New England's next storm coming this weekend will involve an area of low pressure that will lift northward from the Ohio Valley to the north and west of New England. A secondary low pressure system will form and track near New England's coastline. Overall, trends have been toward a later developing secondary low and a stronger primary low. This continues to support and raise confidence about mixing taking over the snow from south to north Sunday morning. The northern tier will still likely see mostly snow.
The main storm system will eject out of the Rocky Mountains today and dive southward into the Tennessee Valley on Saturday. In the south, the storm system will pick up plenty of Gulf moisture, providing the basis for heavier precipitation rates. Precipitable water values look to be as much as 300% above normal for southern New England on Sunday. This (southern stream) system will begin to interact with northern stream energy near the Great Lakes by Saturday afternoon.
Below: Euro showing potential weather early Saturday afternoon:
This interaction will allow precipitation to break out in New England by late afternoon. Snow showers will initially begin over Connecticut and western Massachusetts first before spreading north and east through the evening hours Saturday. Snow will initially be lighter and more scattered in nature before filling in as the center of the main storm system approaches. There will be plenty of cold air at the start of the storm for snow to fall everywhere. Pockets of moderate snow will be possible across southern New England as forcing along the warm front increases.
This approaching warm front will advect warmer air into the mid-levels from south to north through Sunday morning. This will create a transition to a wintry mix from south to north. This looks to begin very early Sunday morning for New England's south coast, likely around 1-2am. As the mid-levels continue to warm from the primary low pressure system, this mix line will gradually work its way northward throughout the early morning into sunrise Sunday.
The latest trends have the mix/snow line draped across northern Massachusetts by sunrise. The speed at which this line actually moves will be dependent on the strength of the primary low and the development of the secondary low. This will need to be watched in real-time. As the inland nature of the low pressure system continues to send milder air into the region, a transition to plain rain will likely be underway at this time for southern New England's coastline.
High resolution models, just now coming into view, show the cold at the surface being stubborn and slow to erode away. This isn't surprising as cold air damming in this setup is typically difficult to move out. Guidance often shows this layer of cold air getting pushed out too quickly versus what actually happens. In reality, cold air at the surface is trapped and will take time to move out. With that said, the warm nose of air aloft will likely be quite strong. This will likely result in mixed precipitation lasting for much of Sunday morning across southern New England.
Areas that may see mixed precipitation for a majority of the event will be the higher terrain of southern New England (Worcester Hills, Berkshires). The exact rate of a switchover to plain rain from freezing rain and sleet will (again) need to be watched as it unfolds. Across much of northern New England, outside of maybe southern New Hampshire, snow will continue falling. With a strengthening storm and a developing coastal low, snowfall rates may increase.
Through the afternoon, a battle between milder air aloft and cold at the surface will be well underway across southern and central New England. The exact northern extent of mixing versus mainly snow will be decided by various factors during this time frame. Mesoscale models remain at odds over the northern extent of the mix/snow line.
The NAM is currently a warmer scenario with the mix line making it well north into the White Mountains and much of Vermont. RGEM is much colder, with the line failing to make it past southern Vermont, the New Hampshire Lakes Region and Maine's coastal plain. With the stubborn nature of cold air damming, we're leaning more toward the colder end rather than the warmer end.
Below: NAM vs RGEM early Sunday afternoon:
This is a long-duration storm that will be ongoing through all of Sunday and into Sunday night for New England. Both the rain and mixing lines will likely reach their northern extents by Sunday evening. Exactly where this will be is hard to say given the spread and uncertainty surrounding precipitation types in the afternoon. The northern tier of New England, including much interior Maine, will likely be cold enough for all snow from start to finish. These areas could see a significant snowfall.
Total snowfall in areas that see mainly snow will have the chance to see at least eight inches of snow. The northern tier of New England will likely see 10-16 inches at this point. The biggest wild card in snowfall will, of course, be the speed and northern extent of a changeover. Southern New England will stand to see a general 2-5 inches of snow.
The main reservations about southern New England totals will be the fact that the front end thump of snow will not be overly intense. Snowfall during much of this time may feature very small flakes, similar to last weekend's storm. The nature of these flakes has led to snowfall coming in on the lower end of ranges or under-performing entirely across southern New England in the past couple snow events.
The other main area to watch will be for the potential of freezing rain and icing. At this point, impactful icing appears to be on the lower end of the spectrum. With that said, there are decently high probabilities of at least a tenth of an inch across interior southern New England with at least a glaze possible across all of southern and central New England. This threat is a large wild card, and the threat level could increase or decrease over the next 24 hours. With some wind and heavier snow, scattered power outages may be possible.
Below: Current probability of at least a tenth of an inch of ice:
As stated before, this is a long duration storm (very unlike many of our storms this season). It will likely take until Sunday night to start shutting everything off for much of New England. Much of Maine along with the Green and White Mountains, could see snow showers through Monday morning. A couple of these snow showers could sink farther south on Monday. Monday will be windy and cold. Next week will feature persistently cold temperatures with a potential storm to watch around the latter part of the week. There are no thaws in the picture at this time.
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