Surface weather analysis United States, temperature and dewpoint are plotted in degrees Celsius. The wind barb points in the direction from which the wind is coming. Each full flag on the wind barb represents of wind, each half flag represents . When winds reach , a filled in triangle is used for each of wind. In the United States, rainfall plotted in the corner of the station model are in inches. The international standard rainfall measurement unit is the millimeter. Once a map has a field of station models plotted, the analyzing isobars (lines of equal pressure), isallobars (lines of equal pressure change),
Atmospheric pressure Siberian High often attains a "sea-level pressure" above , with record highs close to . The lowest measurable "sea-level pressure" is found at the centers of tropical cyclones and tornadoes, with a record low of (see Atmospheric pressure records). "Surface pressure" is the atmospheric pressure at a location on Earth's surface (terrain and oceans). It is directly proportional to the mass of air over that location. For numerical reasons, atmospheric models such as general circulation models (GCMs) usually predict the nondimensional "logarithm of surface pressure". The average value of surface pressure on Earth is 985hPa. This is in contrast to