Winter Storm Headlines Issued Ahead of Thursday-Friday Storm

The National Weather Service in Norton, MA has issued a *Winter Storm Watch* for interior Southern New England a *Winter Weather Advisory* for communities inside 495 and RI/S CT.

NWS Boston Headlines (CLICK TO ENLARGE)

The watch begins at 7 PM tomorrow evening and continues until 7 AM on Friday.  There is little doubt that precipitation begins as snow.  The snow will change to sleet and freezing rain and eventually plain rain.  The exact timing of this transition is still a bit of a wild card.  Many communities will also end as snow Friday morning/early Friday afternoon as the storm races into the Gulf of Maine.  The highest uncertainty is from Hartford to Worcester to Lowell where 6+" of snow is possible if it stays all snow.  Let's discuss.

General Overview

WPC Surface Fronts/Precipitation Thur 7 AM, 7 PM Fri 7 AM, 7 PM

The storm system will lift northeast tomorrow, spreading snow, sleet, freezing rain, and rain up the Eastern Seaboard.  Working in favor of snow is the cold air mass already in place across the Northeast.  Temperatures tomorrow will be in the upper 20's/low 30's.  By 7 PM temperatures will be back in the upper 20's.  That sets the stage for frozen precipitation to begin as the storm begins to reform near the Mid-Atlantic coast. 

18z NAM 3km Sim Radar/P-Type Thurs 7 PM (image Tropical Tidbits)

The majority of the snow falls during the 7 PM-midnight time frame.  Solutions diverge as the clock turns to Friday.  The EURO model makes this a Cinderella snow and keeps the fun going past midnight.  The American NAM turns it into Sleet-fest 2018.   The NAM has trended a bit colder in its latest run.  Working in the NAM's favor is the calendar.  The "warm" sea surface temperatures mean any wind from the east will end the snow and cause a change over to sleet and then plain rain.  A storm track along Long Island and over the Cape would also favor a change over to sleet and then rain or drizzle.

This is the EURO at 11 PM tomorrow night.

12z EURO P-Type/Mean Sea Level Pressure Thurs 11 PM (image WeatherModels.com)

The NAM at the same time.

 

18z NAM 3km P-Type (image WeatherModels.com)

What is causing these differences?  Subtle differences in the temperature profile, which is not uncommon at this time range.  The calendar and the track of the low certainly favors a change to sleet and rain.  Despite that, the temperature profile does support heavy snow especially with heavy precipitation.  So where does that leave us?

Impacts/Totals

If you are traveling home from Hartford or Providence, leave a bit early as the beginning of the snow will fall at the end of the evening rush.  The commute from Boston and Worcester should be fine.

The initial burst of snow will drop 2-4" of snow, with rates near 1"/hr between 9 PM-12 AM.  As the upper levels warm, snow changes to sleet and then freezing rain or drizzle.  It will be tough to dislodge the cold so this will likely continue until sunrise.  This happens first in RI and Eastern Massachusetts, especially inside 95/128.  Then it will work towards 495, the Pike, and Rt 2.  An extra hour or two of snow means an extra inch or two of snow.    As the precipitation intensity decreases, the snow/sleet will turn to drizzle or freezing drizzle.  This really is a mess!  

Allow of extra time Friday morning because the commute will be slow, especially those coming from Central and Northeast MA.    For school administrators and public works departments, my advice is to plan for 4-7" of snow as well as 2-3" of snow followed by sleet and freezing rain.  Here are the NWS totals for both snow and ice.

NWS Snow/Ice Forecast (CLICK TO ENLARGE)

As the storm departs late Friday morning/early Friday afternoon expect one final round of rain south of the Pike and snow north of it.  Winds increase behind the storm and cold air returns for the weekend.    I will be at a conference tomorrow but I will get an update on the blog one way or another.

-Zack Green