Friday, March 10th, 2017 Snow Event

Our stint of mild weather will be short-lived as winter weather is set to return to the state, both in terms of potential snowfall and very cold temperatures.  Overnight tomorrow into Friday morning a rather potent piece of shortwave energy and associated trough will dig just to the south of CT.  In response an area of surface low pressure will develop and strengthen with the aid of a rather impressive 120+ knot mid-level jet streak rounding the base of the trough.  There are some questions, however, as to whether or not the trough (as it digs south of CT) will capture the developing area of surface low pressure and allow it to strengthen rather quickly.  This sort of scenario would increase snowfall total potential across the state:

At this time we are still faced with several questions which makes this forecast rather difficult.  It isn't exactly clear how this system will evolve as there is a solid difference (for this time range) in spread between the computer forecast models.  Computer forecast models have been wobbling back and forth with regards to exactly how far north the system would track and they have been inconsistent as well with regards to whether or not the amplifying trough will capture the surface low in time to allow for heavy snow and upwards of several inches of snowfall accumulation across the state and there have been some questions with regards to whether or not there will be sufficient inflow into the system to generate across moisture for the system to work with.  All of these factors will determine how strong of a system this is and exactly how much snow will fall.

At this time, however, there are some signals that we could be looking at a greater potential for more in the way of a stronger system as opposed to a weaker system.  The first signal is what was discussed above with regards to whether or not the trough would capture the surface low.  Given how models do agree on amplification on the trough as it approaches our area it is a bit difficult to believe it would not capture the surface low and allow for an extended period of at least moderate snows across the state:

Another signal for at least a narrow zone of rather heavy snowfall is a very impressive baroclinic zone (tight temperature gradient = rapid change of temperature over a short distance) in the lowest 10,000' of the atmosphere.  What this will do is help to generate a zone of very intense upward vertical motion which would indicate a narrow zone of heavy snowfall.  It is within this zone the highest totals would occur:

Taking a look at bufkit profile for Waterbury, CT from the latest runs of the NAM and GFS computer forecast models, we see both models showing rather decent snow growth with the dendritic snowgrowtyh zone up around 12,000' to 15,000' along with the -15C isotherm bisecting this zone and a good deal of upward vertical motion (indicated by the red contours)...all of these are ingredients you want for "good" snow growth within the clouds...this is what gives those big fluffy flakes which accumulate.  The degree of upward vertical motion as well indicates the potential for at least a period of moderate to perhaps even heavy snows:

What can we expect?

The timing of the snow should be during the overnight hours of Thursday into Friday lasting until mid-morning or so, later if what was mentioned above with regards to the trough capturing the surface low.  Snow should begin to break out as early as 12:00 AM or so.  The heaviest of the snows should occur between about 1:00 AM and 6:00 AM but this is low confidence given what was described above and may last longer.   Surface temperatures will be rather marginal, especially across southeastern CT, however, temperatures aloft will be cold enough to support generally all snow, especially considering the timing is at night.  SE CT could see a mix which could hold totals down a bit there.  Once the snow does clear out a strong cold front passes through and we turn windy and much colder for the rest of the weekend.  Below is what I am expecting right now: