Occluded Front
Anoccluded frontorocclusion( 4 ) usually forms around a low pressure system (Figure
16.20). The occlusion starts when a cold front catches up to a warm front. The air masses, in
order from front to back, are cold, warm, and then cold again. The boundary line, where the
two fronts meet, curves towards the pole because of the Coriolis effect. If the air mass that
arrives third is colder than either of the first two air masses, that air mass will slip beneath
the other two air masses. This is called a cold occlusion. If the air mass that arrives third
is warm, that air mass will ride over the other air mass. This is called a warm occlusion.
Figure 16.20: An occluded front with a warm front being advanced on by a cold front. The
order of air masses from front to rear is cold, warm, and then cold. ( 33 )
Occluded fronts can cause drying or storms. Precipitation and shifting winds are typical.
Theweatherisespeciallyfiercerightattheocclusion. ThePacificcoasthasfrequentoccluded
fronts. All of these fronts are part of the mid-latitude cyclone. These weather systems will
be discussed in the next lesson.
Lesson Summary
- An air mass takes on the temperature and humidity characteristics of the location
where it originates. Air masses meet at a front. - Stationary fronts become trapped in place and the weather they bring may last for
many days.