Saturation Mixing Ratio Lines -Lines of equal mixing ratio (mass of water vapor divided by mass of dry air -grams per kilogram) These lines also run diagonally but they are DASHED.

The above elements represent the lines you’ll use in order to measure the state of the atmosphere.  Here is the completed diagram:

This specific diagram is a recreation of a diagram used by The National Center of Atmospheric Research (http://www.rap.ucar.edu/weather/upper/).  The bullseye in the upper-left is unique to NCAR’s sounding diagram and will normally contain a blue dot within it.  The idea is to attempt and forecast the motion and type of supercell thunderstorms based on a climatology study of supercells.  You can find more information about this on NCAR’s help page for their upper-air information.

Now that we understand the basics of the diagram, let’s examine a basic plot that illustrates the environmental parcel and the dewpoint temperature.

The above diagram adds a few more elements of a completed Skew-T/Log-P Diagram.  Including the most important elements – The Date, Time and Location, which is illustrated underneath the diagram.  This plot for example states that it was a 12Z plot from Dodge City, KS on May 05, 2008.

Skew-T/Log-P Diagrams can be used to illustrate a sounding, which is created from rawinsonde data (weather balloon) or the diagram can be used to illustrate a forecast sounding which is created from numerical data imported from forecasting models such as the NAM, GFS or ETA.  In this example, we’re using actual data that was sampled.

The thick black line on the right represents the environmental sounding, or air temperature at each level throughout the atmosphere. The black line on the left represents the dewpoint temperature at each level throughout the atmosphere.  It should be noticed that these lines may vary in color depending on which system (or website) you’re using, but we’re using sold black lines here for illustrative purposes.

You may notice that the environmental sounding and dewpoint plot do not start at the bottom of the chart, but instead just slightly below the 900mb line.  This is simply because at the station where this was launched from (Dodge City, KS) the elevation is about 2,550 feet above sea-level.  So, the lines start at the level of pressure 2,550 feet above sea-level.

In the next installment of this primer to the Skew-T/Log-P Diagram we’ll examine this sounding and l determine some very important thermodynamic information such as CIN (cap strength), CAPE and LI, as well as a few other parameters that can greatly help you improve your convective forecasting abilities.