# Skew-T
A Skew-T diagram, also known as a sounding, is plotted from data measured by weather balloons. National Weather Service observation sites usually release weather balloons twice a day. When the weather is expected to be severe, some sites may release them more often. The data plotted on the Skew-T chart includes temperature, dew point, and winds at various levels in the atmosphere.
Skew-T charts can be used to forecast a wide variety of phenomena, including thunderstorms, hail, heavy rainfall, or tornadoes. During the winter, Skew-T charts are useful for determining the type of likely precipitation, whether it's snow, sleet, or freezing rain.
[This web page](https://medium.com/@WeatherDecTech/part-1-have-you-heard-of-a-skew-t-diagram-and-do-you-know-what-they-are-used-for-5e4033b70681) provides a basic overview of Skew-T charts. For more in-depth information, see the [Skew-T tutorials at weather.gov](https://www.weather.gov/source/zhu/ZHU_Training_Page/convective_parameters/skewt/skewtinfo.html).
Pressure is plotted on the y axis of a Skew-T diagram, and temperature is plotted on the x axis. Pressure decreases as you go up the y axis, just like it does in the atmosphere. Pressure is plotted on a logarithmic scale to approximate the way it decreases with height. The following chart uses data from [NOAA](http://noaa.gov); data includes pressure , height, temperature, dew point, wind direction, and wind speed. The green line is the dew point profile; the red line is the temperature profile. Just to the right of the diagram are wind barbs plotted with increasing height.
