Extratropical cyclones (also called lows or depressions) are the dominant weather systems in mid-latitudes (30°–60°). They form along the polar front where warm tropical and cold polar air masses interact, creating systems with warm, cold, and occluded fronts.
Life cycle
Following the Bergen model, they progress through frontal wave, development, maturity, and occlusion stages. Unlike hurricanes, they derive energy from horizontal temperature contrast (baroclinic energy), not ocean heat. They can reach 2,000–3,000 km in diameter and hurricane-force winds in cases of explosive cyclogenesis.