This document discusses the stages of depression formation. It begins with a warm air mass meeting a cold air mass, forming a depression. In the second stage, rain occurs along the warm and cold fronts as air rises and cools. Finally, the cold front catches up to the slower warm front, forming an occluded front where the three air masses converge.

1. Depressions John Harris - Head of Geography - Radley College - UK [email_address] http://geography.radley.org.uk

2. Depressions form where a warm air mass eg Tropical Maritime meets a cold air mass eg Polar Maritime Depression stage 1

3. Depression stage 2 : maturity Rain often occurs along the warm and cold fronts where air rises, expands, cools and condenses

4. Warm front

5. Cold front

6. Depression - cross section

7. Depression stage 3 : occlusion The cold front eventually catches up the slower moving warm front to form an occluded front.

8. Occluded front - cross-section