Here’s what we know about Saturday’s nor’easter

I wrote about the potential for a significant early December nor’easter Thursday, and that potential is going to be realized.

There’s more agreement that a major coastal storm is going to develop Saturday and head up into the Gulf of Maine on Sunday. This is a complicated system with a lot of energy. The southern and northern jet streams will merge their respective areas of energy and moisture and create the storm.

The northern and southern branches of the jet stream are getting ready to converge east of New England Saturday.COD WEATHER

Areas that see mostly snow from this could receive well over 6 inches of heavy, wet snow. The most likely spots for this are going to be Worcester County, Northern Middlesex County, and perhaps even parts of extreme Western Essex County.

Heavy snow is likely Saturday afternoon with a rate of over 1 to 2 inches per hour possible in some places.Dave Epstein

This storm is going to intensify rapidly during Saturday and although temperatures may be marginal at the surface, as the precipitation comes down very hard it will pull cold air from above and change the rain to snow. These types of storms are very challenging because a difference of just a few hours when that change occurs will make a huge difference in what you end up seeing in your front yard. Notice the tight gradient in snowfall totals around Boston. I will refine this later today, but amounts will vary rapidly from the coast to a few miles inland.

Saturday afternoon temperatures will be in the 30s.COD WEATHER

The rain will start Saturday morning and change to snow in the higher elevations first. The changeover line then pushes east, reaching Boston between 3 p.m. and 5 p.m.

Rain and snow will be falling Saturday afternoon across eastern Massachusetts.WeatherModels.com

The intensity of the precipitation is a concern. There will likely be a band of over 2 inches of snow per hour somewhere west of the coastline. This type of banding situation is very difficult to nail down, so that is the reason for a wide range in snowfall predictions.

The exact track of the storm will be critical to where that band ends up setting up. If the storm were to take a farther inland track, then the threat of heavy snow in Greater Boston would be lower because temperatures would probably stay a little too warm and we would just see some snow at the end.

A nor’easter moves along the coastline Saturday and into the Gulf of Maine Sunday.Tropical Tidbits

There will be wind with this particular storm, but the heaviest winds will be out over the Cape and the islands, especially right at the water where winds could gust over 50 miles an hour for a time. You can see on the loop below the strong winds move up across Cape Cod and then toward Maine.

A core of strong wind as the storm moves over Cape Cod and Cape Ann Saturday.COD WEATHER

I am concerned about power outages in the area that receives the heaviest snow. The good news is that the leaves are now off the trees, but 5 or more inches of heavy, wet snow can take down tree limbs and definitely cause outages.

The storm will wind down Saturday evening and by Sunday, it’ll mostly sunny with temperatures in the 30s. Unlike our pre-Halloween storm, you will need to shovel. This time of the year, with the low sun angle and temperatures only in the 30s, will not allow for much melting. It will be in the 20s Sunday night, so if you’ve left slush on the ground it’s going to freeze solid.

I don’t see any more storms in our future right now and temperatures will get back into the 40s next week.