They are called anticyclones because the cold air in them flows outwards and clockwise, the opposite of a low. It is along the leading edge of these anticyclones that low-pressure waves sometimes develop; occasionally, one of these waves will intensify into a major storm. Why, and when, is still beyond the powers of science to predict. It typically happens over areas where a leg of the jet stream collides with subtropical air—the Great Lakes, the Gulf Stream off Hatteras, the southern Appalachians.
