> A high-pressure system is the result of the warm air > not being able to rise and so it pushes the cold air > in front of it making a warm front.
It's a bit different than that. Cold air drifts outward from the pole and settles downward as cold, dry, air, pushing outward. Warm, moist, air is pushed upward ahead of the advancing cold air. As the air rises, it condenses, which releases heat, and pulls the air up even farther, creating a low pressure area along the frontal boundary. Additionally, when the cold air pushes toward the jet-stream, such low pressure at the frontal boundary can be exagerated by the low pressure above, from the jet stream, creating a low pressure center which will follow the jet stream, trailing a cold front and a warm front outward from it. Craig Haynie (Houston)
