Extratropical

Extratropical refers to weather phenomena that form outside the tropics, primarily in the mid-latitudes between about 30° and 60° latitude. The term is most often applied to extratropical cyclones, large low-pressure systems that develop along or ahead of the polar front. These systems are driven by baroclinic processes—energy derived from horizontal temperature contrasts and jet stream dynamics—rather than the warm-core convection that powers tropical cyclones.

Extratropical cyclones typically feature sharp temperature gradients, frontal boundaries, and asymmetrical wind fields. They often organize around a low-pressure centre with cold and warm fronts extending from it. Precipitation is commonly associated with frontal bands and may include rain, snow, or a mix, depending on air masses. In high-latitude regions, these systems can bring strong winds, heavy precipitation, and coastal storm surge.

Compared with tropical cyclones, extratropical storms have a more asymmetrical structure and a cooler core. They rely on baroclinic instability rather than deep convection for development and can derive energy from the temperature contrast across the fronts. Some tropical cyclones undergo extratropical transition, losing their warm core and acquiring a broader, cold-core structure as they move poleward, often continuing as potent mid-latitude storms. Conversely, some extratropical cyclones form entirely in the mid-latitudes without tropical origins.

Geographically, extratropical cyclones are most common in the North Atlantic and North Pacific and can affect Europe, North America, and other mid-latitude regions. Hazards include strong winds, heavy precipitation, snow, blizzards, and rough seas.