Accumulating Snow Still on Track

For meteorologists and anyone who forecasts weather these past weeks have been hell. It is situations like this where I always wish the general public had an idea of why forecasting the weather is so difficult and the process involved in constructing weather forecasts. This is sort of the reason why I construct my posts to be so technical and show so many images. My hope is that the reader gets a little insight into the background behind forecasting.

The past 24 hours...even 36 hours has been an absolute nightmare. Forecast models have been all over the place, wavering back-and-forth between solutions and there has been terrible disagreement between forecast models. Typically when we get into the nowcasting aspect of forecasting (typically that's when you're within about 6 to maybe 12 hours out, things become much more clear because you can see how things will unfold as they're happening...well this still isn't really the case with this system. Why is that?

This system was incredibly complex with multiple pieces of energy moving through the atmosphere. The greater the amount of energies at play, the more complex the situation becomes and it becomes more difficult for forecast models to handle them and how they will evolve. Providing a comparison, think of it as solving a puzzle. When you have a puzzle that has 20...30...40 pieces, the puzzle isn't all that difficult to solve, however, when you have a puzzle that has maybe 1500+ pieces, well it becomes much more difficult to solve the puzzle easily because you have more pieces to work with.

Let's look at some of the inconsistencies the forecast models are still having with this system and what we can expect across Connecticut. We will look at total liquid precipitation accumulation by the NAM forecast model, the GFS forecast model, and the HRRR forecast model through 5:00 AM Thursday morning:

Look at these differences! The HRRR has less than 0.50'' of total precipitation accumulation for the majority of the state while the NAM has generally greater than 0.60'' across the majority of the state and the GFS generally o.30'' to 0.60'' across much of the state with more towards the east. This is just one of the many tools used when forecasting snowfall. On average, 1'' of liquid will equate to about 8-10'' of snowfall. This is an average, however, and can vary based on numerous atmospheric processes including. In the situation with this storm the idea was 1'' of liquid would equate to as much as 10-12'' of snowfall. Seeing these extreme differences in liquid precipitation make this rather challenging to figure out just exactly how much we see. Another issues is the very tight gradient some models, including the European model have in terms of liquid precipitation across the state (with more in the south and a sharp cutoff as you get towards Hartford and points north).

Here is a radar grab from 1:12 PM this afternoon:

 This shows moderate to heavy snows off to our southwest across portions of Pennsylvania, New Jersey and farther south into the mid-Atlantic. While the radar does suggest snow over Connecticut we are dealing with a great deal of dry air within the lower portion of the atmosphere. Until this dry air saturates (becomes more moist) it is going to be very difficult for the snow to reach the ground with the exception of extreme southern Connecticut. The degree of dry air also complicates snowfall forecasts because there are some indications the dry air hangs around for a very long-time across the northern part of the state which would only increase the gradient in snowfall totals from north to south. This bufkit sounding from this morning's run of the NAM forecast model for Windsor Locks, CT at 2:00 PM this afternoon shows the abundance of dry air. Notice how far apart the red line (temperature) and green line (dew point) are? The more spread apart, the drier the air. Forecast models, however, do bring these closer together as we head into the evening indicating moistening of the atmospheric profile:

How is the storm shaping now? The storm is really beginning to take shape and strengthening just off the coast of the mid-Atlantic. This strengthening will continue to occur as the afternoon progresses. This is evident by a tightly closed off circulation developing at 700mb and 500mb just east of Virginia by this evening. As these circulations close off and become more tightly closed (this is indicative by the increased number of "circles" with smaller diameters) this is a tell tale sign of a very strong system:

The big challenge we are still faced with is how far northward can this system push and whether dry air over the northern portion of the state can become more saturated? Forecast models do suggest we will see a band of heavier snow push into the state but not until late afternoon or not even until the evening. From here the question becomes how heavy this band of snow is, how intense the snowfall rates are, how long the band sits, and how far north this band works into Connecticut? So many questions yet to be answered.

