How Does a Mid-Latitude Low Develop into a Storm System?
ES2003  Structure of a Mid-Latitude Storm System

The March 1993 "Storm of the Century" is a classic example of a mid-latitude low pressure cyclone. These systems begin as weak disturbances along the polar front, where cold polar air meets warmer air from the middle latitudes. As the air masses meet, the warmer air is pushed upward, creating a low pressure center at the surface. The surrounding surface air begins to spiral in toward the center of the low—counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

  !   Examine the diagrams of the map view (top) and side view (bottom) of a low pressure storm system. Try to visualize the system in three dimensions. Observe where different types of clouds and precipitation occur in relationship to the leading edges of the fronts.

Adapted from Peter J. Robinson and Ann Henderson-Sellers, 1999
Development of a typical low pressure storm system. The bottom diagram shows a side view along line A-B in the top diagram.

A cold front forms to the west of the low pressure center and a warm front forms to the east. The faster-moving cold front will eventually overtake the warm front, squeezing the warm air trapped between them upward and forming an occluded front. After a few days, the occluded front dissipates and the storm disappears.

1. On which side of the cold front are clouds and precipitation generally found?

2. On which side of the warm front are clouds and precipitation generally found?

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