 This theory still retains merit, as it is a good description for extratropical cyclones over continental landmasses.A second competing theory for extratropical cyclone development over the oceans is the Shapiro-Keyser model, developed in 1990.Its main differences with the Norwegian Cyclone Model are the fracture of the cold front, treating warm-type occlusions and warm fronts as the same, and allowing the cold front to progress through the warm sector perpendicular to the warm front.