National Weather Service Issues Winter Storm Warning

The National Weather Service Boston office has issued a *Winter Storm Warning* for most of Southern New England, except for the South Souths of CT, RI, MA and the Cape and Islands.

NWS Boston Winter Weather Headlines

 From the NWS

"Snow will overspread the region between 1 and 4 am Friday morning. The snow will quickly become heavy falling at the rate of 1 to 2 inches per hour at times Friday morning. This will have a significant impact the Friday morning commute. The snow may change to a period of sleet near and especially south of the Massachusetts Turnpike by late Friday morning. Any mixed precipitation should change back to snow later Friday afternoon and early evening before ending."

NWS Precip End Time

The heaviest snow will fall Friday morning. Consider delaying any travel until the afternoon, if possible. If you have to be on the roads, allow yourself some extra travel time. How far north will the rain snow line venture? I still think sleet could mix in all the way to the MA/NH border. 

18z HRRR Simulated Radar 3a-12a (Image Weathermodels.com )

However, anyone in the winter storm warning can expect 6-10" and 1-1.5" of sleet. The sleet will compact the snow even further, so the actual snowfall depth will be 3-6" in these places.

NWS Boston Snow Forecast 

Is this the last of the snow for the winter? I doubt it and it wouldn't be fair to anyone if I were to jinx it. 

Blizzard, Winter Storm Warning's Posted For Southern New England

 

The National Weather Service Boston office has issued a Blizzard Warning for parts of Southeast Connecticut, all of Rhode Island, and all of Eastern Massachusetts. A Winter Storm Warning is in effect for the rest of Worcester County, Eastern Hamden, Hampshire, and Franklin Counties, and most of Connecticut. 

• A blizzard warning is issued when visibility is less than ¼ of a mile due to falling or blowing snow, with sustained winds or frequent gusts over 35 MPH for 3 consecutive hours. 
• A winter storm warning is issued when 6” of snow is expected in less than 12 hours OR 8” of snow in 24 hours. 

For a refresher on how the storm will form, please see last night's blog.

Big Picture

Here are the latest headlines from the National Weather Service.

NWS Boston Headlines

The headlines are in effect from Midnight tonight until 5 am Sunday. The main reason Worcester County is not under a blizzard warning is due to uncertainty of the winds meeting the blizzard threshold. The current national radar does not look ominous at all.

College of Dupage Weather Center Simulated Radar

The surface map from 10 AM this morning is a bit more busy. You can see our 2 pieces of energy moving towards the Carolina coast. A new low is beginning to form off the Southeast coast.

WPC 15z Surface Analysis (10 AM) 

This will be our storm. You can almost see the baroclinic leaf beginning to take shape on the low level water vapor satellite loop. The southern stream is visible across the Southeast while the Northern Stream is diving through the Ohio Valley.

GOES-16 Low Level Water Vapor Loop (Image College of Dupage Weather Center)

The low will deepen as it moves north/northeast this evening. The progression at the surface from 1 PM today to 1 AM tonight

WPC Surface Analysis/Fronts Friday 1 PM to Saturday 1 AM

Impacts and Hazards

Snow begins to fall around midnight. Expect 3-6" by 7 AM. There is plenty of Arctic air available so snowfall ratios will be around 15-20-1, instead the standard 10-1 ratio. Watch temperatures fall from the low 20s to teens across interior Southern New England from 1 AM to 7 AM

12z NAM Hires 2 m temperature Sat 1 AM, Sat 7 AM (Image Weathermodels.com)

Temperatures are in the low 30's across Southeast MA, the Cape and Islands. This is concerning because the snow will be heavy and wet here. The Cape and Islands will also see stronger winds so the threat of power outages is substantial in these areas. The gradient will also help enhance snowfall rates to the west.

12z HRRR 10m winds Saturday 8 am to Sunday 12 AM (image WeatherModels.com)

I'd take these winds gusts with a grain of salt but they give a good approximation of the the timing and areas that will see the strongest wind. That said, it also shows that the chance for blizzard conditions in Worcester County is still alive (yay!)(yay?). 

