In the United States, a historic winter storm whipped across the central Plains and Midwest early Tuesday. The National Weather Service forecast blizzard conditions across portions of eight states, from Oklahoma to Michigan and winds gusting to 40 miles per hour are expected. Oklahoma was under a state of emergency and Missouri mobilized 600 National Guard troops to help cope with the onslaught. The leaders of several states, many of which have already had a difficult winter, also commandeered their forces even as they urged people to stay home. The expansive storm will ultimately affect about three-quarters of the United States, stretching more than 2,000 miles. The weather service has posted winter storm warnings, watches or advisories in some 30 states. Heavy snow is predicted along a sweeping 1,500-mile arch, starting in north-central Texas and ending in southern Maine. The winter weather is prompting airlines to cancel flights by the hundreds and numerous carriers are letting customers make changes to their itineraries.