Isobars

Rather than use any old weather map of the US, I chose this one of Australia. This from a website that instructs one how to read weather maps and temperature formations shows a cold front moving in via a low pressure system over south-eastern Australia. The isobars, in that area show a decreasing pressure front which allows the cold air to descend. http://www.hsc.csu.edu.au/primary_ind/prim_ind_240/compulsory/RTE2503A/3264/reading_weather_maps.htm