White Christmas (weather) by Bing Crosby from the film "Holiday Inn", is the best-selling single of all time and speaks nostalgically of a traditional white Christmas. The definition of "white Christmas" varies. In most countries, it simply means that the ground is covered by snow at Christmas, but some countries have more strict definitions. In the United States, the official definition of a white Christmas is that there has to be a snow depth of at least at 7:00 a.m. local time on Christmas morning, and in Canada the official definition is that there has to be more than on the ground on
White Christmas (weather) snow. In the United States the notion of a white Christmas is often associated in the American popular consciousness with a Christmas celebration that includes traditional observances in the company of friends and family. "White Christmas" is an Irving Berlin song reminiscing about an old-fashioned Christmas setting. According to research by CDIAC meteorologist Dale Kaiser, the United States during the second half of the 20th century experienced declining frequencies of white Christmases, especially in the northeastern region. The National Climatic Data Center based the probability of a white Christmas ( of snow on the ground) at selected cities upon the