One thing that is a bit uncertain at this time is the exact track this system will take and this holds true for the surface low as well as low pressure centers aloft as well. If the surface low tracks further west and passes just southeast of CT this could allow for some milder air to work into portions of the state introducing the potential for mixed precipitation (sleet, freezing rain, rain). A track just southeast of this position allows for colder air to remain in place and the likelihood for any mixing is extremely low. As for the low pressure centers aloft, some guidance has suggested that the lows at 850mb and 700mb could track over or even just west of CT. This track for the 850mb low would bring in warmer air up around 5,000' and increase the likelihood for mixed precipitation across portions of the state and this track for the 700mb low would actually allow for some drier air to work in around 10,000' and reduce snowfall intensity and rates. If you're looking for lots of snow from this event you want all these lows to track just to the southeast of CT.
With this system becoming so strong there will be rather exceptional upward vertical motion which develops on the northwestern side of the low. This will really work to enhance the development of snow and allow for a period of extremely heavy snowfall in which snowfall rates could approach 2-3'' per hour and even some 4'' per hour rates can't be ruled out. The black and gray shadings of 800-600mb averaged frontogenesis suggest exceptional lift will push over a portion of the state on Tuesday:
Looking at bufkit profiles from this morning's run of the GFS computer forecast model for Waterbury, CT and Windsor Locks, CT we can also see the rather intense upward vertical motion as the GFS indicates as much as -40 to -50 units of omega within the dendritic snow growth zone! This is very impressive and hints at the potential for those snowfall rates to approach 3'' per hour where the heaviest banding sets up:
The cards are certainly right on the table for a rather major/significant storm but the question is just how significant? Well there are some factors we will be dealing with which could prevent this from being a situation where we are looking at 12-18'+ statewide. One factor will be the speed of the storm. It's not exactly a quick hitting storm (will last a solid 9-12 hours or so) but its not a very slow moving system and that will prevent the likelihood for any extreme snowfall totals (say several locations picking up 24"+ of snow). If this was a longer duration storm the cards would be on the table for a swatch of 20-30'' of snow.
There is also some concern of some drier air which may sink into the middle and even lower levels of the atmosphere as the storm progresses and this shows up well on some forecast soundings. For example, we will look at a sounding from the NAM computer forecast model for Waterbury, CT for 2:00 PM Tuesday afternoon. Those three blue circles on the bottom left indicate that moderate to heavy snow will be falling. However, if we look at the profile of the atmosphere we see a quite a bit of dry air (the further spaced apart the red (temperature line) line and green (dewpoint line) the drier the air is at that level):
What would this mean? If the degree of dry air does indeed verify this could impact the snowfall rates in a way where the intensity is on the lighter side and the snow growth may not be all that stellar (smaller-sized flakes). This will have to be watched to see if 1) We do indeed see drier air filter in and 2) If so, how quickly does that happen as this could really affect snowfall totals.
Another potential issue is subsidence (sinking motion which reduces intensity of precipitation or prevents it from reaching the ground) in and around the 850mb level (~5,000'). While there is no question with regards to the strength of upward vertical motion at 700mb (~10,000') this subsidence in the lower levels would likely reduce the intensity of the snowfall along with the snowfall rates. Given the nature of this storm and how intense it will be there is guaranteed to be a zone of subsidence that sets up somewhere, it's just a question of where and that is not something that is very easy to forecast days out:
Winds with this system are expected to be rather strong as well and this is not good to keep big fluffy snowflakes intact as they fall towards the surface. With winds both aloft and at the surface expected to be very strong, this could lead to snowflakes being ripped apart as they descend towards the ground. This would yield smaller flakes and ones that are tougher to accumulate quickly as opposed to those bigger fluffier snowflakes. These are a few things to take into account when making this forecast and to closely monitor over the next few days.
What can we expect?
- Snow begins to break out between 3 AM and 5 AM Tuesday morning and begin to quickly pickup in intensity.
- The heaviest of the snowfall occurs between 9:00 AM and 1:00 PM. This is also the time when the heaviest banding will setup somewhere within the state and this is where snowfall rates could approach 3'' per hour and perhaps even upwards of 4'' per hour.
- Given the timing of this system travel is not advised Tuesday morning. Unlike with what happened Friday, the ground this time is much colder and we are looking at heavier snowfall rates and longer duration so the snow will stick to the roads.
- Winds will become an issue as well as winds will be sustained between 20-30 mph with gusts upwards of 50-60 mph, especially down by the coast. This will cause pockets of power outages and downed trees
- The storm begins ti push out during the early afternoon hours with some light snows sticking around into early evening.
- Don't be shocked either if you hear some thunder given the degree of lift associated with the system
Before we get to the map just want to point something out with regards to that zone of 12-20'' totals. Yes that is a rather big range, however, as the details with the banding become much more clear that range can be narrowed down. Also this axis could shift as well depending on where the banding setsup and that is very, very difficult to pin down at this stage. Based on some of the questions mentioned above, I think a widespread 8-12'' can be expected across the state, however, totals will be much higher in that area of banding. There will also be an area of perhaps less than 8'' where the subsidence zone setusup:
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