First Widespread Snowfall of the Season Sunday into Monday?

We have entered a very active weather pattern and this will continue at least through the next week and our next chance for a weather maker comes Sunday night into Monday as our computer forecast models have become in stronger agreement for a storm system to impact southern New England Sunday night into Monday.  This system could also produce the first widespread snowfall of the season, however, we may also have to deal with the transition to sleet, freezing rain, and even rain.  It is still a bit too early to get into further details at this point but we can highlight some of the possibilities and the potential setup.

Embedded in a rather fast/zonal jet stream will be a piece of shortwave energy.  Given how the flow is more zonal/fast this leaves very little room for amplification (the system will not dig and work towards the coast), however, there will be just enough small-scale amplification for the system to strengthen and spawn an area of surface low pressure:

The expected track of this storm is likely to our north and west which typically means either a rainy solution or snow changing over to rain.  However, in this situation we will have a pretty cold airmass in place across the region both at the surface and in the lower-levels of the atmosphere.  With the storm tracking to our north and west this would eventually shift winds in the lower levels of the atmosphere to a more southerly or even southwesterly direction which would usher in warmer air eventually and allow for snow to transition to rain.  Computer forecast models show the system strengthening rather rapidly as it ingests a great deal of moisture from the Atlantic Ocean.  There is a possibility that the system strengthens so rapidly that it actually begins to occlude.  This could lead to a few things; 1) When systems occlude this shuts off the inflow of warm/moist air into the system which is needed for systems to maintain their strength or even intensify.  With this they eventually begin to weaken.  2) The early occlusion would actually prevent the warm front from pushing northward and in this situation that could mean the warm front stays to the south of CT.  This doesn't necessarily mean we don't see warming but the degree of warming could be very weak, especially at the surface.  The surface though is not the only area of concern for warming temperatures but it will be a concern for the lowest several thousand feet of the atmosphere.  With the system strengthening computer forecast models suggest the system could develop closed off low pressure centers at 925mb, 850mb, and 700mb with these lows tracking to our north and west as well.  This would surely advect in a good deal of warmth in the lowest several thousand feet of the atmosphere so even if the surface remained cold enough we would see snow transition to sleet or even freezing rain:

At this point there are still a quite a bit of uncertainties with regards to how the storm evolves, how much snow we see, and when the transition period occurs from snow over to rain and how much sleet or freezing rain we may see.  These are all details which can be ironed out over the weekend.  There are some things, however, which need to be considered with forecasting this system;

1) Very warm ocean temperatures:  Temperatures off the coast are much above-average and this will work to not only enhance the storm but supply a great deal of moisture into the storm.

2) The possibility for an area of high pressure to slide off the coast of Maine:  This would be a HUGE focal point because the flow around the high pressure would establish a more northeasterly flow into our area and that is something that could help keep colder air locked in the surface much longer.  While this wouldn't halt warm air advection aloft, this could allow for a higher likelihood for sleet or even freezing rain so this is something that needs to be watched.

3) Intense lift:  With the surface warm front perhaps stalling off-shore and moisture being thrown up and over the front into the system this could allow for a several-plus hour period of rather heavy precipitation (whether it be snow, sleet, freezing rain, or rain).

Regardless confidence in some major impacts are increasing, especially considering the timing of the storm which could be for the morning rush commute on Monday and perhaps even afternoon commute as well so travel may certainly be impacted.

As we get closer to the event and details become much more clear we can start getting into potential snowfall totals and who exactly changes over from snow and how significant any impacts from sleet or freezing rain may be.