Environmental computer systems, such as TESS,have built in programs that will plot a complete upper-air observation report on a background representative ofthe Skew T, Log P and calculate many values routinelyfound by using the diagram. However, the computerplot does not provide the overall detail provided by apaper copy of the Skew T chart. An actual DOD-WPC9-16 Skew T, Log P Diagram should be available atyour command.Detailed information on plotting, analysis, andforecasting techniques using the Skew T, Log Pdiagram is contained in NAVAIR 50-lP-5, The Use ofthe Skew T, Log P Diagram in Analysis andForecasting.DIAGRAM FAMILIARIZATIONThe Skew T, Log P diagram is a set of curved andstraight lines that graphically represent the physicalprocesses that occur in the atmosphere as moist air risesand descends. In the upper-right comer of each diagramis a detailed explanation of each set of lines on thediagram. The Skew T, Log P diagram is printed inblack, pastel green, and light brown. DOD WPC(Department of Defense, Weather Plotting Chart) 9-16is the basic chart. Several different variations of thechart are available and listed in the NIMA Catalog. Allversions have the basic plotting scales discussed below,superimposed over each other (fig. 4-24). These scalesare used as guides for plotting observed information,and then for deriving other values when analyzing theplotted information. The use of the Skew T, Log Pdiagram allows analysts to find important values andindicators without having to preform complexthermodynamic calculations.Isobar ScaleIsobars are lines of equal pressure. The scale is aseries of horizontal, solid brown lines spacedlogarithmically at 10-hectopascal intervals from 1050Figure 4-24.—A portion of a Skew T, Log P diagram (version 9-16-1) showing the superimposed plotting scales.4-25