SkewT or Tephigrams are graphical representations of the airmass that indicate the temperature, humidity, dew point, wind speed, direction, thermal strength and lapse rate through the atmosphere in one go! Once you understand them, they are a very useful extra aid when trying to work out what is going to happen with the weather on a particular day. This is a great lecture that gives enough to make sense of them quickly, so you can make more informed decisions about where and when to fly. Windy.com has a simplified version that is very handy when looking at the forecasts further out than RASP goes when you want to understand roughly what is going on with the airmass. This lecture was given by Sean Staines, chairman of the Wessex club who's been flying for 25 years and to whom I am forever grateful as he sent me on my first XC back in 2004!