Isobar

A line on a weather chart joining places with the same atmospheric pressure at a stated time.

Surface synoptic charts normally plot isobars at regular pressure intervals, commonly measured in hectopascals. Their pattern shows the position and shape of pressure systems and troughs and helps reveal the pressure gradient across an area.

Closely spaced isobars indicate a stronger pressure gradient than widely spaced isobars and are often associated with stronger winds, but wind direction and speed are also affected by latitude, friction, curvature and local conditions. An isobar is not a track showing where a weather system will move.