Currently the surface low sits east of Delaware where it has been for the past several-plus hours. As the mid-levels further strengthen (which we looked at in the above image) the surface low will continue to strengthen and it will begin to move off to the north and east:

Forecast models still are uncertain with regards to just how much lift we will see in the dendritic snow growth zone and that too complicates snowfall forecasts. Let's again look at Windsor Locks, CT. The 3 km NAM shows a period of extreme upward vertical motion within the dendritic snow growth zone over Windsor Locks, CT later tonight. This would indicate a period of very heavy snowfall. The 12 km NAM is much less robust with the degree of upward vertical motion within the dendritic snow growth zone as is the GFS. Forecast models, however, are more robust across the southern portion of the state:

What should we expect through the rest of the day? Outside of the immediate shoreline we will not see a great deal of snow during the afternoon hours. The air is still very dry and will take some time to saturate and the bulk of the storm is still well off to the south. As we approach late afternoon and early evening, all indications are that the atmospheric column will saturate and as heavier precipitation works into the state we will begin to see snow fall. The heaviest of the snows will occur during the evening hours and lasting into the overnight hours. There is still some uncertainties with regards to how late the snow will persist but there is a possibility it could persist late enough to where the morning commute will be rather messy...messy due to clean-up efforts. Based on the shift with the storm winds should be be as big of an issue as though as we are looking at gusts more in the 35-45 mph range. There could still be some isolated power outages, especially across the immediate shoreline. The worst of this storm will be this evening into overnight. Given everything mentioned above here is the updated snowfall map:

Note: There is a good probability that most locations end up with snowfall totals towards the lower end of these ranges as opposed to the higher end of the ranges. If heavier snowfall works farther northward and persists longer, the higher end of the ranges could be met in more towns and the possibility will exist for some towns to exceed 12'', especially across southern Connecticut:

Accumulating Snows Likely Across Connecticut Wednesday, March 21st, 2018

Our active string of winter weather looks to continue as we are tracking yet the possibility for another accumulating snowfall event on Wednesday. Forecast models have been rather consistent over the past week on this possibility, however, there have been some inconsistencies with the exact track of the storm. Like the last storm, however, it appears that there will be a rather large gradient across the state with regards to snowfall totals which will make constructing a snowfall map rather difficult. Anyone who gets under intense banding will get the most snowfall accumulations while anyone who doesn't get under the banding may not see a whole lot in terms of accumulations. Where the banding sets-up will be key!!

Currently, there is energy moving into the state of California. This energy will continue progressing into the southern Plains over the next few days before strengthening as a developing shortwave trough amplifies across the Gulf Coast states:

There is also a current piece of vigorous shortwave energy over the central Plains with an associated area of surface low pressure. This piece of energy and surface low will continue slowly progressing eastward over the next few days. As the energy across California moves west and amplifies, it will interact with the piece of energy and surface low pressure over the eastern United States. When this process happens the surface low pressure and system as a whole will begin to rapidly strengthen as it works towards the east coast:

One feature to watch which could result in a storm track further south is a vigorous piece of shortwave energy which hangs around across southeastern Canada. While forecast models this morning are suggesting the possibility for a big hit of snow across portions of Connecticut we still have to watch how the forecast models handle this energy in southeastern Canada because it could easily suppress the system further south which would mean less in the way of snow:

Latest forecast models seem to be in rather strong agreement that this system is going to really strengthen just south of Long Island and this is evident by forecast models becoming vertically stacked with the system south of Long Island. We can see this by looking at the 925mb, 850mb, 700mb, and 500mb charts and tightly closed contours (indicating closed off low pressure centers) which develop south of Long Island. This placement of the closed lows is a prime location for a band of extremely heavy snowfall to set-up right over Connecticut:

Forecast models are suggesting excellent snow growth over Connecticut along with sufficient moisture within the snowgrowth zone and excellent upward vertical motion within the snowgrowth zone. The graphic below from this morning's run of the GFS forecast model is showing forecast omega values along with the dendritic snow growth zone. This is showing a deep snowgrowth zone with the -12C to -18C zone extending from about 600mb to 500mb and a period of rather high omega values indicating very strong upward vertical motion. This suggests there would be a period of extremely heavy snowfall, likely within a potent band. We need to watch where this band sets-up as this is where the highest snowfall totals will occur along with the heaviest snowfall rates:

Over the next 24 hours the details should begin to become much more clear and the forecast will be able to become much more fine tuned. Also, there is a very small possibility we could see a period of light to perhaps moderate snow across the extreme southern Connecticut beginning mid-to-late tomorrow afternoon. If this does occur there is a possibility of some spots picking up as much as 1-3'' of snowfall from this. I will have a forecast update tomorrow afternoon.

