In Boston and New York City, the cold may feel most harsh late tomorrow and tomorrow evening. The temperatures will not have hit bottom by then, but gusty winds will sharpen the chill.
One concern: the chance of cold frontal snow squalls that could move all the way to the East Coast tomorrow night. Sudden snow squalls have been implicated in chain reaction collisions that turn deadly and damaging.
These two maps show the change from the very, very cold flow likely this Saturday to the much milder Pacific-origin westerly flow later next week.
When we look more closely, we see a variety of disturbances embedded in the main current, each capable of temporarily increasing or cutting off the chance of snow. This map shows the setup:
This map shows the circulation around the offshore storm and a larger but less intense storm moving into the Great Lakes. With this sprawling storm likely to be in the region for several days, the weather can vary widely.
...speculation about a snowstorm Monday or Tuesday, and one is still possible. However, timing and placement remain elusive. This map shows the GFS ensemble mean "solution" for Tuesday morning showing snow just off the New England coast. Watch this story evolve on accuweather.com all weekend.
As we look father out this month, it looks cold for the Great Lakes and Northeast (as well as deep into the South) in the middle of next week but milder the following week. This map, for next Wednesday, shows a cold flow from way north in Canada.
A few tornadoes can also occur, especially from Mississippi and Alabama to Kentucky. This map shows the areas of potential severe weather through tonight as forecast by the NWS Storm Prediction Center.
A less prominent but strengthening band of snow showers was moving southeast across Wisconsin. That feature is the one that would cause snow showers tomorrow morning in the Northeast Corridor.