Major Winter Storm Likely for Northwest Hills of Connecticut late Thursday night and Friday (12.16.2022)

We are very close to a significant winter storm for the majority of Connecticut outside of the coast, however, it appears the pieces just won't come together for that to happen with the exception of northwest Connecticut. 

The forecast weather pattern for Thursday evening features a very large closed upper-level low pressure system over the upper-Midwest region embedded within a longwave trough. Along the southern periphery of this upper-level low, embedded within the jet stream, will be several vorticity maxima's. Our area of focus (highlighted in purple box) is vorticity which is curling poleward towards our region:

As we now look at the 500mb jet stream and stick to the purple highlighted box, we see a very favorable region of surface convergence and upper-level divergence which will net the development and strengthening of a secondary low pressure right along the mid-Atlantic coast. As the system strengthens low pressures will also form aloft:

So why isn't the whole state getting snow? While we have cold air in place ahead of the storm and a supply of cold air to the north, unfortunately where the storm is strengthening and how the strengthening occurs will result in a surge of warmer air moving into much of the state. Due to the storm track colder air may remain locked in across the northwestern part of the state, keeping all precipitation in the form of snow.

As cyclogenesis occurs close the coast (and just inland) a strong easterly flow will develop within the lower-levels of the troposphere and at the surface. Unfortunately, since we are on the eastern side of this development, we'll see an easterly flow become established across the state which will yield an influx of warmer marine air:

The biggest question we still currently face is, where does this low pressure and resultant mid-level low pressure track? If the track was more northeast or even a bit more east-northeast, we would turn the wind direction across the state to more northeast to north-northeast and would lock colder air in place and that would give a predominately statewide snow event. However, guidance continues to suggest the low pressure will track more north-northeast. This will keep the majority of the state in a warmer east-northeast wind direction, with the exception being the northwest hills. 

Forecast models indicate that intense lift will be traversing the state Thursday night and the first half of Friday with the first wave of intense lift moving into the state during the early overnight. It is very possible that under the most intense lift, the northern half of Connecticut could see a period of heavy, wet snow with large flakes. Where the temperature profile is favorable in northwest Connecticut, this will yield very heavy and wet snow:

18z/14 NAM bufkit sounding from northwest Connecticut shows this intense lift described above with over 40 units of omega within the dendritic snowgrowth zone for a period overnight Thursday. This would result in a period of extremely heavy snowfall with rates upwards of 2-3'' per hour:

So what can we expect?

• Precipitation begins to move into the state Thursday evening. Across the northern part of the state, precipitation may be a rain/snow mix, however, late evening and early overnight when stronger lift traverses the state, this may yield a few hour period of heavy went snow. 
• Any areas with mixing will changeover to rain as warmer air filters in and the degree of lift weakens. 
• The northwest hills should remain all snow for this event, however, there could be some mixing during any lulls of precipitation when lift is weaker.
• Precipitation begins to wind down Friday evening and as colder air filters in on the backside the majority of the state (with the exception of the shoreline) could end as some snow with maybe an inch or two of accumulation.
• It will also be on the gusty side with sustained winds 10-20 mph with gusts 25-30 across the state.
• Isolated power outages possible across northwest Connecticut due to the wet nature of the snow.

Below is my current forecast: