Snow: Forecasts inch up

Scattered snow placed a powdered-sugar coating on parts of the region this morning, and a period of heavier snow scooted to the northeast of the region.

It wasn't much, but it could be a big player tomorrow night, according to Louis J. Uccellini. He runs the National Centers for Environmental Protection and one of the nation's foremost winter-storm experts.

It already has had an impact on the forecasts.

At daybreak today, the official National Weather Service forecast called for paltry snow amounts in the immediate Philadelphia area.

A winter-storm watch was posted for Bucks and Montgomery Counties, but that could be viewed as precautionary.

At midmorning, everything changed. The U.S. North American Model was showing a signficant snowstorm. The watch was expanded, and the totals ramped up.

Uccellini said that the basic outlines of the storm hadn't changed much in the last several days. Government reconnaissance planes over the North Pacific and, more recently, the Gulf of Mexico, have been monitoring the storm's progress.

The forecast had called for a storm to migrate from the Gulf of Mexico and push enough warm air across the region to limit the storm's snow content.

As it gave way to a storm off the Mid-Atlantic coast, the precipitation was to turn to all snow sometime before it ended.

However, that small system this morning evidently perturbed the atmosphere enough to keep colder air in place all the way to northern Virginia.

The forecasts consistently have seen substantial liquid. This morning, they turned substantially whiter, thanks to the prospects of colder air.

By day's end, the National Weather Service snow map was showing 6 to 8 inches in the immediate Philadelphia area.

But don't be surprised if that changes tonight and even tomorrow. Said Gary Szatkowski, who runs the weather service's Mount Holly office, "be prepared for some more iterations of the snow map."