Timing and Totals

Snow will wind down between 5-7 pm in Western and Central Southern New England. Snow may linger longer in Eastern MA. I still think most towns see 1-2 feet. I think Southern Worcester County will see 18-24", with 12-18 more likely across Western MA and even less into Berkshire County. I think 18-24 is also the best bet across Northeast MA and Rhode Island. I would expect the jackpot to be in Southeast Massachusetts where 24-36" will be the norm. 

NWS Boston Snowfall Forecast

I would take the 18-24 and extend it into Eastern CT but otherwise I think the National Weather Service snow map is a good one. One final note; there was some extreme snowfall totals showing up on some of the computer models. As a rule I try to avoid forecasting weather that has never happened before. But a few totals approaching 40" are possible if they sit under intense snow for several hours. 

Thanks for reading and look for some updates tomorrow. 

Major Winter Storm Coming Saturday

 The weather community was on a proverbial roller coaster ride this week. Some of the weather models produced an epic blizzard; others showed little to no snow. I wanted to post this blog last night but I was shook when I reviewed the data. 24 hours later things are much more clear and my reservations are mostly gone. In this blog I'll go over the weather headlines, the evolution of the storm, a timeline, and last but not least...a snowfall forecast. 

Weather Headlines

The National Weather Service Boston office (located in Norton) has issued a *Winter Storm Watch* from late Friday night through Saturday Evening 

NWS Boston Headlines 

These will be upgraded to Winter Storm or Blizzard Warnings tonight or tomorrow morning. This storm has the look of a textbook Southern New England blockbuster snowstorm. I'm going to nerd out for a minute to break down the genesis of the storm. If you only care about the when and how much, skip down a section. 

General Overview

To start, lets head up to ~18,000 feet to see what's going on at 500 mb

18z GFS 500 mb Height, Vorticity valid Thur 7 PM (image Tropical Tidbits)

You can see the shortwave in the southern stream moving through the Four Corners. The northern stream energy is more subtle but it is diving across the Dakotas toward Minnesota and Iowa. Perhaps you can pick it up better on the Mid-Level Water Vapor Loop (courtesy of College of Dupage Weather Center)

At the surface it looks like...not much of anything at all. There are some light snow showers in Colorado and a few flakes in South Dakota/Nebraska. 

18z GFS MSLP and Rain/Snow (Image Tropical Tidbits)

So how can something so tame turn into a blizzard? 

12z NAM 500 mb heights/vort (Image Tropical Tidbits)

The two shortwaves meet near the east coast as the southern and northern jet streams phase. Anytime you see a vorticity maximum at the base of a trough, as we see in the last frame of the GIF, meteorologists will look immediately to right front quadrant for a storm. When you get a phase of the jet stream, said storm is able to get very strong. Very strong storms produce more intense precipitation, stronger winds, and larger waves. There will be a very strong storm; so where will it track?

18z GFS MSLP and Radar Saturday 7 am to Sunday 2 am (image Tropical Tidbits)

The  American GFS is furthest south and east. Eastern MA would still get slammed but this would be more manageable in Central Massachusetts. I'll note that at the upper levels the GFS isn't all that different and has slowly nudged back west today. It still has plenty of wind and moisture and it bombs the low to 964 mb. 

18z ECMWF (Euro) MSLP/Precipitation Type valid Saturday 1 am to Sunday 1 am

We pick up the EURO at 1 AM Saturday. As you can see, its already snowing. The EURO is closer to the coast and also deepens the storm to around 964 mb. The EURO would be a blizzard for Eastern Connecticut, Rhode Island, Central and Eastern Massachusetts. I mentioned in the opening I was mostly confident. If the jet stream phase is late, or incomplete, the energy could move more east and shut out the Western parts of New England. 

18z NAM Hires Simulated Radar Saturday 1 AM-Sunday 1 AM (Image WeatherModels.com)

I think this is too far east, but it would be foolish to completely dismiss given the windshield wiper ways of the weather models with this storm.

