We are still under the influence of a maritime Pacific air mass and this once again creates marginal temps at the lowest 1000 feet of the atmosphere. Throw in no blocking from high pressure in Canada or New England and you get a storm wanna be.
MARITIME POLAR AIR MASS
The source region for mP air is over cold ocean currents or high latitude ocean waters. This air does not have as much moisture content as mT air. Since mP air is always near saturation, orographic lifting of the air mass can produce widespread rain or snow.
This air mass is notorious for producing fog, drizzle, cloudy weather and long lasting light to moderate rain. The temperature of mP air ranges from just above freezing to below 70 degrees F. mP air is modified as it moves over elevated terrain.
On the windward side of mountain ranges, mP air can produce an abundance of rain and snow. Once on the lee side of mountains, the mP airmass modifies into a continental airmass.
These air masses produce cold fronts but the air is not as cold as polar or arctic fronts. They are often termed "Pacific fronts" or "back-door cold fronts". Maritime Polar air occurs frequently in the Pacific Northwest and to a lesser degree in New England.
MARTIME NOW...ARCTIC LATER
MODELS MODELS MODELS
If this storm ends as nothing more than a light event offshore the GFS will win the mid and long range model war on this one. The Europoean model took the early lead this fall with the mid and long range game so this would make it 1 for the GFS and 2 for the Euro.
The Operational European model above shows just enough cold air to support some wet snow but this model may be 1-2 degrees too cold. Even if this is snow the this model only shows the following precip for the event.
Philadelphia .13" (Sat Night into Sunday AM)
Allentown .18" (Sat Night into Sunday AM)
Wilmington .14" (Sat night into Sunday AM)
Baltimore .15" (Sat. Evening into Sunday AM)
DC Metro .17" (Sat. late day into Early Sunday)
NYC Metro .20" (Sunday early AM to Sunday PM)
Temps are warmer at the surface at 34-37 at night and 42 during the day. This would mean the wet snow, if it's all wet snow, would be not sticking to the ground.
The Euro ensembles added the moisture but it still a marginal temp event. The coldest air is in the lightest moisture so this overall is still not a huge event. The map on the right is the temps at 5,500 feet and the rain snow line is the blue dotted line on the left map.