A rather potent frontal system sitting to the west of New England will drive its warm front through the region from south to north today. This frontal boundary has been stalled near New England's south coast, which has played a role in the region's dense fog this morning. This fog will be scoured out as the front moves northward. A period of warm air advection showers will occur as the front moves through the region. The main core of this frontal system will push through New England later tonight into Monday.
Overall, Sunday will be mostly dry for a majority of New England. The only real, organized shower chance will come with the light band of showers along the warm front. Other than that band, areas of drizzle will be around for much of the day and it will remain rather dreary and raw feeling all day. The freezing rain threat has been diminishing over the past 24 hours and little by way of ice is expected across Maine as temperatures continue to rise faster than what has been advertised over the past few days.
Below: HRRR showing potential weather early this afternoon (1st image) and this evening (2nd image):
The main round of rain will come with the system's cold front, which will be pulled through New England from west to east early Monday morning (western areas) through Monday evening (eastern Maine). This will come as the main storm system, which is potent, moves northward across the Great Lakes and eventually well north of New England.
Healthy convergence and strong forcing along the cold front will likely allow for a fine line of convection to develop across southern New England in the pre-dawn hours Monday. This line will continue to push north and east as the morning wears on. This line will contain heavy rain at times and a majority of rainfall will come during this relatively brief (couple hour) window when the line is moving through. Farther north, a period of moderate rain is expected with heavier downpours at times.
Below: HRRR showing potential weather around sunrise Monday (1st image) and around midday (2nd image):
Overall, rainfall amounts have been trending downward as the window of heavier rainfall has narrowed. This storm/cold front has also trended more progressive, leading to less time overall in the rain. A widespread half inch to inch of rain is expected for a large swath of New England, with lesser amounts (a quarter to half inch) across the northern tier and near the coastline.
With the reduction in rainfall amounts, the flooding threat has continued to lessen (and it was never very high to begin with). A majority of the rainfall above will come in a 2-3 hour window on Monday. Despite the heavy rainfall and potential for downpours, the fast-moving nature of the system should preclude flash flooding concerns. The current threshold for flash flooding to occur is 1.5 to 2.5 inches for most of New England, so total amounts around an inch will not cause these issues.
Across northern New England, there will be snowmelt adding to the precipitation totals. Around a half an inch to an inch of additional water is expected to melt out of the snow. The good news is that the snowpack is still very cold and is not ripe and not ready to melt down rapidly. While the valleys of northern New England will likely lose all of their snow, the mountain slopes and summits will likely hold onto some of it. With a reduction in rainfall totals, runoff from snowmelt isn't expected to be much of an issue.
Below: Forecast snowmelt:
This system will have a strong southerly low-level jet. This jet will allow for the increase in temperature as it will contain winds of 70-80mph. Despite this strong jet, winds aren't expected to be much of an issue at the surface. A strong inversion (when a layer of warmer air aloft sits over a layer of colder air at the surface) will prevent truly impactful winds from making it to the surface. Gusts of 30-45mph will be possible. Higher elevations and the coastal plain will stand the best chance to see gusts on the higher end of the scale.
Winds may become their most gusty during the convective line of downpours, leading to a windswept rain for a couple hours, but again, the winds overall don't look like much of a threat. Just how high wind gusts can get will be dependent on how much the inversion can erode with the surface warming. Areas that push into the 50s will have the best chance to see gustier winds.
Below: Diagram of an inversion. This inversion will be strong, which will act as a barrier for the strongest winds, filtering out the strongest gusts and leaving the surface with much weaker winds than what could have been:
After a brief break on Tuesday, New England's next strong system will move through the region Tuesday night into Wednesday. A coastal storm system will likely form near the Mid-Atlantic before strengthening and tracking near New England. As of now, this system looks to track well inside the benchmark. This track, along with the lack of preceding cold air, will result in a rain event for southern New England and the northern New England coastal plain with the chance for snow or mixing well inland across northern New England.
Without any cold air in place, it will take the storm creating its own cold air to produce frozen precipitation across interior northern New England. Naturally, this will be most likely across the mountains with chances diminishing as you get closer to the coast. The storm's final track will determine just how expansive snowfall is across northern New England. A track closer to Cape Cod would allow for snow to spread across much of northern New England away from the coast while a track farther inland would push the rainfall farther north.
Below: Current likelihood of impactful winter weather Wednesday morning to Thursday morning:
With the current thinking, there is a chance for several inches of accumulation across interior northern New England, especially in the mountains. Just how far south and close to the coast this accumulating snow can get remains the biggest question mark. Should a secondary low form and strengthen along the system's triple point (where a warm, cold and occluded front meet) in the Gulf of Maine, that would be a major help in producing more widespread snow. There remains large differences in opinion among guidance.
Below: Model roundup (Euro, GFS, CMC and ICON) for New Year's Day:
Typical post-storm snow showers will be possible in the mountains throughout Thursday regardless of how the bulk of the system ends up laying out. The end of this week looks to feature much colder weather than the start of it. Overall, the first half of January will likely feature cold temperatures for the entire east coast.
The question naturally gravitates toward if any storms will be able to take advantage of the colder weather and bring snow. Conditions look mainly dry for late next week and into the start of the weekend. Heading toward the end of next weekend into the start of next week may get interesting. The large-scale setup will favor a storm system sliding across the country. What this storm does when it reaches the coast will need to be watched. Should a coastal low develop, we'll watch the track of it to see if New England can get a snowstorm or not.
This is a reminder not to put all faith in what models are showing right now. Over a week away, we can only accurately look at the big picture. Details on timing, track, intensity, precipitation type and all of that information will come with time. For now, we'll focus on what's right in front of us this week.
Below: Current weather map for next Sunday (January 5):
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