Chapter 14 — AIR MASSES AND FRONTS 



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Figure 14-12. — Vertical cross section of a warm front. 



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Occluded Fronts 



An occluded front occurs when a cold front 

 overtakes a warm front. One of the two fronts 

 is lifted aloft, and the warm air between the 

 fronts is shut off from the earth's surface. 

 An occluded front is often referred to as an 

 occlusion. The type of occlusion is determined 

 by the temperature difference between the cold 

 air in advance of the warm front and the cold 

 air behind the cold front. 



WARM TYPE OCCLUSION. — If the air in 

 advance of the warm front is colder than the 

 air behind the cold front, the cold front rides 

 up the warm frontal slope. (See fig. 14-13.) 



COLD TYPE OCCLUSION. — If the cold air 

 ahead of the warm front is warmer than the 

 cold air behind the cold front, the cold frontal 

 surface underruns the warm front and the 

 occluded front is called a cold type occlusion. 

 (See fig. 14-14.) 



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