The question is a December evergreen: Are we going to have a White Christmas?

The answer this year, is almost certainly no - the same answer as in most years. So why does the question keep popping up every Christmas season with the regularity of bad holiday music?

Around here and for an overwhelming majority of the nation's population - not to mention Bethlehem, in the Holy Land - snow at Christmas is decidedly the exception.

Only seven times in the last 56 years has an inch or more of snow been on the ground officially in Philly on Dec. 25, most emphatically in 1966, when a foot fell from a storm that continued into the early-morning hours.

So why the snow fixation? "I think it's a cultural thing," said Gary Szatkowski, meteorologist in charge of the National Weather Service, which sees rain for Wednesday, and a dry, cold Christmas.

The late Tristram Coffin, founder of the University of Pennsylvania folklore department, would agree. He attributed the snow connection to an extraordinary chain of developments that began in the fourth century, and snowballed, so to speak in the 19th and 20th.

The "Santa Claus" tradition is a mutation of the legacy of a bishop who died in 342, said Coffin. That would be St. Nicholas, of course. It is believed he wore red robes, although accounts of his life weren't written until 500 years after his death.

In the Dutch tradition, on the anniversary of his death, Dec. 6, St. Nicholas would appear in the sky on a white horse, and children would leave hay in their wooden shoes for the steed.

In the New World, the legend underwent an extreme makeover. Washington Irving, based up in New York Dutch country, is credited with popularizing the image of "Santa Claus," introducing an elfin "jolly St. Nicholas" character in his Knickerbocker History of New York in 1809, according to the St. Nicholas Society.

But a poem credited to a professor of Greek and Oriental literature named Clement Clarke Moore set off the avalanche that has forever buried Christmas in snow, according to Coffin, who died in 2012.

It was called "An Account of the Visit of St. Nicholas," and appeared in 1836 in the Troy (N.Y.) Sentinel. We know it more by the opening line " 'Twas the night before Christmas."

The poem added reindeer and sleigh as the gift-delivery vehicle, which naturally required snow, as surely as 18-wheelers require road surface.

Of note, the poem appeared near the end of the "Little Ice Age," an era dating to the Renaissance when at least parts of the planet were chillier than they are today, so snow likely was more common in December in the Mid-Atlantic and Northeast.

By the 1940s, Decembers may have tempered a bit, but reality could not stand up to the power of a Jewish songwriter. Irving Berlin's song "White Christmas" debuted in the 1942 movie, Holiday Inn, sung by Bing Crosby.

It was reprised in the schmaltzy, if not addicting, film White Christmas.

An Inquirer informal survey shows that just about 99 percent of all Christmas movies ever made have snow in them - most of it truly unnatural.

Ironically, one of the most realistic Christmastime weather scenes on film occurs in White Christmas.

When Bing Crosby and Danny Kaye first arrive in Vermont, they see nothing but snowless evergreens and ground - and this was years before global warming.

December warm spells are common, even in Vermont, and especially around here.

The upper air and oceans haven't quite cured into winter mode, even though the sun is approaching its weakest period in the Northern Hemisphere. But the lag between the weakest sun angles and the coldest weather usually is a few weeks.

Over 85 percent of all snow in Philadelphia has fallen after Jan. 1, and about 90 percent of all December precipitation has been rain.

Expect more of it Christmas Eve. As for snow, said Szatkowski: "There's always next year."