Higher humidity and temperatures heading to the upper 80s occasionally activate afternoon thundershowers. We may experience some "convective showers" Saturday. We're not expecting any "heat bursts" this month however when they occur, 100 m.p.h. hot air blasts are possible. In Portugal on July 6, 1949 meteorological observers reported a temperature increase from 100 to 158 degrees F in two minutes.  In the early evening of June 15, 1960 at Lake Whitney, Texas, the temperature rose to 140 degrees F in a few minutes with winds of 80 to 100 miles per hour. A nearby cotton field was completely scorched and car radiators boiled over.  A heat burst traditionally forms after sunset as warm, moist air that feeds a thunderstorm cuts off and the storm collapses.  The rain in the top of the thunderhead drops into cool, dry air, becomes compressed and hits the ground as a hot dry wind. What makes the heat burst so unusual is the high rate of speed at which the down draft travels.