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