LINES:

For this class of graphics, solid black lines represent isohypses which are defined as lines of constant geopotential height. In this case the geopotential height is for the 850 mb atmospheric pressure level (the 850 mb level is usually located around 1.6 km above the surface or 1 mile). The isohypses are drawn in thirty meter increments with the largest and smallest values also labeled. Thin blue lines represent lines of equal temperature called isotherms and are drawn and labeled in four degree Celsius increments. The intervals may be different depending on the product you are viewing therefore it is important to look at the line interval legend at the bottom right of the plot.

COLORS:

Background color represents the air temperature at 850 mb in degrees Celsius. The color-bar located at the bottom identifies the temperature for each shading of color. Thin blue lines separate regions of different temperature every four degrees.

WIND BARBS

Evenly spaced on the map are wind barbs that indicate the strength and direction of the wind at the 850 mb atmospheric pressure level.

1 kt ~ 1.15 mph ~ 1.85 km/hr

WHY IS THIS IMPORTANT?

The 850 mb atmospheric pressure level gives forecasters a good idea of the conditions in the lower atmosphere and how the surface air temperature will change during the daylight hours. These estimates are used for public and air quality forecasts. This product also depicts the horizontal transport of warm and cold air masses (i.e. advection). Regions of warm advection at 850 mb indicate upward motion, which favor cloud formation and possible precipitation. Finally, this graphic is also a critical component to determine snow/rain forecasts along with forecasting mountain conditions.