the pilot-in-command's improper decision to take off into deteriorating weather conditions (including turbulence, gusty winds, and an advancing thunderstorm and associated precipitation) when the airplane was overweight and when the density altitude was higher than he was accustomed to, resulting in a stall caused by failure to maintain airspeed. Contributing to the pilot-in-command's decision to take off was a desire to adhere to an overly ambitious itinerary, in part, because of media commitments.