Timeline

I will need to refine this but I leaning towards snow breaking out after midnight on Friday night, picking up in intensity by 8 AM. Snow will then fall, heavy at times, if not the entire time, until 7-8 PM when the intensity should begin to wind down. During this time, there will be some areas of enhanced precipitation. These places may see 2-4"/hr snowfall rates. Right now, I think the best chance of that happening is in Essex County on the North Shore and Plymouth County to the South Shore. We can't rule that out in Worcester County. That will be the focus of tomorrow's blog. The low pulls away around midnight and we are left to shovel on Sunday. 

Snowfall Totals

Most communities in Southeastern New England should prepare for 1-2 feet of snow. Yes, feet. I will make a more specific prediction tomorrow. I'll refine it to 12-18", 18-24", or perhaps...24"+. 

I'll leave you with the National Weather Service forecast. It's highly possible (probable) that several communities approach 3 feet. If the 2-4"/hr snowfall bands sit over any one area for a few hours, they will have a shot at 30". 

More tomorrow including a look at any coastal flooding and the winds. Thank you for reading!

Saturday Night Thoughts On Hurricane Henri

As expected, Henri strengthened into a hurricane today as it continues its journey northward towards Southern New England. A few things have come into focus today. The model trend of taking the storm west into New York City halted and corrected back east. Landfall is expected between the Hamptons on Eastern Long Island and Newport, RI. So far, Henri has not gotten appreciably stronger, until right around now. The pressure is down to 988 mb as of 730 PM. The window is closing fast; it has until around 10 or 11 PM tonight before the ocean fuel runs out.

GOES 16 Visible Satellite 3-530 PM (Image Credit- College of Dupage Weather Center)

As the sun is setting on Henri, look what is finally showing up on satellite- an eye! It also appears that thunderstorms are firing in and around that eye. Although expected, we would prefer to keep it on the weaker side. The IR satellite confirms this strengthening

GOES-16 IR Satellite 5-730 PM (Image Credit- Tropical Tidbits)

The hurricane hunters are en route to Henri as I write this (approx. 530 PM). This data will help confirm the strengthening trend and help provide valuable insights about the storm.  Its pretty remarkable that we were able to narrow down the landfall zone as quickly as we did, but because the severity of impacts from town to town vary depending on the exact track, we still want to pinpoint that final landfall location. 

12z FV3 3km Simulated Radar (Image Credit- WeatherModels.com)

I like this model because its new and also because it depicts the precipitation shield well. The eastern side of the storm will see very little precipitation. The heaviest rain will be across Western CT, Western MA, and Eastern New York State. Flash flood watches are never the less still posted in Worcester County. It won't take much rain to cause flash flooding and some of these outer bands from Henri can produce 1-2" per hour.   Less than an inch of rain is likely inside I-95 and less than 0.5 inch is likely across the outer Cape. 

National Weather Service Precipitation forecast (Image Credit- WeatherModels.com)

That said, a landfall in Southern Rhode Island would shift this map to east. There are several reliable models taking the storm into Narragansett Bay. This would be a worst cast scenario for Henri for Eastern MA and especially Central MA. 

NOTE- NOT A FORECAST, A POSSIBLE SCENARIO 

18z HWRF Sim Radar MSLP 2 PM Sunday (Image Credit- Tropical Tidbits)

Henri is not expected to have a large wind field and the winds aloft will be tropical storm force. During these bands of rain the strongest wind gusts will occur. Right now a general 40-50 MPH is expected in Central MA and Rhode Island. With the saturated soil, that should be enough to uproot trees and cause power outages. Unfortunately it looks like Connecticut will take the worst of Henri. Eversource is cautioning residents that power could be out for 8-21 Days (!) and that up to 1.3 million customers could lose power. 

But once again, shift this wind gust map to the east if the Rhode Island landfall verifies. 

National Weather Service Max Wind Gust (Image Credit- WeatherModels.com)

Several hundred thousand customers are expected to lose power. If you add in all of the Northeast it will probably top 1 Million.  The Storm Prediction Center has most of Southeastern New England (east of center) with a marginal risk of a tornado. 