In addition to the likelihood for accumulating snows, winds could be rather strong too, especially across coastal Connecticut on Wednesday where winds could gust upwards of 50-60 mph. This coupled with fairly wet and heavy snow could lead to scattered power outages and tree damage. This potential needs to be monitored very closely as well.

 Below is what I am thinking...but keep in mind the 8-14'' zone is with regards to the banding. This zone, along with totals will be adjusted and fine tuned once it becomes more clear where the banding will set-up and how intense the banding will be:

Quick Thoughts on the Tuesday, March 2013, 2018 Snowstorm

One of the most unique aspects of weather is forecasting. Forecasting can be challenging, it can be difficult, it can feel nearly impossible at times, it can be stressful, but in the end it is fun! At least for myself, one of the most enjoyable aspects of forecasting (outside of trying to prepare my readers as best as possible for whatever mother nature has in store) is the learning that takes place during a storm and just after a storm. Every single weather event provides us with a different and unique set-up and each of these set-ups usually comes with surprises. For anyone who is a forecaster the one thing that we must understand and accept is that we will be wrong at times. If you can't accept this forecasting is probably not for you. There are two different types of people out there; there is the type who get very emotional and then lash out and criticism when they are wrong and there are people who take being wrong as a learning experience and they go back, re-evaluate the storm and try to find what they miss. For the forecasters in this second category, these are the ones who are on the path of success or on their way towards the path of success. 

This past storm (while still currently underway!) had numerous challenges from day one. As we drew closer to the storm, forecast models indicated we would likely be dealing with a scenario in which we could see two potentially heavy bands of snowfall across Connecticut which could dump a quite a bit of snow over some towns while areas in between these bands could struggle to accumulate much. When you have a scenario such as this, constructing and presenting a snowfall map becomes quite challenging and this is because snowfall totals are not really uniform across a large area and this leads to sharp and large snowfall gradients sometimes in just a span of a few miles! 

In my blog post from yesterday (http://weatherwiz.blogspot.com/2018/03/accumulating-snows-likely-overnight.html) I discussed the possibility of the two band scenario and discussed what impacts this could have. Well this scenario is exactly what unfolded. Below are a couple screen shots from the radar at 9:43 AM, 10:26 AM, and 1:08 PM. I've highlighted the heavy bands of snowfall:

Notice how elongated and how think/narrow they are. The narrowness of these bands is what makes constructing a snowfall map in these cases a challenge because you just don't know where they will set-up and you don't know how long they will sit in a particular area. In cases like this a difference of even 5 miles can mean the difference between like 4-5'' of snow and as much as 12...15...even 20'' of snow!!! I mean how do you reflect that in a snowfall map? 

Also discussed in the post from yesterday was the term subsidence and how anytime you have a heavy band of snow (sue to extreme upward vertical motion) you must have extreme downward motion (think of the all so popular phrase, "what goes up must go down"). It was discussed that you would have subsidence inbetween the two bands. While forecasting how much snow falls in the areas under the bands and how heavy the intensities are (snowfall rates per hour) is tough, forecasting what will happen in the areas of subsidence is another challenge in itself. In areas of subsidence it can still snow...it's typically very light and doesn't accumulate quickly but this helps to shape the very sharp gradients between a few miles. To give an indication on just how crazy some of the gradients are, here is a tweet sent out by award-winning and NBC Connecticut 's chief meteorologist, Ryan Hanrahan:

Just wild stuff! While forecasters struggle with how to visualize this in a forecast, this is why it's very important to listen to what a forecaster has to say. Often times, the forecaster will explain these situations and try to give as much detail as possible because it's just too difficult to provide this detail on a map. 

