Dear Tom,
Weather systems move generally from west to east, faster than the speed of the Earth. Why?
Mark Jaros, Pleasant Prairie, Wisconsin

Dear Mark,
It is certainly correct that a general west-to-east movement of weather systems prevails across the United States and most of Canada. These winds are known as the “prevailing westerlies”. However, not all of the prevailing atmospheric motions behave in that manner. Two zones of generally east-to-west moving weather systems  prevail in the Northern Hemisphere, one to the north and the other to the south of the mid-latitude prevailing westerlies.

The same circulation pattern exists in the Southern Hemisphere.

To the south of the zone of prevailing westerlies in the Northern Hemisphere lies an area called the Northeast Trades. It extends from about southern Florida all the way to the Equator. Prevailing winds to the south of the Equator are labeled the Southeast Tradewinds.

To the north of the zone of prevailing westerlies and close to the North Pole lies a zone called the Polar Easterlies.

The pattern of prevailing winds in the Southern Hemisphere is identical to prevailing wind circulation in the Northern Hemisphere.