To time it out, expect the first rain bands in Central and Eastern MA between 5-8 AM. The weather really goes downhill after 8 AM with the worst moving through between 11 AM-5 PM tomorrow afternoon. 

(Image Credit- National Hurricane Center)

Image Credit- National Hurricane Center)

This says some towns will see Tropical Storm force winds starting at 8 AM (top image) but the most likely time for them is after 2 PM (bottom image).

 In closing, Henri will be an impactful storm in Southern New England. Best wishes to your property and I'm hoping for 0 deaths. Tropical cyclones have a mind of their own. Be prepared for any scenario tomorrow and hope for the best.  I'll post as much as I can tomorrow. 

Henri Sets Its Sights On The Northeast US

Tropical Storm Henri is expected to strengthen into a Hurricane tonight or tomorrow before impacting the Northeast US with strong winds, flooding rain, and storm surge on Sunday. It may become the first Hurricane to make landfall in Long Island or Southern New England since Bob in 1991, but in reality there isn't much difference between a 70 MPH Tropical Storm and 75 MPH Hurricane. Ultimately, the exact forecast track will determine who sees flooding rain vs strong wind. In this blog I'll discuss the possible tracks and what kind of impacts that would have in Southeastern New England. 

National Hurricane Center Forecast Cone 

There is a Hurricane Watch and Storm Surge Warning for the Massachusetts (MA) South Coast, Cape and Islands and Rhode Island (RI) coasts and a Hurricane Warning and Storm Surge Warning for most of the CT and Long Island shorelines. 

Big Picture 

As of 5 PM Friday Evening, Henri is a 70 MPH Tropical Storm with a 994 minimum pressure. The storm has started its move to the North. Although convection remains impressive, the northerly shear is continuing to displace the center of the storm. If you look carefully at the visible satellite, you can see a swirl in top left of the storm. Until this co-locates under the deepest convection, the storm is going to have trouble getting stronger. 

GOES-16 Visible Satellite 4-6 PM (image credit- College of Dupage Weather Center)

The shear is expected to relax tonight and there are already signs of increased organization. Henri will be moving over the Gulf Stream, so intensification is likely as the storm moves northward. That heat starts to run out around 38 N, but it doesn't go away completely until 40 N. So the storm should begin to weaken as it approaches Southern New England and Long Island, but it won't have enough time to lose all its strength.

Tropical Cyclone Heat Potential (image credit- WeatherModels.com)

Henri is expect to move slowly, which is unusual for a Northeast tropical cyclone. The legendary Hurricane of 1938 was moving close to 50 MPH. That is why I am skeptical that Henri breaks the 30 year Hurricane drought, but it won't really matter. This storm will have a high impact on millions of people. The slow movement gives it more time to weaken, but it also allows for more rain. I don't need to tell anyone in Southern New England just how unwelcome that is. 

National Weather Service Flash Flood Guidance for 3 Hour Precip (Image Credit- WeatherModels.com)

This map says that it will only take 1.9 inches of rain in 3 hours for flash flooding to occur in Worcester. It will take 3 inches in Springfield and 2.1 inches in Boston. Tropical cyclones produce tremendous rainfall as we have seen locally with Elsa and Fred already this summer. The Weather Prediction Center is highlighting a slight to moderate risk of flash flooding across SNE on Sunday and Monday. Flash flooding can literally happen in a minutes (flash)- for reference see what happened on Route 20 in Worcester yesterday. Water started to rise rapidly, stranding several motorists.  Turn around, don't drown!

It can also cause ordinarily calm streams to rise rapidly so please consider creating an evacuation plan in the event that your local stream decides to go crazy. Unfortunately, that happened in Western North Carolina as Fred moved through this week. As of today, there are at least 4 confirmed dead and at least 20 more missing.