Perhaps in the future, as our technology improves and we continue to grow a better understanding of how these mesoscale bands work, we will get to a point where forecasters can confidently forecast exactly where a band (or bands) will set-up and snowfall maps can be constructed to point out where these highest totals will occur and what areas will see much less given subsidence. 

Accumulating Snows Likely Overnight into Tomorrow Across Connecticut

We are tracking yet another accumulating snowfall event later tonight into tomorrow and even at this stage there are still some uncertainties with regards to the exact track of the storm. This is just one factor which will determine just exactly how much snow we see across Connecticut and what type of snowfall totals we can expect. Part of the problem with these uncertainties too is in the end this will come down to mesoscale factors (which will be discussed below) and those are extremely difficult to pinpoint sometimes more than 6 hours out...they can even be difficult to do so just a few hours out.

One of, if not, the biggest key with regards to this system is how two pieces of energy will interact with each other. There are some differences within the forecast models on how these pieces of energies not only evolve but how they interact:

Energy #1 continues to dig towards the southeast through the Great Lakes region while energy #2 continues to dig southeast through the Tennessee Valley towards the east coast. Once energy #2 is off the coast of the Carolina's, it will then make a turn towards the northeast and this is when we begin to see the two pieces of energy begin to interact (or phase). This will lead to rapid cyclogenesis (strengthening) of a low pressure system just off the coast. This is where we are faced with some questions with the pieces of energy. There are differences within the forecast models regarding the strength of each of the pieces of energies and also with the handling of energy #2. The NAM forecast model evolution allows for the storm to get tugged in closer to the southern New England coast and also has a much larger precipitation shield.  The result is the potential for higher snowfall totals across much of the state. The GFS and European forecast models, however, are a bit farther southeast and have a much more compact (smaller) precipitation shield resulting in less snowfall potential for much of Connecticut.

This is just one piece of the puzzle, however, and there are other clues in place which I think helps to shape which direction to forecast in terms of snowfall across Connecticut. Unfortunately these clues don't tell us exactly where certain features will setup, just that these certain features will be a big player. These will be addressed below:

Rapid Storm Deepening/Storm Becoming Too Strong

Due to the interaction between the two pieces of energy mentioned above, we are going to see very rapid cyclogeneisis/strengthening of the surface low pressure occur. In fact, the system may become too strong too quickly. This can make snowfall forecasts very difficult because while you'll have some areas hit really hard, you'll have many areas struggling to accumulate. Think of tropical systems...what is one noticeable feature they have? If you answered banded precipitation as you work out and away from the storm's center you're correct! The thinking about this is such sharp pressure gradients help to shape and result in pockets of rapidly rising air...it is under these pockets where you would see the most intense and heaviest snowfall rates. However, because you have these areas of rapidly rising air, you also must have rapidly sinking areas of air. This results in extremely light snowfall rates and intensity. Where these areas set up is extremely difficult, if not impossible to pinpoint this far out. How does this make a snowfall forecast challenging? Let's see Hartford County as an example. Let's say the snowfall forecast for Hartford county was 8-12'' but we had some of these extremely heavy bands setup over parts of Hartford County and some areas were in between these bands. You would have some cities within the county likely fall within the 8-12'' range (and maybe even locally higher amounts) and you would have some cities receive much less than 8''. This just goes to illustrate how these bands can really complicate a forecast.

Frontogenesis/Subsidence 

This can somewhat be tied into the above paragraph, however, not all storms have banded like structure of the precipitation but most of these bigger storms do have areas where strong frontogenesis leads to extremely heavy bands of snowfall...we saw this exact case with this past storm) and outside of this frontogenesis you have subsidence. Frontogenesis is the strengthening of horizontal temperature gradient with height. This leads to very strong upward rising motion and heavy snowfall rates and intensity. Subsidence is the sinking motion of air and that results in much reduced snowfall rates and intensity. The NAM forecast model actually hints at the possibility of two bands of heavy snowfall to set up with subsidence right in between these two bands. The first band would be over western and portions of central Connecticut with the second band right along the Connecticut and Rhode Island border:

The GFS isn't too dissimilar from the NAM in that it also hints at the potential for two bands of extremely heavy snowfall. The exception is the GFS is a bit farther east with the second band and has it kind of setup over portions of far southeastern Massachusetts as opposed to back over the Connecticut/Rhode Island border:

The European forecast model has a nice zone of strong frontogenesis traverse right over the entire state of Connecticut. However, this could also be due to the resolution of the graphics of the source used to view the data and the resolution may not be good enough to sort of pick up what the NAM and GFS advertised. This is something which really makes constructing a snowfall map quite challenging and is a major reason as to why there will likely once again be "in-storm" updates.

