'Bomb cyclone': 'Once-in-a-generation' winter storm upends US holiday travel

A dangerously frigid arctic air mass gripped a vast expanse of the United States on Thursday ahead of what could be one of the coldest Christmas Days on record, as a looming winter storm threatened to upend travel plans for millions of Americans. Leading into the holiday weekend, the impending storm was expected to bring blizzard conditions to several US states.