Their funnel shaped clouds rotate at velocities of up to 300 mile per hour and generally affect areas up to a mile wide and seldom more than 16 miles long. Four tornadoes have been sighted in King County since 1950. Snow storms or blizzards, which are snow storms accompanied by blowing wind or drifting snow, occur occasionally both in Washington State and King County. As exemplified in the Holiday Blast storm of 1996-1997, snow storms can also be associated with other natural hazards such as flooding and landslides given the right conditions. An ice storm can occur when rain falls out of warm moist upper layer of atmosphere into a dry layer with freezing or sub-freezing air near the ground.
Rain freezes on contact with the cold ground and accumulates on exposed surfaces.
Hail storms occur when freezing water in thunderstorm type clouds accumulate in layers around an icy core. Wind added to hail can batter crops, structures and transportation systems. The most recent severe storm to affect King County occurred over a multi-day period during the end of December 1996 and beginning of January 1997. This storm shows the potential hazards that can be associated with major storms both primary weather related hazards and secondary hazards including its impacts on infrastructure. This storm, referred to in the media as the Holiday Blast, was a series of three weather systems that included severe snow and ice followed by quick melting and runoff, causing flooding and landslides.