Storm Bringing Rain, Ice & Snow Incoming to New England

New England's next system will approach later today and into tomorrow. This will be a frontal system with a primary low lifting well north of New England. A secondary low is poised to lift through northern New England, making this system an inside runner. Winter weather advisories are in effect for much of northern New England away from the coast. Winter storm watches across northern Maine have been downgraded to winter weather advisories.

Trends over the past couple days have pointed to a weaker storm system that is quicker moving. The system will likely arrive in western New England Saturday evening. The storm will steadily spread eastward through the rest of Saturday night before peaking for most early Sunday morning. The storm now looks progressive enough that it may be largely pushing out of New England through Sunday morning. Spot showers and flurries will be possible behind the system's cold front.

Below: HRRR showing potential weather this evening (1st image) and in the pre-dawn hours Sunday (2nd image):

Maine, being the farthest east, will naturally hang onto the storm the longest heading toward the daylight hours on Sunday. The storm will likely be undergoing some form of cyclogenesis as it moves east of New England. This would allow wrap-around snow to linger longer across eastern Maine. The precipitation across eastern Maine is more likely to be snow rather than a mix or rain.

The secondary low's track has trended a bit farther south over the past 24 hours, which does increase the odds of a snowstorm across eastern Maine as colder air gets locked in. The storm, which will have been moving quickly across New England, will slow down and strengthen once it exits eastern Maine, allowing for some lingering wrap-around precipitation and windy conditions.

Below: HRRR showing potential weather around Sunrise Sunday (1st image) and early afternoon Sunday (2nd image):

There will likely be cold air at the surface when precipitation begins to arrive early Sunday morning. This will come as the system lifts its warm front across New England, allowing warmer air to ride over the colder air at the surface. This is a prime setup for a rather messy storm across northern New England with a period of snow, sleet, freezing rain and plain rain all possible. The earlier arrival of the storm compared to how it was looking several days ago means it will struggle to cool off enough for any kind of frozen precipitation.

Exact precipitation types and amounts will be determined by the secondary low's strength and exact track. Not only has the track trended farther south, but the system has also trended weaker overall. Both of these favor cooler temperatures and lighter precipitation. This situation is becoming more likely as guidance has been trending toward cooler temperatures over the past 36 to 48 hours. What this may do is allow for a longer period of a wintry mix over interior northern New England. With that said, precipitation would also be generally lighter with a weaker storm system.

With a warm front overrunning cold air at the surface during the overnight hours, it will likely set up a cold air damming situation. Cold air damming occurs when a low-level cold air mass basically gets trapped by the mountains. With a warm nose of air rising aloft, it can lead to a period of freezing rain with warm air across the mid-levels and cold air remaining at the lower levels.

This allows for sleet and/or freezing rain to fall instead of snow or plain rain. The issue with cold air damming is that models tend to have a "warm bias", meaning they tend to push the colder air out too fast. Cold air in these situations are often stubborn and slower to scour out than guidance often suggests.

Below: Diagram of cold air damming:

Given the expected setup, the most dominant wintry precipitation looks to be freezing rain rather than sleet. This will come as warm air moves into New England aloft with colder air staying at the surface initially. This will likely be a deep layer of warmer air, and with colder air at the surface getting scoured out, freezing rain is expected to win out over sleet for most.

Freezing rain accretions of a glaze to a tenth of an inch are possible, with the highest amounts across Vermont, where isolated 0.2-0.4" amounts are possible. Probabilities for any icing outside of a very quick glaze across southern New England and near the northern New England coast are slim. The storm will generally be colder in Maine, and central Maine is where mixing may end up being more by way of sleet. Far north New Hampshire and Maine remain likely to see mostly snow.

As the storm strengthens and slides southward into the eastern Gulf of Maine, colder air will likely get locked in for northern Maine. This will also allow for a period of heavier precipitation, allowing for decent snow accumulations. With such a progressive storm, snowfall amounts still look to remain in check, with 2-5 inches for most across northernmost New Hampshire and Maine. Northern Aroostook County will be the jackpot zone, which will stand the best chance at seeing a half foot or more as the storm remains all snow, slows down and strengthens nearby.

Also, on the backside of the system, colder air will wrap around and upslope snow will be likely across the higher terrain of northern New England. This would likely occur later Sunday and into Monday morning. This should help tack on some snow accumulations to areas that didn't see much at the onset Saturday night, especially across the northern Green Mountains.

Below: HRRR showing potential weather Sunday evening, with terrain-based snow continuing:

The other issue will be the potential for high wind gusts on the other side of the cold front. Winds will likely pick up rather quickly once precipitation begins to move out. Widespread gusts of 30-40mph are likely. Temperatures will also be dropping during this time, so the wind will have a bit of a bite on Sunday. Winds will stay elevated on Monday and upslope mountain snow showers will likely continue as well. After this system, New England will likely see a break in storm systems with the next one arriving next Friday or Saturday.