CHICAGO (Reuters) -A third of the United States faced the threat of severe weather on Wednesday as strong winds, snow and tornadoes threatened the Southeast, Ohio Valley and East Coast, while a fierce winter storm bore down on the Northwest. A day after many Americans basked in a spell of summertime warmth in what is normally the coldest time of year, some 127 million people living in the eastern half of the nation were under wind advisories as colder weather returned. Gusts could reach 45 miles (72 km) per hour, the National Weather Service said.