Powerful Storm Headed This Way

A major winter storm will impact all of New England by early tomorrow morning. This storm is already responsible for bringing historic icing to a large area of the southeast, extending from Texas to North Carolina. Before all is said and done, much of the large metro areas including Washington DC, Baltimore, Philadelphia and New York City will see 6-12 inches of snow. This storm may ultimately affect more than 1/3 of the US population.

Water vapor imagery showing massive size of this storm

The forecast for New England is not as clear cut. Once the system reaches the ocean, it will intensify rapidly, resulting in a sharp pressure level drop that we weather nerds call bombogenesis. Problem is, the track of this storm takes it over Cape Cod, which means a significant marine influence will cause precipitation type issues from the onset.

973 mb low is on par with a Cat 2 Hurricane!

This storm presents one of the most difficult situations that a forecaster can face. Small mesoscale factors, often missed by models, will have a tremendous impact on snowfall totals. Having said that, lets get to the details.

Precipitation Type

Massive shield of moisture will spread from south to north early tomorrow morning. Everyone will begin as snow starting between 6-8AM. This thing is juicy when it comes in so expect snow to start piling up quickly.

8AM heavy snow for most

After a few hours of heavy snow, we start to watch the wind direction and those surface temps. With an east-northeast wind, warm marine air will intrude at the surface along the immediate coast by late morning. How far that warmer air moves inland is questionable. Several factors at play. Marginal ocean temp (37 degrees), cold air just above the surface, precipitation intensity, all of these things will play a role in just how warm eastern Mass gets and how quickly.

I feel the changeover along the coast, including downtown Boston, will happen rather quickly, limiting snowfall totals. I believe that cold air will hang on for several more hours right around RT128 before a warm up later on in the afternoon. Areas along I495 and westward will remain all snow for much of this storm.

It is very plausible that metro Boston changes to a period of sleet and ice pellets in the early afternoon. One thing to consider is something we call dynamic cooling. Essentially, if the precipitation is falling hard enough, cold air from above can be dragged downwards into the shallow layer of warm air near the surface. Should this happen, surface temps may be just cold enough in some areas around Boston to avoid a quick changeover.

Finally I should mention the potential for flooding exists over southeastern MA. Upwards of 1.5 inches of moisture could fall on top of a decent sized snowpack. Huge puddles of standing water can create some localized flooding issues.
 

Winds

Winds will become quite strong once this storm bombs out. Sustained winds of 30-40 mph with gusts over 50 mph will develop along the coast. Wind direction will be crucial as well. Even a slight change in orientation to a more northerly direction will affect just where the coastal warm front sets up.


Wild Card!

As if this storm wasn't complicated enough, there remains a wild card towards the end of the storm. By early Friday morning, the center of the storm will be sitting off the Massachusetts coast, moving north east and intensifying. Several models are keying in on an impressive swath of heavy snow redeveloping over the area. Winds will sharply shift to the north, flooding the cold air back in. With wind gusts exceeding 35 mph and very heavy snow, we could see blizzard conditions to end the storm! Yes, we would get a mini blizzard as a finale. Its really something I have not seen before. Usually these back lash precipitation shields dry out but this one needs to be watched as it has the chance to really impact final snowfall numbers, especially along the coast.

Above you'll see the NWS Boston's official snowfall forecast. I think it looks good.  Big questions still remain along the coastal plane and about 10-15 miles inland. Again, some of this could fall on the back end of the storm.

This forecast is extremely volatile and things can change quickly. Hi-resolution models should start giving more answers tonight.