Quick Hitting Storm to Bring Accumulating Snows 02/17/18-02/18/18

A quick hitting but potent storm system will bring plowable snow to the state of Connecticut overnight Saturday into Sunday morning. The snow is expected to begin mid-to-late evening, however, the snow should be cleared out by 7:00 AM Sunday morning.

A potent piece of shortwave energy propagating through the northern branch of the jet stream will interact with shortwave energy moving through the southern branch of the jet stream. Associated with the southern stream piece of shortwave energy will be an area of surface low pressure. As the shortwave associated with the northern stream continues to amplify (strengthening) and interact with the southern stream shortwave, the result will be for further strengthening of the low pressure system as it begins to pass south of Long Island. One question we still face is how far south of Long Island the system tracks as this will ultimately dictate if the heaviest of the snowfall pushes into Connecticut or not:

While this will be a rather fast moving system, there are numerous indications we will see a period of moderate to heavy snows work into the state in which snowfall rates could approach 1.5'' per hour. Forecast models indicate that a period of intense upward vertical motion will move over the state during the overnight hours on Saturday. It is during this period when we would see the heaviest snowfall intensities and snowfall rates:

Forecast soundings indicate we will have excellent snowgrowth potential with good upward vertical motion within the snowgrowth zone and plenty of moisture. This is how you get the production of dendrites which are the snowflakes which accumulate quickly. This bufkit profile sounding from the latest run of the NAM forecast model for Windsor Locks, CT shows excellent snowgrowth and decent omega within the snowgrowth zone:

While perhaps not a true MAUL (Moist Absolute Unstable Layer) some forecast soundings indicate some fairly unstable layers within the troposphere. This could act to further enhance upward vertical motion and snowfall rates:

Based on the above (along with several other factors) the thinking is for a several hour period of moderate to heavy snows to overspread the state during the overnight hours. With a marginal southerly component to the surface winds, this could lead to some mixing issues across the immediate shoreline which may reduce snowfall totals here. Across the northwestern part of the state totals may be reduced due to being just a bit too far northwest of the heaviest snows. Below is what to expect:

• Snow begins between 7:00 PM and 9:00 PM Saturday evening. 
• Snow quickly begins to increase in intensities with the heaviest snowfall rates occurring between 11:00 PM Saturday and 4:00 AM Sunday. 
• During the peak, snowfall rates could approach 1.5'' per hour. 
• Snowfall begins to wind down by 5:00 AM Sunday and will be cleared out by 7:00 AM Sunday. Some leftover flurries may remain across eastern CT.