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.