On a given day, the surface pressures in various cities are given as: 1011 mbar Boston, MA 990 mbar Chicago, IL 998 mbar Detroit, MI 1009 mbar New York, NY The isobars are running approximately parallel to the lines of longitude (ie. north-south). Which way are the winds aloft blowing in Ann Arbor? All of the cities are roughly at the same latitude (north-south distance from the equator). From west to east (left to right on a map with north being up), the relevant cities are Chicago, Ann Arbor, Detroit, New York, Boston.