Brief Meteorological Background:
The below image shows the 500mb level (chart on the left) and sea-level pressure (chart on the right). These two images come from today's 12z run of the GFS and there are 3 highlighted areas;
1. This area is what is responsible for the development of the low pressure. Strong energy associated with the mid-level trough is leading to the development of the surface low which you can see in the chart on the right where the 3rd highlighted area is.
2. This highlighted area is a weaker piece of energy embedded in the northern stream moving into the northern-tier of the country. This energy will sort of combine with the southern stream energy, or "phase" and this will help the coastal storm to become a little bit stronger and also keep it a bit closer to the coast.
3. This highlighted area is the surface low pressure.
We will now fast-forward and look 24-hours down the road and the projected 500mb pattern and sea-level pressure chart:
1. With the first highlighted area, we can now see the trough and associated energy draped right along the east coast now. The trough here has a negatively-tilted component to it and this is something that will also favor the storm track to be closer to the coast.
2. The second highlighted area is our surface low pressure or our coastal storm. The system here is shown stronger than what it was just 24-hours prior and the system will continue to strengthen throughout the day on Saturday as it passes just to our south and east.
3. For the third highlighted area there is a blue circle here. One thing to notice is the lack of a surface high pressure in and around this region. Having an area of surface high pressure in this general region is a great way to keep colder air in the lower levels locked in place and this high can also prevent a storm track too close to the coast. Unfortunately, with no high pressure here and a storm track just off the coast, this will allow for warmer air to work in both at the surface and within the lowest 10,000ft of the atmosphere and that will be the reason why for multiple precipitation types.
With all this said what can we expect?
Forecast:
- Everyone will start off as snowfall with precipitation breaking out across the state between 4:00 AM and 6:00 AM with southern portions of the state beginning closer to 4:00 AM. While there is a big of dry air in place aloft, forecast soundings indicate the airmass should begin to saturate rather quickly.
- As the morning progresses snowfall will begin to fall more moderately to heavy at times. Snowfall rates may approach as much as 1'' to 1.5'' per hour at times during the heaviest bursts of snow.
- As the morning also progresses and the system works its way northward, warmer air will begin to work in the state in the lowest 10,000ft of the atmosphere. As this warmer air work in, precipitation across the state will begin to transition over from snow to sleet, freezing rain, and even rain, especially across southeastern CT. While some freezing rain is expected this is not expected to be a major issue, however, there may be enough to provide a coating of glaze across some communities.
- The system is expected to be a quick mover with the precipitation begin to wind down during the later half of the afternoon and be out by 7:00 PM, however, some light precipitation may linger, especially across the northeastern portion of the state.
- The heaviest of the precipitation will fall between about 12:00 PM noon and 4:00 PM. Much of the snowfall accumulations, however, should occur prior to noon as this is when we will begin to see the changeover process occur.
- The highest snowfall totals should be confined to the northwest hills and northeastern CT where cold air may stay in place a bit longer.
- Anyone traveling should take it extremely slow and expect numerous delays. Travel is not advised unless absolutely necessary.
Below is the projected snowfall forecast:
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