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Weather
Fronts
• When two unlike air masses meet, density difference usually keep the air masses separate.– Cool air masses are denser than warm air
masses– Their interaction is called a front• Can be several hundred to several thousand
kilometers long• Initiates weather activity
Target #15- I can describe a weather front
• For a front to form one air mass must collide with another air mass–Kind of front determined by how the masses move in relationship to each other
Target #16- I can state how a front
forms
• Cold Front: occurs when a cold air mass overtakes a warm air mass–The cold air lifts the warm air mass• If the warm air is moist, clouds will form
–The faster the front moves the stronger the storms• Squall line: where thunderstorms form
along a fast moving cold front
Target #17- I can differentiate between the types of weather fronts that can
form
• Warm Front: occurs when a warm air mass overtakes a cold air mass–Less dense warm air
rises over the cooler air–Generally produces
precipitation over a large area–May cause violent
weather
• Stationary Front: occurs when two air masses meet, but neither displaces the other– Either moves slowly or
not at all–Weather produced is
similar to a warm front
• Occluded Front: occurs when a fast-moving cold front overtakes a warm front and lifts the warm air off the ground completely– Usually results in rain storms
• Mid-latitude cyclones–A wave forms at the boundary where
cold polar air meets tropical air• Usually occurs in the mid-latutides (half way
between the equator and the poles)– Hurricanes: Over oceans– Tornadoes: Over land
• Illustrated by a counter-clockwise rotation of air
Target #18- I can describe
a mid-latitude cyclone
Target #19- I can state how a mid-
latitude cyclone forms
• Hurricane– a tropical storm that
forms over a warm ocean
– has strong wind speeds of more than 120 km/h • spirals toward its intense
low pressure center
–Begins when warm, moist air over the ocean rises rapidly• Winds increase toward the
center (the eye)
– Causes a storm surge rising sea level
Target #20- I can describe hurricanes
• Storm surges are frequently the most devastating element of a hurricane.– As a hurricane’s winds spiral around and around
the storm, they push water into a mound at the storm’s center.• This mound of water becomes dangerous when the
storm reaches land because it causes flooding along the coast.
• The water piles up, unable to escape anywhere but on land as the storm carries it landward.
– A hurricane will cause more storm surge in areas where the ocean floor slopes gradually. This causes major flooding.
Target #21- I can summarize the impact a hurricane induced storm surge has on the
environment
• Safir-Simpson Scale: a 5 category scale that groups hurricanes into groups by pressure, wind speed, and storm surge
Target #22- I can identify what scale is
used to measure the strength of a
hurricane
• Tornado: a destructive rotating column of air that has very high wind speeds and that is visible as a funnel-shaped cloud– Forms when a
thunderstorm meets high-altitude winds
– The winds cause the rising air to rotate
–Moves unpredictably–Measured by the Fujita
Scale
Target #23- I can describe
tornados
Twister
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