Download - Weather patterns
Weather Patterns
Weather Patterns
• Constant movement of air and moisture change the atmosphere
• This is related to the development and movement of air masses– Air Mass: large body of air with the same
properties as the surface it develops over
Air Masses
• Where the air mass develops will give it it’s characteristics.
• Over water, the air will be moist and over land it will be dry
Pressure Systems
• Molecules push down from above, creating atmospheric pressure
Pressure Systems
– Variation in atmospheric pressure determines the weather
• Areas of high pressure = descending colder air– Sinking high pressure air makes it more difficult for
air to rise and clouds to form– High pressure = good weather– Low pressure = clouds
Pressure Systems
Fronts• Front: a boundary
between two different air masses– Storms and precipitation
occur here– Air in a front will move
from high pressure to low pressure
• When two air masses with different characterizations meet, they do not blend
When Air Masses Have Different Characteristics
• The cold air mass will move under the warm air mass and the warm air will rise and winds begin
• Winds blow from high pressured air to low pressured air
Four Types Of Fronts
• Warm– Develop when a less dense warm air mass slides over departing cold air
mass• Cold
– Cold air mass moves under a warm air mass and pushes it along a steep front
– Move at twice the speed of a warm front– Creates a narrow band of violent storms
• Occluded– Result of two cool air masses merging, and forcing warm air between
them to rise– May cause strong winds and heavy precipitation
• Stationary– Pressure differences cause a warm or cold front to stop moving
• May stay in the same place for several days• Causes light wind and precipitation
Severe Weather
• These types of weather pose a danger to people and animals– They include:
• Blizzards• Thunderstorms• Tornadoes• Hurricanes
A Thunderstorm• Air speed can reach 89km per hour• Occurs inside warm moist air
masses and at fronts• Downdrafts-
– Raindrops collide with other droplets and grow larger
– Heavy raindrops fall, dragging down air
– This causes downdrafts, which make strong winds
– Lightning • Rapid uplift of air builds
electric charge in clouds• Currents of opposite electric
charge flowing in between regions makes lightning flash
• Can leap cloud to cloud or cloud to earth
– Thunder• Lightning rapidly heats air
around it, the air expands and molecules crash into eachother
– Can reach 5x the temperature of the surface of the sun
Tornadoes• Tornado – violent, whirling wind,
which moves in a narrow path over land.
• Wind shear- difference in wind direction and speed– Strong updraft will tilt wind shear and
produce rotation inside• Funnel cloud will appear• Can go up to 500km per hour• Most occur in United States
Hurricane
• Most powerful storm• Hurricane – large, swirling, low
pressure system that forms over tropical oceans– Turns heat energy in ocean into wind
• Must be 120km per hour to be classified as hurricane
• Similar to low pressure systems on land but stronger
Section Wrap Up
1) Why do high pressure areas usually have clear skies?
2) Explain how a tornado develops from a thunder storm.
3) How do two fronts form at a low pressure area? Which would bring the most severe weather?