Sunday, January 7, 2024 southern New England Winter Storm

 Our first widespread, accumulating snowfall event of the season is upon us! Snow lovers were starved after pretty much a shutout (some places did get some snow) during the month of December. If you happened to read my winter outlook, I mentioned January and February were going to be active and we are off to those races! Anyways, let's get right into all the fun science and meteorological applications and thought process behind the forecast.

Synopsis

A frontal system moving across the Gulf Coast states Friday lifts northeast across the mid-Atlantic region during the day Saturday. An area of surface low pressure develops within the mid-Atlantic and strengthens as it lifts northeast off the mid-Atlantic coast and passing south and east of Long Island:

Discussion

As the low moves over the open waters, this is where the fun begins! Thanks to the temperature gradient which exists between the water and land this time of year, combined with the jet stream dynamics, the surface low will begin to strengthen. As the surface low strengthens and the circulation elongates we'll see a low pressure center develop about 5,000 feet above the ground. Thanks to a strong latitude horizontal gradient, this will help to strengthen this low pressure circulation as the system is passing northeast south of Long Island.:

This track of the 850mb low, combined with the fact that it will be strengthening places a good portion of southern New England in a very favorable spot for an intense band of snow to traverse. This is indicated very well assessing 850mb frontogenesis on both the GFS (left) and NAM (right) forecast models:

Several forecast soundings across the region all show good cross hair signature (when maximum lift bisects the snow growth zone). When/where this is occurring, snowfall rates will be heaviest, snow growth will be best, and snow ratios will be highest. We'll look at a few examples below:

This system will also have a copious amount of moisture to work with. Forecast model guidance develops 50+ knots of easterly inflow at 850mb, throwing a great deal of moisture into a cold low-level airmass. The result will be plenty of snowflakes developing:

While we're well within the 48-hour window of start time, there remain a quite a bit of uncertainties within our forecast model guidance. This has become an increasingly annoying theme the past few years. There are differences with the overall track and speed of development. Some forecast models are on the more amped side, resulting in a farther north and west track and development. This introduces warmer air into southern areas and would also result in the greatest frontogenesis and subsequent banding shifting farther north. This would also increase potential for subsidence in southern areas. 

Forecast 

• The highest totals should be confined to interior east-central Massachusetts into southern New Hampshire, and southwestern Maine. This is where snowfall ratios should be the greatest throughout the duration of the storm and where the intense banding is likely to persist the longest. In fact, there may be a swath of snowfall of 12-16 inches within this zone!
• Towards southern Connecticut. snow ratios will be held back due to some warmer air in the lower levels, just above the surface. Snowfall ratios improve briefly as the intense banding lifts north. 
• Easterly surface winds off the warmer water will hold back accumulations greatly across extreme coastal Connecticut, southern Rhode Island, and far eastern Massachusetts. 
• Snow will also be on the wet side across southern Connecticut into interior southeast Massachusetts. This could result in isolated downed tree limbs and power outages. 
• Snow begins Saturday evening (between 7:00 PM-10:00 PM from southwest to northeast), with intensity quickly picking up through the evening. 
• The worst of the storm is between 11:00 PM - 5:00 AM, however, for northeastern areas this will be extended through much of Sunday morning. 
• Light snow lingers through much of Sunday with moderate to at times, heavy snow across interior northeast Massachusetts. 

Below is my snowfall forecast: