Weather Fronts and Systems

A cold front is when cold, almost always dry air moves towards the equator from the pole, these move much faster than warm fronts because they are denser than the preceding air mass, and so, instead of rising over top of it, cut underneath. Cold fronts often have a line of heavy rain right at their edge because they force the warm, often moist air up quickly, producing heavy rain. Cold fronts are narrow troughs of low pressure.

A warm front is the leading edge of a warm air mass moving toward the pole from the equator, advancing as the cooler air mass moves away, they represent wide troughs of low pressure and are often preceded by light rain because they are often followed by moist air, and if it moves faster than the air in front of it, it rises over it and the result is precipitation.

A low pressure system is a place were air rises and a high pressure system is were air falls. They both tend to create circular winds, clockwise for high pressure, and counter clockwise for low pressure, straight line winds occur in between a high pressure zone and a low pressure zone. These circular winds are because of the Coriolis affect, air wants to move from high pressure to low pressure, but because of the rotation of the earth, instead of flowing straight there is arcs around and flows into the low pressure as a spiral, this swerve is to the left, then back right in the northern hemisphere, and to the right and them back left in the southern hemisphere.

Fronts tend to move towards low pressure zones and away from high pressure zones, and in a clockwise direction, cold fronts approaching low pressure from the north and east, warm, mostly from the south and a little from the west. Along these fronts and a low pressure zones is were most "weather" happens, the bigger the temperature gradient and the moisture gradient between the air masses, the more sever the weather events are in general.

This (left) is a typical low pressure system, with warm air being lifted by the cold front, and rising in advance of the warm front, and both circleing, if the warm air is moist that will create clouds like this (right). As the fronts circle the low pressure zone, the cold front will move much more quickly than the warm front, and eventualy they will collide, forming an occluded front, were all of the warm air mass is lifted over the cold air mass.