WPC Excessive Rainfall outlook (source)

Soggy ground makes healthy trees susceptible to strong winds. Normally 50-60 MPH does not get the attention of New Englanders. 50-60 MPH cold season winds out of the NW do not generally cause damage to healthy trees. Sure, rotted trees and some branches come down but its not generally a big deal. Southeast winds on the other hand are trouble makers in Southern New England. Add in the moist soil and uprooted trees is a big concern with any winds over 40 MPH. Eversource is estimated 300-600K outages for an Eastern CT landfall and over a 1 million if it makes landfall in Western CT. That doesn't include National Grid so you can imagine the potential for long service disruptions. 

The other concern will be storm surge flooding. There is an astronomical high tide this weekend, which will enhance the threat. Add waves on top of the surge  along the South Coast of MA, RI, CT, both sides of Long Island, New York City, and the Jersey Shore and there will be moderate to major coastal flooding. 

National Hurricane Center Peak Surge (source)

Scenario's In Southern New England 

As currently forecasted, Henri would make landfall in Long Island and South Central Connecticut before moving into Western Massachusetts. That track would bring 6-10 inches of rain to parts of CT and W MA. A general 1-3" would fall in Worcester County with even less in Eastern MA. All of that rain could potentially come in 1-2 bands, so flash flooding would still be possible, but the odds of it occurring would decrease across Central and Eastern MA.  These bands would also be capable of producing tornadoes. There were 2 confirmed tornadoes in the area yesterday as Fred moved through.  They tend to be brief, but can cause localized destruction, similar to the twisters that moved through Douglas, Uxbridge, Northbridge, and Upton in 2018. 

Weather Prediction Center Forecast Precipitation though Wednesday 8/25 (source)

The trade off would be stronger and more frequent damaging wind gusts. This track would lead to widespread tree and power line damage in Central MA with scattered tree and power line damage in Greater Boston. This track would largely spare the Merrimack Valley, Eastern NH and Maine. It would be similar to Hurricane Irene from late August 2011. Irene weakened to a Tropical Storm but it still knocked out power to millions in the Northeast. Irene caused tremendous flooding and was also a slow moving Northeast Tropical Cyclone. A lot of people are comparing this to Hurricane Sandy's left hook turn, but Irene is a stronger comparison.

Another potential outcome for Worcester County would be a landfall around Montauk to New London, CT, gradually bending west through Hartford to Springfield. This would bring stronger wind AND heavier rain to Providence and Worcester plus more coastal flooding in Buzzards Bay/Cape and Islands.  There is some computer model support for this scenario

NOTE- IMAGE NOT A FORECAST

18z HWRF HENRI Composite Reflectivity Sunday 4 PM (Image Credit- Tropical Tidbits)

The next question is how strong will it be when it gets here. I think at best, it will be a low end Category 1 Hurricane. If it really blows up tomorrow, maybe the storm would be at 80 MPH at landfall. On the other hand, at worst I see it coming in with 60 MPH winds. I'm taking 70 MPH. 

Timing

We have all day Saturday to prepare, although I do expect some showers and thunderstorms tomorrow. The atmosphere will feel noticeably tropical. The first bands will arrive well ahead of the storm early Sunday AM. The first impactful bands will approach the Providence, Boston, and Worcester corridor after 5 AM and the significant bands moving in after 7 AM.  The worst of the storm will be mid afternoon as the center, perhaps eye? of Henri makes its closest pass to Central and Eastern MA. Precip will pause in Central and Eastern MA around 8 PM  as the center slowly drifts into the Berkshires, where the rainfall "jackpot" will be. 

Some guidance is insisting that the low will loop around and trigger additional rainfall on Monday. We will have a better handle on that tomorrow.

Conclusion

My advice is to prepare for power to be out for 1 week. Not everyone will lose power for one week, but some people will. If you live near the coast or by a river, have an evacuation plan. Storms like this are rare in the Northeast and its best to prepare for the worst and hope for the best. Mother Nature did not do us any favors this summer and a tropical system is the last thing we needed.  More details tomorrow. Have a good night and thanks for reading. 

