Understanding pressure contour lines
isdirection and pressure distribution the surface chart can not be comprehended. Upper air charts are at a fixed pressure level, dewpoints and wind are reported from that pressure level. This is not true for the surface chart with the exception of pressure. Temperature, dewpoint and wind information are gathered from observation stations just a few feet above the surface for all elevations. Pressure, however, is normalized so pressures at high elevation stations can be measured against pressures at low elevation stations. All stations, no matter the elevation, are given the station pressure the site would have if it were at sea level. In a place such as New Orleans the surface pressure will be very close to the station pressure. But in a city like Denver, the station pressure may be 150 millibars less than surface pressure. Once Another huge difference between surface and upper air charts is the frontal