Non-classic extratropical cyclones on Met Office sea-level pressure charts: Double cold and warm fronts

Four cool seasons of Met Office sea‐level pressure analyses revealed 217 extratropical cyclones (<995hPa): 94 had single warm and cold fronts (Norwegian cyclones) and 123 had two cold fronts, two warm fronts, or both two cold and two warm fronts. The most common double‐front cyclone developed when warm and cold fronts were drawn into the circulation of a growing cyclone to produce a cyclone with two cold and two warm fronts. Thus, double‐front cyclones, representing non‐classic cyclone evolutions, are more common than single‐front cyclones in the real atmosphere, and forecasters and scientists should be aware of their existence.