Supporters of German Chancellor Angela Merkel's Christian Democratic Union (CDU) party cheered and sang as the first exit polls put their share of the vote at 42 percent.
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Guillier conceded a "severe defeat" defeat to his supporters as the result came in.
The outage struck Hartfield-Jackson Atlanta International Airport at around 1pm local time, stopping all outgoing flights.
It will be a chilly day for many parts with the highest temperatures, about 10 Celsius (50F) in the far northwest.