Strong Storm; Where Will The Rain/Snow Line Set Up?

There is little doubt a strong nor’easter will track near or over Cape Cod Wednesday evening/Thursday morning.  There will be cold air in place so that most places in interior Southern New England (north and west of 1-95) will begin as snow.  The close track will allow for warm air to infiltrate Coastal New England, perhaps all the way to 495.  There will be a tight gradient of winners and losers with this storm.  In a matter of miles, snowfall accumulations will vary from 0 to 12″.   And wouldn’t you know, that line is going to be right near the Blackstone Valley.  Let’s discuss.


NWS PM Headlines

The Winter Storm Warning has been trimmed back a bit from this morning.  AHigh Wind Warning and a Wind Advisory are posted in Eastern MA.  There is also a Flood Watch in SE MA.


Light snow breaks out overnight.  Roads may be slick in spots tomorrow AM if left untreated.  That’s just a preview.  The main snow arrives just after lunchtime.

18z NAM hires simulated radar Wednesday 1 PM (image

By 5 PM, there will be heavy rain in Eastern MA and heavy snow in Central MA.  The rain/snow line really does want to mirror 495.  It could be raining in Mendon and Upton and snowing in Northbridge and Uxbridge.   Worcester looks to be safe for all snow.  The tricky part continues around Lowell, Lawrence, Meuthen, and Haverhill.  Wobbles of 5-10 miles will be the difference between a pasting wet snow or just heavy rain.

18z NAM hires Simulated Radar Wednesday 5 PM (image

As the low approaches the Cape tomorrow evening, the rain/snow line will fluctuate in the Blackstone Valley.  At times there will be heavy snow, at times heavy rain, at times sleet, sometimes all 3.  That means a back-breaking mix of heavy wet slop will fall.  It doesn’t really look like the snow will be able to get into the Boston metro area.  The track of the storm will allow for precipitation to shut off around or shortly after midnight in Central MA.   Temperatures will be marginal overnight so there are no worries for a flash freeze.   However, temperatures will dip below freezing Thursday evening so you’ll want to clear it up by then.

Now, there is a scenario painted by the EURO model of a track just offshore.  That keeps the warm air out of even Boston metro.  In that scenario, the Blackstone Valley stays all snow and gets a foot of snow.  In my scenario, its more like 3-6″.   The NWS compromises between both solutions and goes with 6-10″ for the BV.   I can’t wait for this winter to end.  Never have I ever seen so many snowstorms so difficult to forecast.

NWS Expected Snowfall Wednesday AM-Thursday AM

The highest uncertainty lies in the 4-10″ range just NW of the Boston to Providence corridor.


  1. Heavy wet snow to start tomorrow afternoon.  With winds gusts of 30-40 MPH inland, power outages possible.
  2. Rain/snow line will be right near 495.  It is possible the Mendon/Upton side of the river is rain while the Whitinsville/Uxbridge side is snow.
  3. Where it stays all snow, the evening commute will be nearly impossible with snowfall rates of 2-3″/hr.

High-resolution models tomorrow AM will help track the rain/snow line, as well as real-time satellite and radar analysis.  We have to go old school with this one.

-Zack Green


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