formed over oceans, WET Continental- air mass formed over land, DRY

TYPES OF AIR MASSES 1.MARITIME TROPICAL 2.MARITIME POLAR 3.CONTINENTAL POLAR 4.CONTINENTAL TROPICAL

Warm, humid air mass formed over ocean near equator. Summer = hot humid weather Winter = heavy rain/snowfall

Cool, humid air masses formed over ocean near poles Summer = cool temps, fog, rain Winter = snow, cold temps

Hot, dry air masses formed mostly in the summer over dry lands of SW & N Mexico.

Large, cold air mass formed over land in Canada & Alaska. Winter- extremely cold, dry air. Summer- cold, dry air temps

Prevailing Westerlies push air masses west to east. Jet Stream- blow west to east Fronts- boundaries between air masses, changeable weather & storms develop along fronts.

Colliding air masses can form 4 types of fronts: 1. Cold fronts 2. Warm fronts 3. Stationary fronts 4. Occluded fronts

forms when a cold air mass meets & pushes under a warm air mass. Warm air cools, clouds form, & heavy rain. (thunderstorms). cool weather

Forms when a warm air mass moves over a cold air mass. Rain showers then hot, humid weather.

Warm air mass meets a cold air mass & no movement occurs. Produces rain & clouds.

When a warm air mass is caught between 2 colder air masses. Warm air cut off. Produces clouds, rain/snow.

A center of low air pressure, winds spiral inward. As air rises in a cyclone, the air cools forming clouds & precipitation.

High pressure areas of dry air where winds spiral outward. (clockwise) Descending air in an anticyclone causes dry, clear weather.

STORM A violent disturbance in the atmosphere

A small storm often accompanied with heavy precipitation & thunder & lightning. Form in large cumulonimbus clouds called thunderheads.

On hot, humid days, warm air rises rapidly, & cools forming cumulonimbus clouds. This movement of air creates updraft & downdraft winds.

Areas of (+)/(-) charges build up in storm clouds. It is a sudden discharge of electricity between 2 clouds or the cloud and the ground. Electric energy is released.

Light travels faster than sound. Lightning heats air. Heated air expands rapidly which results in sound waves (thunder).

T-Storm Damage Heavy rains which can lead to floods. Lightning, Hail, & winds can cause damage.

Whirling, funnel shaped cloud that reaches down from a storm cloud to touch earth’s surface. Warmth & Moisture feed it Season: late spring/early summer

Warm, humid air meets cold, dry air. A squall line of thunderstorms develop which can develop into a tornado. Warm air rises rapidly & begins to rotate. The cloud will then start to descend to earth in a funnel.

Tornado Alley- Mid-West US This is where the conditions are the best- warm, humid air from Mexico mixes with cold, dry air from Canada.

Tornadoes occur most frequently in the US Damage comes from strong winds & flying debris.

Tornadoes are ranked on the Fujita Scale (by the amount of damage they cause.) F0 light damage to F5 extreme damage. F4 F5 tornadoes account for only 1% of all tornadoes.

A tropical cyclone that has winds of 119kmh or higher. Forms in the Atlantic, Pacific, & Indian Oceans. In western Pacific- typhoons.

HURRICANE FORMATION It begins over warm ocean water as a low-pressure area (tropical disturbance). It grows from a disturbance to a tropical storm and maybe to a hurricane.

It draws energy from warm, humid air at ocean’s surface. Warm air rises to form clouds, more air is drawn into the system. Storms bands, high winds, & heavy rains spiral around a center.

Cool, dry air sinks into the center (eye) of the hurricane. Hurricanes last longer than other storms- usually a week or longer.

Year round, most precipitation begins in the clouds as snow.

Cold, dry air moves across warmer water picking up water vapor & heat from the water. Once the air reaches the other side of the lake, air condenses & falls as snow.

In New York, Buffalo & Rochester are 2 of the snowiest cities in the US because of Lake-Effect Snow.

Snowstorm Safety Find shelter from the wind. It can be dangerous because high winds/snow limit your vision so you can get lost easily & you can lose a lot of body heat out in the cold.

Meteorologists Scientists who study the causes of weather & try to predict it. Meteorologists use maps, charts, & computers to analyze weather & prepare weather forecasts.

Lines joining places that have the same temps.

Lines joining areas with the same air pressure.

TECHNOLOGY Has improved the accuracy of weather forecasts. Weather balloons carry instruments into the troposphere & stratosphere to measure temp., air pressure, & humidity.

Weather Satellites- orbit earth in the thermosphere, cameras make images of the earth’s surface, clouds, & storms which get sent to meteorologists to analyze.

Computer Forecasts- gathers weather data from a large area then the computer works through thousands of calculations using equations from weather models to make forecasts for 12, 24, & 36 hours. Each one builds on the previous forecasts.