A frontal system will bring a period of light rain and snow showers to New England later Saturday into Sunday morning. Light accumulations of both rain (0.10-0.25") and snow (1-3" in mountains) are likely. This system's cold front will slow down as it reaches New England's coastline for Sunday into Sunday night. A wave of low pressure will quickly develop later Sunday along the slowed front and track northeastward near New England, allowing for a period of steady snow across a wide swath of the region.
ALERTS
This storm is shaping up to be on the border between winter weather advisory and winter storm warning. Watches will be upgraded or downgraded within the next 12-24 hours.
TIMING
Snow, and possibly rain along the coast, will likely begin to break out across southwestern New England around mid to late afternoon Sunday. The storm will steadily move northeast, lifting its shield of precipitation northeast across New England at a decent clip. By the early evening, snow will likely have spread across all of southern and central New England and begin pushing into coastal Maine.
Below: NAM showing potential weather around mid-afternoon Sunday (1st image) and early evening (2nd image):
By the middle of the night, the storm will likely make its closest pass to New England. This is when snow will be the most widespread across New England and the heaviest snowfall rates occur. Should a favorable setup occur, there could be a brief window of 1-2" an hour snowfall rates across interior southern New England and the northern New England coastal plain (the setup will be discussed below).
Below: NAM showing potential weather just after midnight:
The storm is very progressive and will be racing up the coast through the morning. Snow will likely quickly begin to break up from southwest to northeast during the pre-dawn hours. By sunrise, a bulk of the snow will be centered over Maine. Snow will continue to break up in Maine through the morning with all of New England cold and dry by the afternoon. The sun may even begin to come out by sunrise in southern New England.
Below: NAM showing potential weather around sunrise Monday:
SNOWFALL
There remains a decently large spread in tracks that are being depicted. These tracks range from the low passing over Cape Cod to near the benchmark. The closer the storm tracks to Cape Cod, the stronger it would be, allowing for heavier snowfall rates across the interior of southern and central New England. This would also allow milder air into the storm, with more mixing and rainfall issues near the coast, keeping snowfall lower along the coastal plain. A track closer to the benchmark would allow for snow just about everywhere, but lighter snowfall overall as the storm would be weaker.
For the past couple days, we've been leaning toward a middle ground between these two scenarios, where the storm tracks offshore, but still inside the benchmark. This would bring a wide swath of 4-8 inches of snow across interior southern New England, southern New Hampshire and near the coast of Maine. Amounts would steadily drop off heading northward. Amounts would also drop heading south and east, toward Cape Cod.
The fact that there remains such a wide spread at this stage is a red flag for snow totals. The track of this storm was always going to have the biggest impact on snowfall. This is why we have that little disclaimer on the snowfall map above. Guidance also differs on where the best lift will be for heavier snowfall rates and how much moisture will be available for the storm.
No matter how it ends up sliced, central and western Massachusetts, southern New Hampshire and coastal Maine, particularly Downeast Maine, will have the best chance to come away with the most snow. These areas currently have up to a 50% chance of seeing at least 6". The northern third of New England (due to being far removed from the storm center) and the South Shore (due to initial rainfall and mixing) will come away with the least.
Below: Current probability of seeing at least 6 inches of snow:
How intense snowfall rates are able to become may come down to whether or not a closed low pressure system is able to form. A closed low is a traditional, organized storm that has a fully enclosed center of circulation. These are more impactful and capable of heavier precipitation. Should the low pressure remain more of an open wave without a distinct center, snowfall rates would be more mild.
This isn't a traditional setup for a closed mid-level. With that said, one could form as the storm continues to move northeastward. This is why a secondary 5-8" zone is seen on the snowfall map above as the system will have more time to organize as it reaches for Downeast Maine. A closed low-level low would support a brief period of frontogenesis and high snowfall rates and snow banding across interior southern New England and southern New Hampshire. This is what would produce 1-2 an hour rates mentioned in the timing section.
The overall setup of this system is known as anafrontal. When most cold fronts cross New England, they advect cooler and drier air into the region, allowing precipitation chances to diminish (this setup is known as katafrontal). When an anafrontal setup occurs, the cold air rapidly pushes against the warmer air ahead of the front, causing the warmer air to rise over the colder air behind the front, resulting in clouds and precipitation behind the front rather than clearing. This is not a traditional setup for a nor'easter and not conducive for an overly powerful one.
The main limiting factor for snowfall will be the storm's quick motion. This is shaping up to be a 12 hour storm system for New England. This will help to hold snowfall in check. The main factor working for higher snowfall will be high snow ratios. For most, this will likely be a fluffier snow. This type of snow accumulates quickly as it compresses little on impact with the ground.
BUST POTENTIAL
The main bust potential will come from the clear track issues. Should the storm remain well offshore, it would be weaker with lighter snow totals. Also, if the storm remains an open wave throughout instead of developing a closed low, this would result in lighter snowfall rates, keeping snowfall down. With the quick motion of the storm, a closed low would need to develop early and quickly. The quick motion of the storm is also a limiting factor for snow totals regardless of how strong the storm is able to get. Bust potential is decently high with this one.
OTHER IMPACTS
One last quick note to make about this storm is that it will be one-dimensional. The storm will bring a period of steady to locally heavy snow, and that's just about it. No heavy rains, no damaging winds, no coastal flooding, no sleet/ice and low power outage potential.
ARCTIC BLAST
The Arctic blast of air coming next week will likely peak (or bottom out) early to mid-week. This blast will likely be deep and widespread across the central and eastern United States. For New England, the lowest temperatures appear poised to come in the Tuesday to Wednesday time frame. These days will likely see high temperatures in the single digits north to teens south.
Overnight lows will be in the single digits, on either side of zero. There will be a chance the coldest hollows of northern New England (mountains, Northeast Kingdom and northern Maine) will drop into the -10s. Wind chills will drop below zero during this time region-wide with minimum values potentially reaching for the -15 to -25° range.
BEYOND
Looking at the long term, a southern stream storm system appears poised to develop around early to mid next week near the Gulf of Mexico. This could bring the south another winter storm next week. Where this storm goes from the south remains up in the air at this point.
Whether or not it hugs the coast and comes up to the northeast or remains well offshore will likely come down to the timing of the Arctic air. A quicker departure of the arctic air would allow a window where the storm could sneak into the region late next week. A majority of guidance keeps the storm to the south, but it will be worth keeping an eye on in the coming days.
Below: Current Weather Prediction Center probability of impactful winter weather next Friday (January 24):
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