This panel shows the most recent 850 mb fields for geopotential height, dew point depression and wind vectors. 850 mb charts depict conditions in the lower troposphere (roughly 1500 meters).
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 850 mb geopotential height field.
Wind vectors provide information about 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, a measure of relative humidity, 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 depressions are given as the difference between the dew point temperatures and the actual temperatures. The lower the dew point depression, the more moist the air, which is vital for the development of clouds and precipitation.
Advection of heat and moisture along the 850mb surface can be used to predict what will occur at the surface. Thermal advection can indicate forthcoming surface temperature changes, amplification of upper level troughs and ridges, and changes in pressure at the surface. Moisture advection is useful for predicting areas of precipitation.