What is a Skew-T sounding?
1000 mb ......300 ft
Before I get stated you will need to know a few basic things. Below are two images of blank Skew-T, with labels for what each line means.
That explains what all the lines are on a blank Skew-T. I hope it wasn't too bewildering. Because it is very Important that you understand what the lines mean as we move ahead. Now I will go into more detail about adiabatic processes. This part of the lesson will focus on the role these processes play in severe thunderstorm development. The next Skew-T will show the temperature and dewpoint temperature plotted on the chart. I will also go into a bit of detail how these two variables are used to make a forecast. Again, on severe thunderstorm development. However, an atmospheric sounding can be used to forecast all sorts of weather. Atmospheric analyses involves a good understanding of thermodynamics and higher math. However, I will try and keep the use of science and math at a minimum. After all, the purpose of this blog post isn't to make you a meteorologist; instead it's meant to give you a basic overview of what a Skew-T is used for.
The next two charts are based off of a parcel lifted from the surface. But speaking pragmatically, this wouldn't happen most of the time. normally lift will be “mixed” through the lowest 100 millibars. but doing it this way will make things easier to understand.
When an unsaturated parcel is lifted from the surface, it will cool at the dry adiabatic lapse rate until it reaches saturation. This elevation is called the lifted condensation level, or LCL, and represents the level in the sky where you see the cloud base. To find the LCL on a Skew-T, you follow the dry adiabat from the temperature at the surface, and follow the mixing ratio line up from the dewpoint at the surface level, until the two intersect. This level is where the LCL is located. Once a parcel reaches its LCL, it is said to be saturated, then it will start to cool at the moist adiabatic lapse rate.
These parcels of air are usually cooler than the air around them; when they reach the LCL something else needed to keep lifting. Once they are lifted to the point where the parcel temperature is greater than the environmental temperature, the air is unstable and will continue to rise on its own. This is called the Level of Free Convection, or LFC. It then rises freely, without needing a source of lift, cooling adiabatically until it cools below the environmental temperature and stops rising. The level at which it reaches the environmental temperature and becomes stable again is called the Equilibrium Level or EL. This line is often called Parcel lapse rate. This line shows the temperature path a parcel would take if raised from the Planetary Boundary Layer. This line is used to calculate the LI, CAPE, and CINH (which I will get into in the next section), and several other thermodynamic indices that are beyond the scope of what I want to cover in this post. The Skew-t below shows this.
I tried to keep things easy to understand but at the same time be thorough..I hope you enjoyed reading and learning about Skew-T diagrams...If you have any additional questions that aren’t answered here, Let Andy or I know, we would be happy to answer them.