Isobars

An isobar is a curve connecting values of equal pressure. On May 6, 1999, the wind blew hard across western South Dakota and portions of northeast Wyoming. The cause was the big "L" you see on the 12Z surface analysis above. Each isobar represents a 4mb pressure difference. Notice, there are five isobars over western South Dakota. There was a large 15mb pressure difference between the low and Rapid City.