My weather almanac noted a 31 degree overnight low of November 18, 2005. At that time it was earliest November freeze since 2000. Barbara Tufty's book, 1001 Questions About Hurricanes, Tornadoes and Other Natural Air Disasters mentions that frost usually occurs on clear, calm nights during the autumn when the air up top is moist. In South Louisiana frost occurs closer to the beginning of winter. When tender plants aren't affected, it's an example of light frost. Heavy frost contains crystallized water and doesn't kill sturdy vegetation. The most destructive frost to vegetation is killing frost while black frost or hard frost hits northern areas in late autumn when temperatures are consistently below freezing. A hard or black frost will cause leaf edges and plant tips to turn black as if they were burnt. Meteorologically, a freeze is defined as a period of time when the surface temperature of a whole air mass remains below freezing. That could occur for us in mid-January. Finally, Elmo is derived from Erasmus and St. Elmo was a fourth-century martyr, the patron saint of sailors. St. Elmo’s fire is a harmless glow appearing on high objects such as the topmast of a ship or the wing tips of a plane. It forms when misty air ionizes around an object. Electrons in the surrounding air are attracted toward these objects such as lightning rods or chimneys and a positive charge creates a green glow. Ferdinand Magellan’s crew, weary of stormy weather, was on the verge of a mutiny during their voyage around the world. Once they experienced St. Elmo’s fire on masts and spars they believed it was a sign that they were entering calm seas.