Transcript Weather Systems

Weather Systems
Pressure Systems
• Air wants to move from areas of high pressure to
areas of low pressure
• Low pressure system: the air has a lower pressure
than the surrounding air
Low Pressure Systems
• Air moves in and pushes way air
that was there
• The air rises, water vapor
condenses into clouds
• Low pressure systems bring cloudy
weather and storms are likely
High Pressure System
• High Pressure Systems: the air has a higher
pressure than the surrounding air
• Remember: Air always wants to move from a high
pressure to a low pressure!
High Pressure Systems
• Air leaves a high pressure
system and leaves a “hole” to
be filled
• As the air sinks, water
evaporates becoming water
vapor
• High pressure systems bring
good weather and clear skies
Pressure Systems
Low Pressure
High Pressure
Weather Fronts
• Weather front: an area where two air masses with
different temperatures and densities collide but do
not mix
• The collisions often cause storms and changing
weather
Warm Front
• Warm front: when a warm air mass is pushing into
a cold air mass
• As a warm front approaches, the temperature and
air pressure drop
• Warm fronts move slowly and bring clouds and
rainstorms
Cold Fronts
• Cold Front: when a cold air mass is pushing into a
warm air mass
• Cold fronts move fast and produce dramatic
changes in weather
Cold Fronts
• As the cold front passes, the winds become gusty,
and the temperature drops rapidly
• Cold fronts bring heavy rain, snow, hail,
thunderstorms and cooler weather
Stationary Fronts
• Stationary Front: when a warm air mass and a cold
air mass push against each other but neither one
can move the other
Stationary Front
• A stationary front may stay for
days over an area
• When the wind direction changes,
the front will break apart
• During a stationary front, weather
is cloudy and rain or snow often
falls
Occluded Fronts
• Occluded Front: when a warm air mass and a cold
air mass push into each other and the cold air mass
overtakes the warm air mass
Occluded Front
• Occluded fronts form around low pressure systems
• Occluded fronts cause changes in temperature and
wind direction
Severe Weather
• Thunderstorms: rain, hail, wind and lightning
• Thunderstorms form when air rapidly rises in a low
pressure system
Thunderstorms
• Lightning: small ice crystals that are positively
charged collide with ice crystals that are negatively
charged
• Thunderstorms are measured on a scale of 1 to 5, 5
is very severe
Severe Weather
• Hurricane: a storm with violent wind exceeding 74
mph
• Hurricanes are measured on a scale of category 1
to category 5
• Category 5 is catastrophic
Severe Weather
• Tropical Storm: an intense low pressure wind
system with hurricane force winds that forms in
topical areas
• Cyclone: a tropical storm in a low pressure region
surrounded by thunderstorms that produce heavy
rain and strong winds
Severe Weather
• Tornado: a mobile, destructive vortex of violently
rotating winds
• Tornadoes are measured on a scale from F1 to F5,
F5 tornadoes are the most destructive
Severe Weather
• Blizzard: a severe snow storm with strong winds
and heavy snowfall
• Drought: an extended period of time when a region
does not get rain
Severe Weather
• Flash flood: rapid flooding caused by heavy rainfall
or rapid snow melt
• The ground is too frozen, too saturated or too dry
to soak up the water fast enough
Severe Weather
• Monsoon Wind: a change in the direction and
strength of the wind
• Caused by: abnormal heating of the surface of earth
• Monsoon rains: a rainy season that can last for
weeks or months
• caused by a change in wind direction
Severe Weather
• El Niño: the abnormal warming of Pacific ocean
currents
• Causes droughts in Asia and flooding in the Americas
La Niña
• La Niña: the abnormal cooling of Pacific ocean
currents
• Causes flooding in Asia and droughts in the Americas