Amount of Liquid Precipitation

The other question we face is just how much liquid equivalent is expected to fall across the state with this storm. As a general rule of thumb, 1'' of liquid equates to about 8-10'' of snow. However, this can vastly depend on snowfall ratios (how fluffy the snowfall is). The above, equates to 8:1 to 10:1 snowfall ratios (1 inch of liquid = 8-10'; of snow). If conditions warrant higher snowfall ratios, then 1'' of liquid can equate to as much as 15''+ of snow! In the case of this storm, it does appear ratios have a better chance of exceeding 10:1 and possibly as high as 13-15:1, however, this will largely depend on how great our snowgrowth is (we will explore this later). Forecast models generally are showing anywhere from around 0.50'' of liquid (western part of the state) to as much as almost 1.40'' across the eastern part of the state (NAM is much more pronounced with this. The GFS is generally 0.60'' to 0.70'' across the state while the Euro appears to be about 0.40'' west to near 1'' east:

After analyzing some bufkit soundings across the state we do have great snowgrowth (at least through late morning tomorrow) with sufficient moisture/ice within the snoowgrowth zone and upward vertical motion which indicates that there will be zones of great snowgrowth and fluffy snow flakes which should accumulate rather quickly. However, bufkit soundings also suggest what was mentioned a few paragraphs up and that is subsidence. Within the white box we see blue contours. These blue contours represent sinking motion (subsidence) while the red contours (highlighted in the red box) indicate rising motion. The blue contours within the snowgrowth zone are a strong signal for the potential for subsidence and reduced snowfall rates:

What can we expect?

• Flurries/light snows to begin breaking out between 12:00 AM and 3:00 AM tomorrow morning.
• Light to moderate snows will overspread portions of the state between 5:00 AM and 8:00 AM. 
• Between 8:00 AM and 1:00 PM will be the height of the storm. During this time snowfall intensities will range anywhere from light to perhaps heavy. Who sees heavy snows and light snows will all depend on how the precipitation is structured across the state and whether we are looking mainly at banded precipitation and are dealing with areas of subsidence. In the heaviest bands of snow, snowfall rates could approach 1.5'' per hour. 
• After 1:00 PM to 2:00 PM bufkit soundings show a decaying snowgrowth zone and the storm should be moving off to the north and east so snowfall will begin to wind down. 
• Below is what I am thinking, however, keep in mind this will LIKELY have to be refined once the processes described within this post better become better known and understood. 
  

Wednesday, March 7th, 2018 Snowfall Forecast Update

The forecast continues to be on track for a rather significant snowstorm across a large chunk of Connecticut tomorrow. Potential for mixing and a change to rain as you near southeastern Connecticut will keep snowfall amounts on the lower side here. There is even the possibility for mixing as far as north and west of Hartford. In addition to concerns about mixing of sleet and rain, there is also a big concern for the possibility of a rather extensive dry slot to push into central and eastern Connecticut late afternoon which could further hold back snowfall totals across these parts and there is the potential for frontolysis late afternoon as well. This process will be discussed later on.

Late yesterday afternoon and overnight, forecast guidance continued to come in extremely impressive for substantial snowfall totals for a large portion of Connecticut. This had me very tempted to increase snowfall totals with my afternoon update. However, while this morning's data continued being impressive, a few flags showed up which prevented me from raising totals. While I did slightly expand my 10-14'' zone slightly eastward, (I also did include the possibility for isolated amounts of 18'') I expanded the mixing line further to the north and west which resulted in lesser snows across these parts.

