The National Weather Service uses two lightning detection methodologies, NLDN (National Lightning Detection Network) and LDAR (Lightning Detection and Ranging). The better method is LDAR, an accurate 3D mapping of electrical discharges which was developed by NASA. However, it currently only services central Florida and the Kennedy Space Center (Florida is one of the more lightning prone areas of the world, and lightning is not friendly to NASA’s spacecraft.) NLDN (see http://www.vaisala.com/weather/products/lightning/knowledgecenter/aboutnldn ) is the most reliable method covering the entire U.S. You can view U.S. lightning activity based on NLDN over the past 30 minutes here: http://thunderstorm.vaisala.com/explorer.html .