What defines an extratropical cyclone?

An extratropical cyclone is defined as a cyclonic scale storm that is not classified as a tropical cyclone. These systems typically form at higher latitudes and are associated with fronts and large-scale circulation patterns in the atmosphere. Unlike tropical cyclones, which derive their energy primarily from warm ocean water and are usually found in tropical regions, extratropical cyclones can develop over land or water and are influenced by temperature contrasts between air masses.

The key characteristics that distinguish extratropical cyclones include their association with the mid-latitude jet stream, their formation due to temperature gradients, and their propensity to bring varying weather patterns including rain, snow, and strong winds. This makes them pivotal for understanding weather systems in temperate regions.

The other options discuss characteristics that do not apply to extratropical cyclones. A storm that only occurs in tropical regions would refer to a tropical cyclone, which is distinctly different. Similarly, a storm formed specifically from warm ocean air is a hallmark of tropical cyclones rather than extratropical ones. Lastly, weather phenomena occurring in low latitudes typically relate to tropical systems, whereas extratropical cyclones are more common in the higher latitude regions of the Earth.