Potent Storm System To Bring Region Wide Impacts Saturday Through Sunday

A clipper system diving southeast out of Canada is going to rapidly intensify into a very powerful storm just off the coast.  This system will be will bring a slew of impacts to southern New England including; moderate to heavy snowfall, the potential for very strong damaging winds, brutally cold temperatures, and dangerous wind chills.  All the latest trends indicate that the potential for the highest snowfall amounts will be confined to eastern MA once again.  This system is expected to have significant impacts and we will break everything down.  First, we will take a brief look into the setup:

Brief Meteorological Look

An innocent clipper system will be tracking southeast from central Canada and move right over southern New England.  As this clipper system moves off-shore, rapid cyclogenesis (strengthening) is expected to occur.  As the system begins to rapidly intensify, moisture will get drawn into the system and this will eventually lead to snowfall breaking out across the region.  In response to the system rapidly strengthening, this will increase the pressure gradient across the region and this will yield to very strong to perhaps damaging winds developing, especially across eastern MA and the Cape area.  With the wind component mainly from the north and northeast, this will reinforce brutal Arctic cold into the region with temperatures mainly in the single digits and teens throughout the duration of the storm.  This coupled with the potential for very strong winds will yield to some dangerous wind chill values.

We will now do a breakdown of each associated hazard expected with this system and what we can expect with each associated hazard:

Snow

We will first look at the snowfall potential associated with this system.  This will be an all snow event...no worries about any sleet, freezing rain, or rain mixing in as temperatures throughout the atmospheric column are more than supportive for snow.  One thing with this system is, the precipitation really doesn't get cranking until the system is strengthening off-shore.  This will lead to reduced snowfall totals the further west you go, however, the further east you go, this could yield to some significant snowfall accumulations (>12'').

During the day on Saturday we will see periods of light snow region wide, these snows will be associated with the clipper as it moves overhead towards the coast.  Snowfall accumulations during the afternoon hours should be on the light side, perhaps a few inches in spots but the periods of heavier snow don't begin until we near the evening hours.

As we approach the evening hours and the clipper and energy aloft associated with the clipper begin to move off-shore, the strengthening process will rapidly begin to occur.  As this happens stronger lift will develop across the region and more moisture will work into the system.  This is when we will begin to see periods of moderate to heavier snowfall break out across some spots.

Due to the fact that this system will be strengthening off to our east instead of off to our southwest, this means the majority of the heaviest snows will be on the backside of the system associated with what is called the cold-conveyor belt (or CCB).  It is this which will be key as to where the heaviest snowfall sets-up and where the highest snowfall totals occur.  The big question with regards to the CCB is when does it begin to develop and take shape.  This is something that needs to be watched, especially for CT and central MA as if this develops later as opposed to earlier it will mean reduced snowfall totals, however, if it develops earlier, that would lead to increased snowfall totals so this will be closely monitored over the next 24-hours.

We are looking at the time period from late overnight Saturday (roughly 2-3 AM) through late morning to about noon time on Sunday as the timeframe for the heaviest snows to occur.  Across western and central MA down to western and central CT, snows should begin to taper off mid-Sunday AM.

Under the heaviest banding of snows, snowfall rates could approach as much as 4-5''/HR but this will not be the norm region wide...these totals will only be confined to the heaviest banding and where thundersnow is possible which is more likely to occur out across eastern MA.  Elsewhere expect snowfall rates of up to 1''/HR at times.

Here are my initial snowfall projections but this will be further fine tuned tomorrow:

Wind

Wind will be a major issue with this system, especially out across eastern MA thanks to a very tight pressure gradient that will be in place with the near 970mb low just to our east.  The combination of very strong winds and snow will yield to blizzard conditions at times, especially out across eastern MA and will also lead to very dangerous wind chill values.  Winds out across eastern MA towards the Cape could gust upwards of 70-80 mph!  These are gusts which will rival category 1 hurricane strength and would lead to widespread power outages along with big time drifting blowing and drifting of snow.  As you move further west across southern New England the magnitude of the winds won't be as severe, however, we are still looking at winds gusting potentially upwards of 65 mph.  These values are still strong enough to yield scattered power outages along with blowing and drifting snow.  We will actually see winds becoming gusty during the day today and continue right through Monday with the peak intensity of the winds from tomorrow night through much of Sunday.  If the higher end of these values are realized across eastern MA not only would we be looking at widespread power outages but outages lasting several days or longer.  Here is a map showing the potential wind gusts:

 
Temperatures

Temperatures will be down right COLD.  We are only looking at temperatures to be in the single digits to perhaps the low teens throughout the duration of this event as brutally cold Arctic air is transported southward thanks to strong northerly to northeasterly winds.

Wind Chill Values

The combination of temperatures only in the single digits to perhaps low teens and winds sustained between 20-30 mph (higher further east) with potential for gusts 60+ mph will yield very dangerous values at times.  We could see wind chills range anywhere from -15F to as low as -25F during the storm.  Those are very dangerous values and pose a high risk for frostbite in a very short amount of time.  It is this reason, along with the accumulating snows that travel should not be done unless absolutely necessary.  If you are out traveling and get caught this will pose a life threatening situation given the degree of cold we are dealing with.  

Snow...Snow...And More Snow

     The weather pattern over the next several days looks to remain quite active as multiple pieces of energy moving through the jet stream aloft will yield the potential for not only snow every day between tomorrow and Tuesday but the potential for accumulating snows each and every day.  It is EXTREMELY IMPORTANT to note that it will not be snowing this entire time and not everyone may see accumulating snows or even snow each and every single day.  This is quite the complex situation and while this will be quite a lengthy post, this post will go into great depth and detail regarding what to expect and what we are looking at.

