PHILADELPHIA (CBS) — With Arctic air in place and a favorable jet stream pattern for a coastal storm, a rare late season heavy snow fall is very possible for the Delaware Valley.

A winter storm watch will go into effect Monday Night through Tuesday Evening for most of the region.  This means there is the potential for 6″ of more of snow.

There still exists a lot of uncertainty regarding the storm track, precipitation types and snow amounts.  As expected this far out, model guidance continues to change with every new run.  The main energy for the storm will move onshore from the Pacific Ocean Sunday morning.  After that happens, the forecast should start to become more clear.

At this point, expect snow to begin late Monday night and continue through Tuesday, with the heaviest snowfall occurring overnight Monday & Tuesday morning.