Are we going to have a White Christmas? – (the short answer this year evidently  is no) – is a question that keeps popping up every year by mid-December, if not sooner.

But the better question might be: How did Christmas snow become so embedded in the popular consciousness?

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.

The best explanation we've come across for this seasonal snow fixation was offered Penn folklorist Tristram Coffin, who died in 2012. We know of no one else who devoted so much time and energy to the question.

According to Tristram, the answer rests in an extraordinary chain of events that begins in the fourth century during the reign of the emperor Diocletian, 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. That would be St. Nicholas, of course. It is believed he wore red robes, but keep in mind that accounts of his life weren't written until 500 years after his death.

On the anniversary of his death, Dec. 6, Dutch legend had it that he 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."

But a poem accredited 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.

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 Midatlantic 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 yet somehow endearing, if not addicting film, White Christmas, which, by the way, has some better Berlin songs, in our estimate.

Our own informal survey shows that just about 99 percent of all Christmas movies ever made have snow in them – most of it truly unnatural.

Movies, we found, often have a hard time with weather, particularly snow.

Ironically, one of the most realistic Christmastime weather scenes we've ever witnessed in a movie occurs in White Christmas.

When Bing 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 is 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 the Philadelphia has fallen after Jan. 1, and about 90 percent of all December precipitation has been rain.

Personally, as much as we would love snow for Christmas, in temperate climate's bare trees constitute one of our most underrated aesthetic pleasures, and that's something we can count on almost every Christmas.