WASHINGTON, Dec 22 (Reuters) - The United States faces "dangerous and threatening" storms in the days before Christmas, President Joe Biden warned Thursday from the White House, and Americans who plan to travel to visit family or friends should leave right away. “It’s dangerous and threatening, it’s really very serious weather and it goes from Oklahoma all the way to Wyoming and Maine. ... So I encourage everyone to please heed local warnings," Biden said in the Oval Office.