The transition zones between two separate air masses, called frontal or baroclinic zones, are divided into fronts.
Fronts are as large as real weather systems, and can be several thousand kilometres long and wide.
They move at different speeds, since each air mass pushes them along at its own rate. 8.1 Classification Four of the six types of air masses that surround the Earth influence the weather in North America. Depending on the season, then, meteorologists daily deal with up to four types of baroclinic zones, with strong thermal and moisture gradients. Generally speaking, each of these zones is identified according to the colder air mass, which is almost always on the north side. An arctic front separates a continental arctic air mass from a maritime arctic air mass, to the south.