The Polar Front Theory of Cyclogenesis was developed in the early 1900s to explain the formation of mid-latitude cyclones. But what is a mid-latitude cyclone and why is it important? A mid-latitude cyclone is a large-scale low pressure system that travels eastward around the planet between 30 and 70 degrees latitude. It is crucial to day-to-day weather changes and to bringing rain and storms to much of the planet. The polar front is the boundary between the cold winds from the poles and the warm winds from closer to the equator. The cold winds blow from the east between 60 and 90 degrees latitude and are called the polar easterlies. The warm winds blow from the west between 60 and 30 degrees latitude and are called the westerlies. These winds cause mid-latitude cyclones.