 To find the mixed layer LCL, we use the method of equal areas to first determine the layer mean mixing ratio and potential temperature in the lowest 100 millibars. And doing that requires some visual estimations to select the correct mixing ratio and potential temperature lines. I want to show you an example of how this process works and some of the challenges that can occur in estimating equal areas. So let's start with the sounding from Midland, Texas at 12Z on May 14th, 2011. Since we have to focus on the lowest 100 millibars, which in this case is from just below the 900 millibar level to just shy of the 800 millibar level, we're going to zoom in on the bottom part of the sounding. The first thing we have to do is mark the top and bottom boundaries for our layer, and I've done that here in black. So this is the layer here that we're interested in finding the mean potential temperature and mixing ratio for. So the first thing you have to do to find the layer mean potential temperature is that we have to draw a line that's parallel to the local dry adiabats to create two equal areas that are labeled one and two here. Now this process requires some trial and error. Note that the environmental lapse rate in this layer changes from nearly isothermal to there's an actual temperature inversion toward the top of the layer. So you have to do your best to make the equal areas out of these odd shapes that result from the dry adiabat that we chose. Now just by visual estimation here we can see that the size of area two is pretty similar to the size of area one. So they're approximately similar. So that's looks like a decent choice. Again by trial and error to do the layer mean mixing ratio we have to create two equal areas and here I've marked them three and four. And you have to draw a mixing ratio line that's parallel to the local mixing ratio lines to create your two areas. Now this is a little more of a challenge. It requires eyeballing and the shapes are very different here largely because of this large leftward spike in the dew point profile that creates this very thin leftward pointing triangle. But you can see that if we moved our mixing ratio line to the left this triangle would start getting pretty small and area four here would get pretty wide. It would be clearly larger than area three. So this looks like a decent estimate for our layer mean mixing ratio but again it's the process of eyeballing and estimation. So finally if we connect the dry adiabat we chose and the mixing ratio line that we chose we have our mixed layer LCL. When we zoomed in on the lower part of the sounding we cut off the labels for the pressure levels but this is roughly 680 millibars. Because this sounding comes from NCAR we can actually check our work. The LCL that's labeled on these soundings is actually a mixed layer LCL and we can see here that we got pretty good results. We had about 680 millibars from the method that we used and the LCL that's marked on the sounding is pretty close to 680 millibars. Now you might get lucky sometimes if you have a sounding that already has a well mixed boundary layer in the lowest 100 millibars. And here's an example of that. If that's the case the environmental temperature profile is already dry adiabatic and that'll save you some work because the layer is already well mixed. So we don't need to find a special dry adiabat to create equal areas in the lowest 100 millibars. You can just use the dry adiabat to underlies the dry adiabat matching the environmental temperature profile to find the mixed layer LCL. And you only have to worry about finding the mean layer mixing ratio in cases like this.