Skew-T log-P diagram

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Black and White Skew-T log-P
Color Skew-T log-P diagram. In this image, red lines are isotherms, solid green lines are the potential temperature, and dashed green lines are the equivalent potential temperature; these three all use the temperature scale at the horizontal 1000 mb level near the bottom. The blue lines are the isobars (scale on the left side) and the dashed purple lines are the saturated humidity mixing ratio (scale inside the graph, near the right).

A Skew-T Log-P diagram is one of four thermodynamic diagrams commonly used in weather analysis and forecasting. In 1947, N. Herlofson proposed a modification to the emagram which allows straight, horizontal isobars, and provides for a large angle between isotherms and dry adiabats, similar to that in the tephigram. It was thus more suitable for some of the newer analysis techniques being invented by the United States Air Force.

The major use for skew-T log-P diagrams is the plotting of radiosonde soundings, which give a vertical profile of the temperature and dew point temperature throughout the troposphere and lower stratosphere. The isopleths on the diagram can then be used to simplify many tedious calculations involved, which were previously performed by hand or not at all. Many skew-T log-P diagrams also include a vertical representation of the wind speed and direction using wind barbs. Important atmospheric characteristics such as saturation, atmospheric instability, and wind shear are critical in severe weather forecasting, by which skew-T log-P diagrams allow for quick visual analysis.

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