Today's data indicated a pretty sizeable westward storm track which not only would allow for warmer air both at the surface and aloft to work into a larger portion of the state but it also introduces the potential for a rather extensive dry slot to move into the state as well. Analyzing 700mb (~10,000' above the ground) relative humidity (RH) values on both the NAM and GFS forecast models we see RH values of less than 30% overspreading much of central and eastern Connecticut on the NAM with these values just to the south of Connecticut on the GFS. This is due in part to the 700mb low tracking overhead. As low pressures become very strong drier air is typically ingested into the storm in the mid and lower levels of the atmosphere and this happens typically to the south and east of the 700mb low track:

 
Both the NAM and GFS also indicate rather impressive 800mb-600mb vertically averaged frontogenesis across the entire state during the afternoon hours. This would be indicative of moderate to heavy snowfall across the majority of the state away from any areas mixing. Bufkit profiles also show excellent snowgrowth during the afternoon hours along with sufficient moisture within the snowgrowth zone (not shown) and very strong upward vertical velocities (indicated by the red contours) with omega values exceeding 50 units. All of this confirms that we will see moderate to heavy snows during the later morning hours through the majority of the afternoon. As a note the NAM is a bit more impressive than the GFS:

Both models also indicate the process of frontolysis happening late in the afternoon and early evening. This process is the opposite of frontogenesis. If frontogenesis is the strengthening of the horizontal temperature gradient with height (which strengthens upward vertical motion) frontolysis is the weakening of this horizontal temperature gradient with height. This processes reduces the degree of upward vertical motion. This is something which could result in a rapid lessening of snowfall intensity by late afternoon which is something that could result in the lower end of the snowfall forecast verifying as opposed to the higher end of the range:

A point-and-click forecast sounding for interior southwestern Connecticut shows a moist absolute unstable layer (MAUL) as well. This is a strong signal for not only extremely heavy snowfall but also suggests the possibility for thundersnow as well which would further increase snowfall intensities:

What to expect:

• Light snow begins to break out between 11:00 PM and 2:00 AM and remain quite light through mid-morning with some breaks during this time as well. 
• After 10:00 AM-11:00 AM the snow rapidly begins to increase in intensity with the heaviest snows occurring between this time and about 5:00-6:00 PM. During this time snowfall rates could approach 2-3'' per hour at times, especially in areas under the heaviest banding and the potential for thundersnow would exist as well. 
• After 6:00 PM the snow intensity may begin to taper down, especially if drier air moves in. 
• Light snows would then persist into the late evening/early overnight hours. We have to watch timeframe closely because if the dry slot does not work in we could be looking at much more snow, especially the central part of the state. We also need to watch and see if the heaviest banding sits and pivots over western Connecticut which would mean higher totals here. 
• While winds won't be as strong as Friday, gusts of 25-45 mph will be likely (strongest at coast) and this could yield near blizzard-like conditions at times along with isolated power outages. 

I may have another update tomorrow on snowfall totals once we know how the banding will transpire and whether or not the band will sit in place and then pivot or just move through. Here is my updated snowfall map:

Plowable Snows Likely Wednesday Across Connecticut

The weather pattern has certainly become much more active as we've entered the month of March and that trend will continue this upcoming week as there is continued growing confidence for plowable snowfall across the entire state of Connecticut this Wednesday. Computer forecast models have been in strong agreement for the past week on the possibility of a rather significant storm to impact the state o n Wednesday and that agreement continues. There is, however, some disagreement with regards to the exact track of the storm and this will ultimately affect exactly how much snow we see, where the heaviest banding/highest snowfall totals occur (and whether this happens to be somewhere in Connecticut), and where we see an area of subsidence which would mean reduced snowfall totals somewhere. Over the course of the next 24-36 hours these questions should be resolved.

