Because air and moisture move in the atmosphere, weather constantly changes.
Air mass –large body of air with properties like the part of Earth’s surface over which it is formed.
Highs and Lows <ul><li>Stormy weather is associated with low pressure areas. </li></ul>
<ul><li>Fair weather is associated with high pressure areas. </li></ul>
<ul><li>Air pressure is measured by a barometer. </li></ul>
Front –a boundary between two different air masses.
Clouds, precipitation, and storms occur at frontal boundaries.
Cold front- where colder air advances under warm air.
Warm front –where warmer air advances over colder air
Occluded front –involves three air masses of different temperatures.
Stationary front –air mass and their boundaries stop advancing. <ul><li>Warm, moist air is forced rapidly upward, where it cools and condenses. </li></ul><ul><li>Strong updrafts of warm air and sinking, rain-cooled air cause strong winds. </li></ul>
Thunderstorms occur inside warm, moist air masses and fronts.
Lightning <ul><li>Movement of air inside a storm cloud causes parts of the cloud to become oppositely charged. </li></ul><ul><li>Current flows between the regions of opposite electrical charge, forming a lighting bolt. </li></ul>
Thunder –lighting superheats the air, causing it to expand rapidly and then contract, forming sound waves.
Tornado –a violent, whirling wind that moves in a narrow path over land.
Hurricane –a large, swirling, low-pressure system that forms over tropical oceans .
Blizzard – a winter snow storm with strong winds, cold temperatures, and low visibility, that lasts more than three hours.
Severe Weather Safety <ul><li>A National Weather Service watch means conditions are favorable for severe weather to develop. </li></ul><ul><li>A warning means that severe weather conditions already exist. </li></ul>
The National Weather Service makes weather maps.
Station models show weather conditions at a specific location.
Temperature and Pressure <ul><li>Isotherms are lines on a weather map connecting points of equal temperature. </li></ul><ul><li>Isobars are lines on a weather map that connect points of equal atmospheric pressure. </li></ul>
Weather fronts move from west to east. <ul><li>THIS IS DUE TO THE SPIN OF THE EARTH AND THE GLOBAL “PREVAILING WESTERLY WINDS” </li></ul>