Winter storms differ from tropical storms not only in terms of their areas of formation and tracks, but above all in their intensity and geographical extent. They form in the transition zone between subtropical and polar climate zones. When outbreaks of cold polar air meet subtropical warm air masses, extensive low-pressure vortices are generated. The storm intensity peaks in late autumn and winter, when oceans are still warm but the polar air is already cold – hence the designation winter storm. Maximum wind speeds are 140–200km/h, although speeds far in excess of 250 km/h are possible in exposed coastal locations and on higher mountains. The wind fields can be as much as 2,000km wide.
Ice and snowstorms (blizzards) are other types of extratropical storm. As with other extratropical storms, which mainly inflict damage through high wind speeds, losses from blizzards can reach tens of billions of euros and are caused by ice or snow pressure. Severe blizzards on the north-east coast of the US and Canada, where they are referred to as “nor’easters”, can be particularly costly.