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Weather Fronts
When two air masses meet, the air within them does not easily mix. That is to say that the
air in one air mass will not easily mix with the air from another air mass. Instead, the air
stays within its own air mass. Because of this, a border forms between two clashing air
masses as they rub together. This border is called a front.
The term ‘front’ was first used by Norwegian scientists who compared two air masses
colliding to two armies as they clash on the battle front. Just like one army taking over
another in a battle, one air mass ultimately takes over, pushing the other one away.
Fronts should not be thought of as a vertical wall. This is because they are actually sloped,
like a hill. Often the slope of a front can be extremely gradual, taking hundreds of miles
across the surface of the Earth to reach an altitude of just one mile.
While the air in one air mass will not mix easily with the air from another air mass, along a
front there is some mixing. The front where air mixes is usually just a few miles or tens of
miles across.
Warm Fronts
Fronts that bring warm air are referred to as warm fronts. As this warm air approaches, it is
lifted upward above the cooler air. As the air in the warm air mass rises it expands, causing
it to cool down. As it cools, water vapor can condense, creating precipitation.
This precipitation is generally light and forms gradually. Clouds first form in the sky as the
warm air is lifted upward, proceeded by thicker clouds, and ultimately some form of
precipitation.
Cold Fronts
A front bringing in a cold air mass is referred to as a cold front. Because cold fronts move
along the ground where they encounter friction, they move slower at ground level than they
do further up in the atmosphere. For this reason, cold fronts tend to be more sloped than
warm fronts.
Typically cold fronts move faster than their warmer counterparts. The combination of higher
speed and slope push warm air masses upward very quickly. This quick upward air
movement causes the warm air being displaced to cool quickly, becoming turbulent. This
turbulence often can be the cause of extremely violent weather.
Because cold fronts move quickly, the weather associated with them typically also moves
quickly and passes over a particular location in a short period of time. The turbulent weather
generally stays right in line with the front.
Stationary Front
When two air masses come together but neither displaces the other, the boundary between
them is referred to as a stationary front. It is difficult for meteorologists to predict the weather
along a stationary front, though it often resembles that of a warm front.
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