This graphical prog has a wealth of meteorological information. The surface pressure is plotted for zero geopotential meters. This standardization allows pressures from high elevation regions to be compared with low elevation regions. Minimum pressure regions at zero geopotential meters are denoted as low pressures and maximum regions as high pressure. A low pressure that is less than 1000 millibars is very significant. High pressures tend to cover a large spatial area.
The precipitation is colorized on the panel in a variety of increments. This precipitation product represents general synoptic scale precipitation and general areal coverage by the different precipitation categories. It is not a good indicator of the exact amount of precipitation any one point will receive. Precipitation amounts are highly influenced by mesoscale and microscale processes. High precipitation maximums will be found in those regions with high upward vertical velocity coupled with high relative humidity through a deep layer.
The 1000 to 500 millibar thickness is shown in dashed lines with the exception of the 5100 thickness, 5400 thickness, and 5700 thickness shown as a solid line. The 5,100 thickness line generally separates Arctic air from Polar air. The 5,400 line is used as a general cutoff between rain and snow. The 5,700 geopotential meter thickness generally divides mid-latitude air from Tropical air. The thickness lines are in 60 geopotential meter increments. This prog is available on UNISYS weather at:
The combination of the zero geopotential meter surface pressure and thickness lines will show regions experiencing WAA and CAA. Lower thicknesses being advected toward a fixed location indicates CAA. Cold air has a lower thickness while warm air has a higher thickness (warm air expands and is less dense). Advection of higher thicknesses is indicative of low level WAA. Low level WAA leads to rising air on the synoptic scale. It is important to notice if the wind is flowing from a moisture source or a dry source. The wind direction near the surface crosses the isobars at about a 30-degree angle toward low pressure. WAA from a moisture source will generally cause more instability than WAA from a dry source because the combination of moisture and the dynamical rising caused by WAA can cause saturation of the air. This makes dynamically induced precipitation more likely.