About that ‘White Christmas’ dream, and other snowy thoughts at the solstice

With a predictable precision that may forever elude meteorology, at 10:03 a.m. Philadelphia time Sunday, the sun will beam its most direct light of the year on the Tropic of Capricorn and the astronomical winter will begin in the Northern Hemisphere.

Sunday indeed is going to be the shortest day of 2025, with just over nine hours and 23 minutes between sunrise and sunset.

On the bright side for those who have about had their quotas of premature darkness, the day length would be a mere one second shorter than Saturday’s, and on Monday, we gain two more seconds. On the dark side, Sunday’s sunset is a full three minutes earlier than that of Dec. 12. (And don’t ask about sunrise.)

Plus, in two weeks the night skies will become considerably brighter with the rising of the last of four consecutive “super moons,” which will peak on Jan. 3.

Whether the brightness would be enhanced by snow cover is another matter: Meteorology has a long way to go to catch up to astronomy in terms of predictability.

In the early going, Philly is more than halfway to last winter — with 4.2 inches of snow, vs. 8.1 for the entire winter of 2024-25.

In the short term, this is a peak time for a perennial question.

“No” almost always is a safe answer in Philly, and all along the Northeast Corridor from Washington to Boston. And “no” it is this year, says Bob Larsen, senior meteorologist at AccuWeather Inc.

With a white Christmas defined as an inch of snow on the ground at Philadelphia International Airport on Dec. 25, the National Oceanic and Atmospheric Administration officially posts about a 1-in-10 chance that it will happen in any given year in Philly.

So why the fascination? Blame Irving Berlin, composer of “White Christmas,” and Bing Crosby, who crooned the most famous version, but probably a bigger impetus was the poem “A Visit from St. Nicholas,” published in 1823 and credited to Clement Moore.

The poem cast Santa Claus as personally delivering gifts via his sleigh. This predated Amazon Prime. That pretty well cemented the Christmas/snow relationship.

Philly gets most of its major bigger snowstorms from nor’easters, which tap the moisture of the Atlantic Ocean. The onshore winds can also import warm air from the ocean, and this time of year ocean temperatures still are well into the 40s. That’s why snow changes to rain so often around here early in the winter. It takes time for the ocean and the snow-making upper atmosphere to cool, and the snow season peaks in late January into February.

That doesn’t mean a storm can’t pop before then.

It so happens that next month is the 30th anniversary of Philly’s record 30.7-inch snowfall of Jan. 7-8.

It was so unbelievable that the record wasn’t verified officially until four years later, after NOAA commissioned a federal investigation. It turned out that the snow was not actually measured, but inferred from the liquid content of the melted snow and the air temperatures.

The investigators — David Robinson, the Rutgers University professor who is the longtime New Jersey state climatologist and an international snow authority, and Jon Nese, who then was the Franklin Institute meteorologist — affirmed the total.

They concluded that the snow reports in neighboring towns were close enough to support PHL’s.

In the standard language used by the National Weather Service and commercial outfits, that certainly qualified as a “heavy” snowfall.

But it was the antithesis of “heavy,” at least in terms of relative weight. Snow comes not only in different shapes, but also in very different weights, depending on the snow-to-liquid ratios. On average around here, an inch of liquid yields about a foot of snow, a 12-1 ratio.

However, when temperatures are close to freezing as they were last Sunday, the snow has a higher liquid content and is thus heavier. On Sunday, 5 inches may have felt more like 8 to the average shovel. That’s heavy snow.

When it’s cold, as it was on Jan. 7, 1996 — temperatures were in the teens during the day — the flakes are way drier. The ratio for the storm was closer to 20-1, and overall the flakes were a whole lot lighter.

“Heavy” snow “applies to visibility ratios,” said Jim Eberwine, longtime meteorologist with the National Weather Service local offices, adding it might be time to reconsider the use of that adjective.

“Some things should be updated,” he said.

How about: Snowfall rates can be intense at times?

The solstice also marks the beginning of the astronomical summer in the Southern Hemisphere, so residents south of the equator probably won’t be using snowblowers for the next several months.

In fact, they won’t be seeing a whole lot of snow there during the winter. It snows robustly in the Andes and other mountain regions, but not in major population centers, the AccuWeather people note.

NOAA’s National Center for Environmental Information doesn’t bother to track snow cover in the Southern Hemisphere, for a couple of reasons, including that it’s 80% covered by climate-moderating water.

Plus its major cities are located at latitudes where snow is scarce.

By contrast, the Northern Hemisphere has a plentiful supply of metropolitan areas that experience ruler-worthy snowfalls, including Philadelphia.

Making seasonal snow forecasts in this region isn’t quite like picking lottery numbers, but reasonably close. Seasonal totals have varied from 78.7 inches in 2009-10 to nothing in 1972-73. NOAA’s Climate Prediction Center doesn’t touch the stuff.

The guesses for this year are in, and here is a partial list with what’s out there: The “normal” season total is 23.1 inches.

Fox29 — 16 inches

AccuWeather/6abc — 14 to 18 inches

CBS3 — 18 to 24 inches

Arcfield Weather — 22 to 26 inches

WeatherBell Analytics — 22 inches

One prediction they all have in common: The winter of 2025-26 will out-snow that of 2024-25.

That won’t be hard.