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FRONTS
Understanding & Predicting Weather
Air Mass
4 Types of Air Masses
Air Mass | Symbol | Formed Over | Weather |
Continental Tropical | cT | Warm Land | Warm & Dry |
Continental Polar | cP | Cold Land | Cold & Dry |
Maritime Tropical | mT | Warm Water | Warm & Wet |
Maritime Polar | mP | Cold Water | Cold & Wet |
CFU
Arizona and Arkansas are both at the same latitude. Why does Arizona experience such different amounts of rainfall?
Cold Front-
The leading edge of a mass of cold air. Arrows indicate direction.
Warm Front-
Leading edge of a mass of warm air. Semicircles indicate direction.
Stationary Front-
A cold or warm front that stops moving.
Occluded Front-
When a cold front overtakes a warm front.
Precipitation
Copyright © 2007 by Interactive Science Teacher™
Friday December 11, 2009 10:09am
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Cold Front-
The leading edge of a mass of cold air. Arrows indicate direction.
Warm Front-
Leading edge of a mass of warm air. Semicircles indicate direction.
Stationary Front-
A cold or warm front that stops moving.
Occluded Front-
When a cold front overtakes a warm front.
Precipitation
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Copyright © 2007 by Interactive Science Teacher™
Understanding The Weather
Remember that the type of ocean surface current that passes by has a direct effect on the climate and weather of the land nearby.
Warm surface currents bring warmer, moister air to the surrounding areas.
But cool surface currents bring cooler, drier air to the surrounding areas.
The Gulf Stream
The Alaska Current
The California Current
Cities in these areas enjoy the same, stable climate throughout the year. The ocean helps keep everything stable and unchanging.
These are called maritime climates…they rarely experience big, dramatic changes.
Miami, New Orleans, Houston, Seattle, San Francisco, and San Diego are examples…what do you know about these climates?
However, the farther you get away from the coast, the more dramatic your weather changes throughout the year.
These are called continental climates. Summers can be very hot and winters can be very cold. Rainfall can vary tremendously.
Pittsburgh, Memphis, Minneapolis, Denver, Oklahoma City and Dallas are examples…what do you know about summer and winter in these climates?
Let’s start looking at the weather. On any weather forecast, you are going to see areas of Low Pressure.
Low pressure areas form when warmer air begins to rise high up into the atmosphere….like a hot air balloon.
As the warm air rises, it swirls counterclockwise and pulls moist, humid air up with it.
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These low pressure areas suck air up and bring warmer and wetter weather wherever they go.
They are usually associated with bad weather. This is some really warm and humid air. As it rises higher and higher, it starts to cool…
…and form clouds and precipitation.
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On any weather forecast, you are also going to see areas of High Pressure.
High pressure areas form when cooler, denser air begins to sink back down to the Earth….like a leaf blower.
As the cool air sinks, it swirls clockwise and blasts cool, dry air back down on the ground.
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These high pressure areas usually bring dry and sunny weather with them.
They are usually associated with great weather. This is really dry, cool air. And no moisture means…
…no clouds or rain. Just beautiful sunny days!
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Pressure systems usually deal with the amount of moisture in the air, though. Big, dramatic changes in the air temperature come from moving fronts.
A front is the boundary, or dividing line between two different types of air. Warm Fronts generally move from the South to the North and bring warmer, humid air with them.
The direction the half circles are pointing tells you which direction the front is moving.
As the front moves through, it drags the associated weather with it into the area.
Cold Fronts generally move from the North to the South and bring cooler, drier air with them.
The direction the triangles are pointing tells you which direction the front is moving.
If there is enough humidity in the air (evaporated water), you will usually experience some rain and storms as the fronts move through the area.
Colder temperatures cause evaporated water in the air to condense into liquid water.
This can cause rain and storms as the cold front moves in.
Now let’s look at some special weather situations.
Rain Shadows are dry areas of land that receive little rainfall on one side of mountains…
…while the side of the mountains closest to the ocean are drenched in rain.
The moist, humid air coming off the ocean just can’t make it over the tall mountains. So it constantly pours on one side and stays dry on the other.
Phoenix and Seattle are good examples. What do we know about the rainfall in these places?
Now let’s look at another special weather situation.
Hurricanes are massively huge low pressure systems that develop throughout the summer and fall in the warm tropical waters.
As it comes on land, the system dumps a ton of rain, often flooding the area.
The specific heat of the water allows it to heat up slowly and gain a lot of energy.
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So how does all of this affect us here in Tejas?
During the summer and fall, warm humid air from the Gulf Of Mexico streams up from the South.
But, its usually so hot around here that it is not cool enough for the humidity in the air to condense into rain. So we stay hot and dry…but miserably humid.
What about those crazy Texas winters?
During the spring and winter, cold fronts from the North and West provide the chilly temperatures needed to condense our humid air.
So we end up with a lot more rain…and sometimes ice and snow.
Let’s Review….
What is the name of the warm water current that keeps the Southeastern United States warm and muggy throughout the year?
The Gulf Stream
How are Rain Shadows formed?
The moist, humid air coming off the ocean just can’t make it over the tall mountains. So it constantly pours on one side and stays dry on the other.
Let’s Review….
How are Low Pressure systems different from High Pressure systems?
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Let’s Review….
How are Cold Fronts different from Warm Fronts?
Click here to get the current weather outlook for the United States.
Special Weather Fronts
Occluded & Stationary Fronts
Occluded Front
Stationary Front
Stationary = Stay still
CFU
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