Heat waves and cold snaps are typically good news for Wyoming coal, which goes almost entirely to fueling U.S. power plants. Natural gas takeoverThe primary factor for coal’s declining share of energy production in Wyoming has been the conversion of several coal-fired power generation units to natural gas in recent years. A multiple-utility power outage last fall knocked out a coal-burning unit at Glenrock’s Dave Johnston Power Plant and it remains off line. The Naughton, Jim Bridger and Dave Johnston power plants are all beyond 50 years old, approaching the end of their functional life. A University of Wyoming analysis suggests the average age of power plants served by Wyoming coal is 41 years.