Strong Nor'easter To Bring Heavy Precipitation to New England

 An intensifying Nor'easter will bring heavy wet snow to parts of New England starting tomorrow morning. The National Weather Service has issued a *Winter Storm Warning* for Worcester County and Northwest Middlesex County. A *Winter Storm Watch* remains in effect for the rest of Middlesex County, Essex County, Hampden, Hampshire, and Franklin counties, Coastal New Hampshire, and Northeast Connecticut. 

NWS Boston Headlines Friday 12/4/2020 6 PM

6-12"+ are possible from Worcester County into Southern New Hampshire. This will not be a dry, fluffy snow. It will be a heavy wet, cement like snow. Winds will gust 30-45 MPH tomorrow afternoon into evening. This combination will result in widespread tree and powerline damage.  

General Overview

Despite marginal temperatures for snow, a major Nor'easter will manufacture enough of its own cold air to deliver a moderate to major snowstorm starting tomorrow morning. A rapidly deepening area of low pressure will will pass near or over the Cape and Islands. The storm already has the classic baroclinic leaf structure as it organizes along the Eastern Seaboard.

College of Dupage LWIR Satellite 

WPC Surface Fronts and MSLP Forecast Saturday 1 AM

Precipitation arrives in the form of rain between 4-7 AM from South to North. As rain rates increases, rain will begin to change to snow. This starts first in the higher elevations; Worcester Hills, Berkshires, and Litchfield Hills. The rain snow line will start around the Pike and 495 before collapsing south and east to around I-95 as the storm intensifies. The snow rates will approach, and in some cases exceed, 1-2" per hour. Some thundersnow is possible. The intense precipitation is key to creating temperatures cold enough to support snow. Eventually, temperatures will drop below freezing Saturday night as the low races into the Gulf of Maine. 

18z NAM Hires Simulated Radar Sat 3 PM (image Weather Models.com)

Where it doesn't snow, it will pour. Street flooding is possible anywhere south and east of a Providence -Boston axis. River flooding is not currently expected as Southern New England still has drought conditions. 

Strong winds from the deepening low will cause some tree and power line damage all over Southern New England. The strongest gusts will be in Southeast MA and Southern RI. The combination of 30-45 MPH winds and heavy wet snow will lead to numerous tree and power line damage in Central and Northeast MA. 

Snow Forecast

Let's be honest this is all you really care about! It is a tricky forecast. Since I am not a forecaster, let me present the National Weather Service forecast and add a few details. 

NWS Boston Snowfall Forecast

6-12" of heavy, wet, snow in Central and northeast Massachusetts will lead to damage. There is computer guidance that suggests 12-15" of snow is possible. I would bet on this coming true, in some places, likely in Northern Worcester County.  On the other hand, a weaker storm or a storm further west would support more rain than snow, even in Southern Worcester County. This is where the forecast is tricky. If the snow starts at 10 AM, up to 10" would be possible in the Blackstone Valley. If snow begins at 3 PM, it will be closer to 4 or 5 inches. Therefore, 4-10" is a reasonable forecast for Southern Worcester County. The amount of tree and powerline damage in a 4" storm would be considerably less than a 10" snowstorm. 

Thanks for reading the blog. I don't forecast daily anymore but I appreciate you taking the time to read my thoughts on the storm. All that is missing from making this a classic blockbuster is cold Canadian High Pressure. 

-Zach Green