700 mb Heights and Dew Point Depressions
upper air data

Latest image

This panel shows the latest 700 mb field for geopotential height, winds, and dew point depression. 700 mb charts depict conditions in the middle troposphere (roughly 3000 meters). This is also referred to as the steering level, since most weather systems are "steered" by the winds at this level.

Geopotential height approximates the actual height of a pressure surface above mean sea-level and is represented by the solid white contours. The geopotential height field is given in meters with an interval of 30 meters between height lines. The locations of surface cyclones and anticyclones hold similar positions in the 700 mb geopotential height field.

Wind vectors indicate wind direction and wind speed and are drawn here as tiny white arrows. Wind vectors point towards the direction in which the wind is blowing and the longer the wind vector, the stronger the wind. The unit of magnitude for wind speed as depicted by the wind vectors is meters per second.

Dew point depression is represented by the color filled regions and the associated values are indicated by the color code located in the lower left corner of the forecast panel. Dew point depression is defined as the difference between the dew point temperature and the actual temperature. Regions of moist air are identified by smaller dew point depression values, while greater values indicate drier air. The greater the dew point depression (more negative), the more moist the air, which is precursor for the development of clouds and precipitation.

700 hghts, temps
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

850 hghts, temps