Snow: 6 p.m. update

It was supposed to be a "nuisance" snow, but now it is taking on a disruptive look for folks with travel, shopping or other plans tomorrow.

The National Weather Service's forecast accumulation map now shows close to 4 inches in Philadelphia, with more in South Jersey. It looks to start around 9 a.m., and continue into the evening, and it will be cold enough to stick.

That is quite an upgrade from the morning forecast, but it's by no means a done deal. "It's a tricky system," says Corey Mottice at Accu-Weather Inc.

An area of low pressure in the upper atmosphere will have pieces of energy rotating around it, he said. The weather service also is looking for a coastal low to form, and today's later model runs all show more moisture streaming into the region.

As for Tuesday's snow, the computer models predictably are disagreeing, and you can expect big changes in the forecast between now and Monday. 

The potential exists for a major snow, and the official weather service forecast lists a 60 percent chance of snow Tuesday.

You might want to follow the discussions of the experts and enthusasts posting on the American Weather Forums.