Here is a Skew-T that has had some environmental data pasted into it. Everyday balloons are sent up that take various measurements at specific levels of the atmosphere, two of them being temperature and dewpoint. What you are looking at here is essentially the result of a balloon with a thermometer and a hygrometer being sent into the air and taking measurements at 1000mb, then 950mb, then 900mb and so on. The red line is the temperature and the green is the dew point. So at 1000mb, the temperature is 28C and the dewpoint is 20C, up at 850mb the temperature has dropped to 24C and the dewpoint has held steady at around 20C. With our environmental soundings in hand, we can now take what we know about a Skew-T and turn it into something that chasers can use. The first thing I like to find is my LCL.
The LCL, or Lifted Condensation Level, is where the base of the clouds form and is simply the intersection of the dew points mixing ratio line and the temperature. The purple line follows the mixing ratio line near 20C until it runs into the red temperature plotting at about 28C. At this point our box of air has reached it’s saturation level and has to condense in the form of a cloud. When you hear chasers talk about high based or low based storms, the LCL is usually what they are talking about. When the cloud base is around 2000m or lower, that gets most chasers into the cars and on the road. Why? we’ll cover that in the final part of this Skew-T discussion.