Models are still too progressive with the arctic shortwave moving through Canada and Great Lakes region it is digging southward, not southeastward.  This will bode well for potential snowfall for Cape Cod on Wednesday.  If this shortwave can produce its own surface low, it will enhance the low-level flow over Gulf of Maine and Cape Cod, producing an inverted trough that can produce rapidly deteriorating conditions in a matter of minutes.  This inverted trough could produce up to 3-6" or more depending if it has time to mature and develop.  Models might be on target, but I am looking at the nowcast situation, we have a developing surface low east of NC coast, this is in a more northerly position than the models had 18 hours ago, also the precip shield is developing SW to NE and pivoting northward on the front end with a large push of heavy rainfall off the NC coast and into Hatteras, NC.  We have an additional energy behind the main arctic shortwave, that is diving through western Ontario, Canada and is pushing the overall momentum of the trough southward not eastward.  If this trough energy can dig south of Long Island, NY we can see up to 6"+ from the inverted trough.  Again the pivotal point will be tomorrow afternoon 18z observations.  Stay tuned!  I will issue a snowfall map tomorrow morning.