Isobar - May 6, 1999

http://www.maine.gov/dep/air/meteorology/Windrosehome.html

Isobar lines on a map are lines of constant pressure.  Tracking these pressure differences are also an important part of weather forecasting.  Different pressure changes and magnitudes help denote different weather patterns, and hence, aid in the diagnosis and prediction of weather patterns.  The difference between subsequent isobars on a map will vary and depend upon the spatial distribution of surface data points you are able to obtain.

In the map shown above, isobar lines are plotted over the entire U.S.  From this map we are able to see that there are areas that attract immediate attention.  The low pressure system has a tight change (gradient) in the isobar lines and is associated with deteriorating weather conditions.  The high pressure system in the west doesn't have as tight of a gradient around it as the low pressure system and is associated with generally clear weather.  Fronts are depicted with darker lines and either triangles or half circles depending on the type of front that exists.