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

Biggest Snow Storm Of The Season Heads To Impact Region Tonight

The National Weather Service (NWS) in Norton, MA has issued a *Winter Storm Warning* from 7 PM tonight until 10 AM Wednesday.  A widespread 6-10" snowfall is expected.  This storm will be the biggest of the season in Boston, surpassing the 3.6" on February 18.  November 15, 2018, is the high snow mark for Worcester and Providence so far this season.  7.8" fell in Worcester while 6" fell in Providence.  Both of those records should fall tonight/tomorrow morning, though Providence is more of a lock than Worcester. 

NWS Early Sunday PM Headlines

I've had a lot of questions from inquiring minds wondering what the deal is with this storm.  Let's answer in those in a Questions and Answers blog.

It's pretty nice this afternoon.  Is it really going to snow?
Partly to mostly cloudy skies will give way to all clouds later this afternoon, but before that happens, a few breaks of sun will help keep temperatures in the upper 30's and low 40's.   However, they will fall into the upper 20's and low 30's this evening.  It is not a classic "noreaster" set up because there is no cold Canadian high pressure to our north supplying the region with a fresh supply of Arctic air.  The first few hours of snow will fall with temperatures near freezing so expect so wet flakes to start.  By 1 AM, Worcester County will be in the upper 20's.  So it won't be a powder bomb like Thursday morning, but it also won't be a heavy wet "spring" snow either. 

What is the storm doing right now?
The storm is currently dropping snow across Missouri, Illinois, Indiana, Ohio, and Pennsylvania.  The south is seeing heavy rainfall and severe weather. 

WSI/Wunderground Intellicast National Radar 1215 PM
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The presentation on satellite is also impressive.  It is still in the process of maturing, but it is going to have the classic "leaf" or "comma head" by the time it is moving past Southern New England.

NOAA GOES EAST (16) Continental US IR Satellite 

At the surface, we see strong high pressure descending into the Upper Midwest and into the Great Plains.  The radar confirms the amount of precipitation available as this surface low works across the Southeast and starts to re-develop off the Mid-Atlantic coast.  

WPC Surface Fronts/Precipitation Sunday 1 PM

Okay cool, but when does it start?

Snow will begin to fall in Southwest Connecticut after 5 PM and will get into Worcester in Boston around 7 PM (give or take).  

16z HRRR Simulated Radar Sunday 5 to 9 PM (image WeatherModels.com)

As mentioned before, temperatures will be falling into the upper 20's in Northeast MA and Worcester County, so expect this to start sticking to untreated roads right away.  

When will the heaviest snow occur?

Expect snow to fall at moderate to heavy from 1 AM until 7 or 8 AM in Central Massachusetts, and until 10 AM in Eastern MA.  The majority of snow accumulation will fall during this time period and travel will be extremely difficult.  The low will deepen as it moves from the Mid-Atlantic coast to just Southeast of Nantucket. 

WPC Surface Fronts/Precipitation Monday 1 AM, 7 AM

I think 1-2"/hour snow rates are possible as the low gains strength and slides to our southeast.  This is likely in the region bounded by Boston, Worcester, Hartford, Providence, and Plymouth.  The most likely time for these intense rates would be 2-5 AM.  

16z HRRR Simulated Radar Sunday 9 PM to Monday 5 AM (image WeatherModels.com)

I see a sleet line in that radar loop.  Will I get all snow?

Almost everyone away from the Cape and Islands will see all snow.  Sleet will mix in up to Hartford-Providence-Plymouth line we just discussed.  

How much snow?

A general 6-10 inches.  The NWS is calling for 6-8" for almost all of the region.  Some of the higher resolution models are going for 8-12".  A few communities will see over 10" but I believe they will be the exception.  I do think a lot of towns come in around 7-9" so for insurance, 6-10" for all regions except those that mix with rain and sleet.  

NWS Snowfall forecast through Monday 1 PM (image WeatherModels.com)

What about the Monday morning commute?

Snow will still be falling at 7 AM in Central and Eastern MA and Rhode Island.  It will ease up by 10 AM.  With the bulk of the snow falling just before the commute, I expect a horrendous morning on the roads for those who have to be on them.

Will there be school?

I think most schools will close.  

Any further questions?

Leave in the comments on the Facebook page or @zgreenwx on twitter.  

-Zack Green