These charts are prepared twice a day at 0000Z and 1200Z for several mandatory pressure levels (925 mb, 850 mb, 700 mb, etc.) from the temperature, humidity, and wind data provided by the ...

For example, the solid lines on the constant pressure chart below depict the height of the 500 mb surface. So, why use constant pressure instead of “constant altitude” to depict the weather aloft?

As an example of how to use this chart, if your car runs 12.00/114 mph at a 3,000-foot-altitude track, use the correction factors (e.t. x 0.9640 and mph x 1.0381) to generate altitude-corrected ...