This incoming system will involve a primary low tracking to the north of New England with a secondary low forming near southern New England. The interaction between this system and a trough entering the region from the Great Lakes will allow the storm to deepen, leading to a period of moderate rain and snow.
The track of the secondary low is likely to move the system directly over southern New England. This will allow mild air to advect into much of New England, leading to a mainly rain event for southern New England and the lower elevations of northern New England. Snow, or a rain/snow mix, will be seen across the foothills and mountains. Warm air from a southeast flow will likely warm temperatures through Saturday night with the rain/snow line pushing northward as the night goes on.
ALERTS
TIMING
Dry air over New England should help to slow the arrival of precipitation. Precipitation will start in the afternoon in western areas. In the evening, precipitation will quickly spread from southwest to northeast Precipitation will be rain in lower elevations and snow in higher elevations.
Expected weather around 8pm this evening:
The bulk of the storm for much of New England will occur during the overnight hours as the storm strengthens. With a southerly flow for much of New England, the rain/snow will get pushed north (and from lower elevation to higher elevation) as the night goes on. There is the potential for heavy snowfall rates where the snow lingers.
Expected weather early Sunday morning:
The storm is initially pretty progressive, so it will be moving along quickly on Sunday. Much of southern New England will likely begin to dry out starting in around mid-morning as it moves in. The bulk of the storm will gradually come to an end from south to north across northern New England during the daylight hours. Maine will naturally stay in it the longest, with precipitation lasting through the afternoon and shutting down from east to west.
Expected weather around sunrise Sunday (1st image) and around early-afternoon Sunday (2nd image):
The system will slow down and linger around in the Canadian Maritimes after exiting New England. This will allow upslope snow showers to continue across the mountains and northern Maine through Monday morning. This could add an additional few inches of snow onto the mountains from Sunday afternoon through Monday afternoon.
Expected weather Monday morning:
SNOWFALL
Snowfall amounts will likely be highly variable from location to location in northern New England. Elevation will play a significant role in totals, with valley towns likely seeing much less than the slopes of the mountains. Overall, snowfall has trended upwards across the Green Mountains as the primary, northern low pressure has trended weaker, allowing colder air to linger longer. Only minor changes have been made to the snowfall map elsewhere.
The White Mountains will likely be the jackpot zone, with up to a foot of snow possible on the mountains themselves. Areas below 1,500 feet are more likely to end up at or below 8 inches. A period of heavy snowfall rates up to an inch an hour will be possible across the Green and White Mountains early Sunday morning. Areas that see upwards of 6 inches will have power outage issues with the heavy, wet snow clinging to branches.
The river valleys of northern New England, the Mount Washington Valley and the Great North Woods will likely see a period of snow before mixing with or changing to rain, keeping amounts lower. The key with snowfall will be where the cold air can hang around the longest. We know it will hang with the mountains, the question is how low in elevation will the snow persist?
There is large bust potential with this storm. This comes from multiple aspects. First, snow will be heavy and wet, which suppresses, making it more difficult to pile up. Second, snow will have trouble sticking initially in areas that have a bare ground. Third will be how aggressive the rain/snow line gets. Fourth, temperatures will also be marginal, a degree or two could be the difference between rain and a large haul of snow.
All of this could lead to a busted snowfall. With variable snowfall rates, some areas will see less than others. Should heavy snowfall rates be able to develop, it will help cancel out some of these issues. These late season snowfalls that are elevation dependent always come with a degree of uncertainty.
Another aspect in the snowfall is that upslope snow showers will persist through Monday morning. This could add several inches in places Sunday evening through Monday afternoon.
In southern New England, the Berkshires and possibly the northern Worcester Hills could see a couple inches of snow before the transition to rain.
RAINFALL
A widespread half inch to inch and a half of rain is possible Sunday morning across southern and central New England. While some of the smaller streams have had time to recede, some of the larger streams and rivers remain elevated from a wet week. With saturated top soils and frost remaining underneath, it could lead to rapid runoff.
Areas farther north that still have a snowpack will also see snowmelt contribute to runoff. While notable flooding is not expected, minor issues could arise and isolated flash floods are possible where the storm will be rain from start to finish. This threat is greater in northern areas where the precipitation will last longer. The main threat for issues will be for rivers and streams to once again rise out of their banks, similar to what occurred on Thursday.
COASTAL FLOODING
The progression of the winds have sped up over the past 24 hours. This has decreased the coastal flooding threat for southern New England. Still, minor coastal flooding remains likely from Narragansett Bay through the North Shore as tides will be astronomically very high. A coastal flood advisory has been posted for southern New England (minus Connecticut). A coastal flood watch is in effect for Narragansett Bay, Caped Cod and the South Shore.
More notable coastal flooding remains a possibility for northern New England. Minor coastal flooding with pockets of moderate coastal flooding is likely. Hampton, NH and Portland, ME remain forecast to reach moderate flood stage. Portland's forecast is for a tide of 13.7 feet, which would be another top to highest tide set this winter.
Wind direction and speed in the late-morning:
In northern New England, numerous roads may be closed. Low lying property including homes, businesses, and some critical infrastructure may be inundated. Some shoreline erosion may occur, especially after the beating the northern New England coast has taken this winter.
A coastal flood advisory is in effect for the New Hampshire Seacoast through Maine's Midcoast. A coastal flood watch is in effect for Downeast Maine. These alerts have been shifting around, and likely change again this afternoon. It is curious that the National Weather Service downgraded the coastal flood watch to an advisory for New Hampshire and southern Maine rather than waiting to upgrade to a warning. This may change later today.
Tidal forecasts for Narragansett Bay, RI (1st); Hampton, NH (2nd) and Portland, ME (3rd):
WIND
A strong low-level jet will move over New England Saturday night, however, a strong inversion will likely prevent the worst of the winds from reaching the ground. While the winds on their own wouldn't normally cause much of an issue, the wind combined with heavy, wet snow in areas will likely lead to power outages in the mountains. Coastal areas could also see outages from the wind alone where gusts of 50-60mph will occur.
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