     Below is a graphic displaying 1000mb to 850mb thicknesses.  I have highlighted several key areas which will be of extreme importance as we move through the weekend and into the beginning of the work week.  The explanation of the highlighted areas and their importance will be discussed below the image:

     The red circled areas are areas of high pressure.  Notice how there is a big area of high pressure just to the north of the United States across central Canada and a huge area of high pressure across the southern portion of the United States.  In between these areas of high pressure we have our frontal boundary, an Arctic cold front and this, along with the area of high pressure across Canada is allowing for brutal Arctic cold to work here in to New England and the flow around the high pressure is allowing for this cold to be maintained.  The area of high pressure across the southern-tier of the United States is allowing for this front to stall across the extreme northern-tier of the country and just south of New England.

     The blue circled area is where not only our frontal boundary is positioned but this is where the mid-level jet stream is located as well (although not pictured here).  Notice the green shadings within this circled zone?  This is moisture associated with the boundary and this moisture is streaming across this portion of the country all the way from the Pacific!  As long long as this pattern configuration is in place Pacific moisture will continue being streamed all the way here into New England.  As we eventually move into Sunday the pattern will also begin to allow more in the way of Atlantic moisture to work into the picture as well and this is when some areas could receive some significant snows.  What our focus will be on over these next several days is pieces of energy developing and riding along the stalled out boundary in this highlighted area.  Lift + moisture = precipitation and we will have plenty of moisture to work with so add in any extra lift and we will be looking at the potential for quite a bit of precipitation...but the million dollar question is, where will the axis of highest amounts occur?  

     Now we will take a look at each of the upcoming days with a bit of detail and what we could potentially expect.

Saturday

     For the most part, Saturday and Saturday night is looking to be the "quieter" of the days between tomorrow and Tuesday.  Computer forecast models bring a weak piece of energy through the jet stream tomorrow and have some light moisture associated with the energy.  As of right now it appears the track of this system will be more through central and northern New England, meaning the highest degree of lift will be across these areas.  If this track verifies it will be areas north of the MA Pike up through central VT, central NH and into southern ME which see the periods of the heavier snows.  Across these areas 1-3'' of snow will certainly be possible within this area.

     South of the MA pike across southern MA into CT and RI, the degree of lift is not expected to be as strong with this track so these areas should remain outside of the heavier snows.  Still, some locations may pick up an inch or so of snow, especially across the higher terrain.  

Sunday

     As we move into the overnight hours of Saturday into Sunday, this is when things will begin becoming more interesting.  By this time more in the way of Pacific moisture will have spread into the region and computer forecast models are hinting at some stronger pieces of energy moving through aloft.  Higher moisture content and stronger lift indicate periods of moderate to heavy snows will become much more common overnight Saturday through much of the day on Sunday.  While it will not be snowing this entire time everywhere, we will see multiple periods of moderate to heavy snows throughout this time.  We will not be seeing a widespread precipitation shield which encompasses a large area (like we see with coastal storms), rather we will see numerous bands of snowfall which will likely be more narrow in nature.  This means that you can have an area where snow is coming down extremely heavy, however, you go just several miles away and nothing is occurring.  It is a situation like this which will make forecasting snowfall totals EXTREMELY difficult.  Between overnight Saturday into the overnight hours of Sunday some of the hardest hit areas could receive as much as 6-10'' of snowfall and perhaps even some higher amounts in some spots.  On the other hand, areas who don't see much action may be luck to get 2-4'' and the axis between these high and low amounts could end up being only a matter of miles!

Monday

     Moving overnight Sunday into Monday this is where the forecast becomes even more complex and that is because we are still a little far out.  However, computer forecast models develop a stronger area of low pressure right along the stalled out front.  This is where we will begin to see more in the way of Atlantic moisture become involved as well and this is when we could see even higher snowfall totals.  The track of this low and the strongest lift and moisture will all depend on the exact positioning of the stalled out boundary.  This is something which will be sorted out over the next 24-48 hours.  With this system we may also be looking at a more widespread precipitation shield meaning a much more widespread area is hit harder...as opposed to only a few select locations.  This system will have the potential to yield upwards of 9-15'' of snow with lesser amounts of 3-6'' across the areas outside of the heaviest precipitation.  This portion of the forecast though is much more tricky at this time.  

Summary

     Between tomorrow and Tuesday it is not out of the question that some spots could pick up anywhere from 12'' to even 20'' of snowfall depending on how everything aligns and comes together.  Just keep in mind this is not going to be a uniform system where we are looking at uniform totals across a widespread area.  The difference of even 5-7 miles could be the difference between 6''+ of snowfall totals.  This can't be stressed enough.  With this in mind, I feel creating a snowfall map is not the right thing to do at this time as amounts may vary widely across such a small area.  

How to Prepare?

     Just keep listening to all forecasts and all the updates provided.  Just keep in mind that on the higher end of the scale you could see as much as a foot-and-a-half of snow and on the lower end you may only see a half-a-foot of snow.  Always prepare for what the higher end of the scale may bring as it's better to be over-prepared than under-prepared.  

Beyond Tuesday

     Looking ahead to the end of the week and next weekend we could be looking at some of the coldest temperatures we have seen in quite some time as computer forecast models indicate Arctic air plunging directly into New England but we will worry about this as we get closer.