We are watching two key pieces of energy which are expected to phase and once they phase the result will be the development and cyclogenesis (rapid strengthening) of a low pressure just off the coast of the Carolina's where surface convergence and upper-level divergence will be favored:

As the storm works up the coast there is some uncertainties with regards to exactly how close to Connecticut the storm tracks. Some of the forecast models track the storm farther off to the east. This result would mean the heaviest snows likely being confined to central and eastern Connecticut and also a reduced possibility for mixing along the southeast coast. Other forecast models are farther west with the track and this result would mean heavy snows across western and central Connecticut...perhaps even the heaviest occurring in eastern New York and northwestern Connecticut and a higher likelihood for mixing across southeastern Connecticut. These details will be ironed out over the next 24-36 hours.

Most forecast models develop an extremely potent storm with the potential for extreme upward vertical motion with this storm. This indicates that there will likely be a zone of extremely heavy and intense snowfall, the question just is where does that occur? This is the biggest question/challenge at hand with regards to snowfall forecast. We will examine below:

The NAM also indicates that the best frontogenesis (strengthening of horizontal temperature gradient with height) would remain west of Connecticut with frontolysis (weakening of horizontal temperature gradient with height) moving into Connecticut late afternoon and early evening. This indicates that the heaviest snowfall and most extreme rates would be just to the west of Connecticut:

However, prior to frontolysis and perhaps as the system works east and the best frontogenesis pivots through western Connecticut we could see some extremely heavy banding and very heavy snowfall rates per the NAM and this indicated very well by some bufkit soundings. This bufkit profile over Waterbury Connecticut yields two windows for extremely heavy snowfall; one during the midday and the second during the early portion of the evening as the system is beginning to depart. This profile shows a very favorable snowgrowth zone with impressive omega (red contours indicate upward vertical motion) penetrating the snowgrowth zone. One possible question here though is would moisture be lacking in this zone and this questions arises with less than 90% relative humidity values within the dendritic snowgwoth zone:

Using the same image but with relative humidity overlayed this shows relative humidity values less than 90% within the dendritic snowgrowth zone. Not a major problem but this could be something which inhibits excellent snowgrowth a bit:

The GFS also shows substantial lift within the snowgrowth zone and even hints at the possibility of some subsidence within the lower levels looking at a bufkit sounding from Waterbury, CT:

The GFS also advertises rather strong vertically averaged 800-600mb frontogenesis over the entire state during the afternoon, however, like the NAM the frontogenesis weakens and we see frontolysis develop. This indicates that as we approach the early evening snowfall intensities could weaken before finally picking back up briefly as the system departs:

So as of now what can we expect?

The details mentioned within this post are all critical to how much snow we see, where the heaviest banding/highest snowfall totals set up, and whether or not we see any areas of reduced snowfall totals thanks to subsidence or weakened upward vertical motion. As these details become ironed out the snowfall map can be adjusted to account for these details.

• Light snows begin to break out between 11:00 PM Tuesday night and 2:00 AM Wednesday morning. 
• Snowfall intensity begins to increase in intensity by late Wednesday morning with a period of moderate to very heavy snowfall lasting through mid afternoon. During this time snowfall rates could approach 2-3'' per hour in the areas which are under the heaviest banding. 
• Between mid-afternoon and late afternoon there is the possibility of reduced snowfall intensities. This is due to the strongest frontogenesis and upward vertical motion perhaps pushing west and north of the state. This will have to be watched because a prolonged duration of this phenomena could result in lesser snowfall totals for many locations. If we don't see reduced snowfall intensities during this time this would result in the likelihood for even higher snowfall totals across many locations. 
• As we near the height of the storm, strong gusty winds will begin to develop thanks to a strengthening pressure gradient across the region. Winds could gust as high as 25-45 mph with the higher gusts occurring near the coast. 
• As the system begins to depart the back edge of the storm will begin pushing through and there is the potential for this band to be extremely heavy which could add to some of the snowfall totals. This is something which will also influence the potential for higher end snowfall totals. 
• There is the likelihood for snow to mix with sleet and rain across southeastern Connecticut and this will result in lesser totals here. There is also the possibility for some mixing to occur across the majority of the state during periods of lesser intensity if the storm tracks further west and we get an influx of warmer air in the boundary layer. 
• Snow begins to wind down during the mid to late evening hours.

Below is my fist call snowfall map. Keep in mind that this will likely be adjusted tomorrow as the details mentioned above become more clear: