This happened while driving on a freeway. weather was sunny, in the 20s, pavement was dry but there were short icy patches under bridges. every time i passed over one of these patches i experienced severe fishtailing. i had to reduce speed to under 30mph to retain control of the car while traffic was passing me at 60+ mph. tires were new goodyear assurance. this is extremely nerve wracking and is a frequently reported problem on the subaru online user forums such as: http://www.ultimatesubaru.org/forum/topic/127473-ghost-walking/ the problem is not evident when driving on dry or on snowy roads.