Weather forecasters are predicting wild temperature swings across the eastern U.S. Wednesday was expected to be another scorcher before temperatures plunge as much as 30 degrees. On Tuesday, at least 50 heat records were broken and 21 places hit triple-digit temperatures. About 127 million Americans are under some kind of National Weather Service heat advisory, down from more than 150 million Tuesday. The sizzling temperatures sent utilities scrambling to keep the air conditioning and lights on because of the massive power demand.