Snow: Getting late

Five days before the equinox, it's beginning to feel a lot like five days before the winter solstice.

The air the last two days has had a wintry bite, and the National Weather Service forecast is calling for a chance of minor snow accumulations around Philly during the weekend.

While the region has weathered some cosmic late-season snowfalls -- including the 19.4 inches of April 3-4, 1915, and the great equinox storm of 1958 when 3 feet was measured in Chester County -- snow from March 15 on is the anomaly in Philadelphia.

Of the roughly 175 feet of snow that has descended upon Philadelphia in the period of record dating to the late 19th Century, only 10 percent of that has fallen from the Ides of March on.

Even when cold air is available, the mortal enemy of accumulating snow is the obvious: The sun.

The sun's wattage undergoes a tremendous growth spurt in February.

Drexel University's Fred House, an expert on the solar radiation budget, has estimated that on average, the sun aims 329 watts per square meter to the top of the Earth's atmosphere above Philadelphia.

That figure ranges from 156 watts at the winter solstice to 484 watts at the summer solstice, and February, the wattage increases from 208 watts on Feb. 1 to 280 at the end of the month. That's beats the average daily rate by about 60 percent.

For now, it may feel more like we're in the 156-watt mode, like it's time to change the lightbulb.

But despite the chill, any snow will have a hard time surviving the flight, let alone the landing.