Weather
Fronts
Target #15- I can describe a weather
front
• 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
• 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
Target #17- I can differentiate between the
types of weather fronts that can form
• 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
• 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 fastmoving 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 midlatitude cyclone
Target #19- I
can state how
a mid-latitude
cyclone forms
Target #20- I
can describe
hurricanes
• 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 #21- I can summarize the impact a hurricane
induced storm surge has on the environment
• 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.
• 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
Target #23- I can
describe tornados
• Tornado: a destructive
rotating column of air
that has very high wind
speeds and that is
visible as a funnelshaped cloud
– Forms when a
thunderstorm meets
high-altitude winds
– The winds cause the
rising air to rotate
– Moves unpredictably
– Measured by the Fujita
Scale
Twister