How do fronts change
Although the lines
on a weather chart show the position of the front at the earth's surface,
fronts do not simply rise vertically into the atmosphere their position
changes with altitude. This is due to the fact that hot air rises. As
the warm air mass moves in on the cold air mass, the warmer air glides
easily over the top of the cooler air. This results in the warm front
extending further forward the higher up you go. So the warm front passes
overhead at altitude before it passes at surface level.
is in contrast to a cold front where the front passes over at ground level
first. Because the colder air pushes under the warmer air mass, this cold
front lags behind at higher altitude.
How fronts affect the weather