Accumulating Snows Possible Thursday into Friday

We aren't looking at a major snow event Thursday night into Friday but portions of the state could see some light snowfall accumulations as an area of low pressure develops along a cold front just to the south and east of CT. As has been the case this winter this is a bit of a tricky forecast, however, there are some signals that we could see a band of moderate snow develop and traverse over the portions of the state. While this window may be rather brief there is the possibility for a brief period of moderate to perhaps heavy snows. Given the timing of this potential, this could have an impact on the Friday morning commute.

As we move towards the end of the week and amplifying (strengthening) long-wave trough will approach our region along with an attendant cold front. Within the amplifying trough will be strengthening shortwave energy. This strengthening shortwave energy will help to enhance mid-level forcing and lift across the state along with aiding in the development of a weak area of surface low pressure along the cold front:

While computer forecast models aren't particularly impressive with their output of liquid precipitation totals, there are some signals this could be a bit underdone. We will explore some of these signals below.

One signal is with regards to a blob of warmer than average sea-surface temperatures just east of New Jersey and south of Long Island and the very cold low level airmass which will work into the region as the trough begins to push through:

What is the significance of this? When you have such a cold airmass pushing over waters which are much warmer this creates atmospheric instability due to the large temperature gradient which exists between the water temperature and temperature of the airmass. This works to enhance upward vertical motion. This is one driver in the development of lake effect snows. This may also explain why some of the "smaller" forecasted events thus far this season have overperformed, especially closer to the coast where the effects of this enhanced gradient is stronger. The warmer water temperatures can also add increased moisture and water vapor for a system to work with, especially if the system tracks right over these warmer waters.

The second signals is an enhanced area of frontogenesis and vertical velocities which some computer forecast models indicate will develop across portions of CT, particularly east of the CT River. Frontogenesis, simply defined is the increase in horizontal temperature gradient over time. The stronger the frontogenesis, the stronger the horizontal temperature gradient which indicates a steep temperature change as you ascend through the vertical in the atmosphere. This is another feature which can enhance the degree of upward vertical motion. Vertical velocity is a measure of upward vertical motion with the greater the value the stronger the upward vertical motion:

A bufkit sounding from this morning's run of the GFS computer forecast model over Windham, CT suggests the potential for a window of moderate snow Friday morning. Bufkit soundings show the snowgrowth zone between 12,000 and 18,000 ft (preferred zone for the generation of excellent snowgrowth) with sufficient moisture (not shown here as it would complicate the picture) within the snowgrowth zone along with sufficient upward vertical motion:

What should we expect?

As we move through this evening a warm front will be approaching and as it approaches we will run the risk for a few snow or rain showers. During the day on Thursday temperatures will warm a bit and we will continue to run the risk for a few showers. Late Thursday afternoon and evening the cold front will approach and then eventually push through and usher in colder air. At this time, this is when computer forecast models suggest the development of a very weak area of surface low pressure along the front which was described above. At this time we will begin to see the blossoming of some precipitation which should be in the form of some snow as the surface temperature begins to drop towards the wet-bulb. The timeframe of snow should be between 3:00 AM and 9:00 AM Friday morning where periods of light to even moderate (at times) snow will occur. Given the timing, there could be some impact to Friday morning travel. Based on the above this is what I'm thinking right now: