Isotachs

http://www.crh.noaa.gov/iwx/?n=superoutbreak_meteorology

Isotachs are simply lines on a map that represent wind speed. Said lines intersect when wind speeds are the same. The map above shows the wind speed of the U.S. April 1974 from Arizona to the Great Lakes region. The red contour lines are the isotachs and the black contour lines represent height.