Light Snow Event Saturday, December 9th, 2017

Over the past several days computer forecast guidance has hinted at the potential for some snow showers or even some light snows across parts of the state in the Friday to Saturday timeframe. While there has been a great deal of inconsistencies with the operational forecast models as to how far west offshore moisture would track, computer forecast ensembles have painted a different story hinting that the likelihood for a far enough westward displacement of this moisture to impact at least portions of CT. Throughout the day today, computer forecast guidance has continued to track a bit westward with some of this moisture, increasing the likelihood for a period of light snows across much of the state during the day on Saturday. While a significant event is expected, some areas could potentially pick up as much as 2-3'' of snow.

Computer forecast models show two key areas of energy which may interact on Saturday. The first is some energy which is going to rotate around the polar vortex.  The second is an elongated area of energy which stretches up and down the eastern seaboard. Another area of focus is an impressive swath of moisture which extends from near Bermuda, through the southern tier of the United States into Mexico!

There also exists a stalled front off the east coast (this is the cold front which passed through here late Wednesday ushering in much colder air):

Latest guidance suggests this frontal boundary will retrograde back west over the next few days and this sets the stage for the likelihood of light snows during the day on Saturday. What happens is multiple areas of weak low pressures will develop within the elongated area of energy across the east coast and ride up along the stalled frontal boundary. What will help bring this moisture west is an impressive and amplifying (strengthening) 500mb jet streak. As this amplifies, this will help to tug the moisture off-shore west into CT and this will give us the light snows on Saturday:

Bufkit model data does show excellent snowgrowth.  You want the snowgrowth zone to be between 12,000 ft and 18,000' with the -15°C line intersecting it. In order to maximize and utilize the snowgrowth you want substantial moisture (relative humidity values > 90-95%) within the snowgrowth zone and excellent vertical upward lift. Using a bufkit sounding from Windham, CT does show sufficient enough lift within the snowgrowth zone for a period of light snow (in fact this would be pretty close to perhaps a brief period of moderate snow):

With this said, this is what I am expecting:

• Snow (snow showers to light snow) begins to break out across the state between 7:00 AM and 9:00 AM) Saturday morning.
• Light to even moderate bursts of snow (especially eastern CT) will continue through early to mid-afternoon. 
• Snow tappers off late afternoon.
• Expect slow travel during the event.

At this time, this is what I am currently thinking: