A nor'easter will be moving over New England beginning late Monday night through Tuesday evening. Latest guidance has taken a rather notable southward shift this morning. The storm's center is still looking to pass near the 40/70 benchmark. The storm will rapidly strengthen as it passes New England. Explosive cyclogenesis is looking more likely. The storm's central pressure will likely be in the 970-980mb range as it passes New England. The storm complex is currently over the southeast, creating severe weather and flooding today.
The overall setup for the storm will involve a primary low tracking up the Appalachian Mountains and into the Mid-Atlantic early Tuesday morning. As it does so, a secondary low will form off the Mid-Atlantic coast and strengthen as the primary low weakens. The southward shift in guidance does two things: leads to less mixing and more snow at the onset in southern areas and pushes the highest snowfall amounts southward.
ALERTS
TIMING
The southward shift in guidance has led to a later start time all around. Snow will likely break out across Connecticut and Rhode Island around midnight. Snow will spread quickly northeast until all of southern New England is seeing snow by sunrise. Snow will spread into southern New Hampshire and Vermont by sunrise to mid-morning. Mixing will likely be confined to the south coast and Cape Cod.
Expected weather around sunrise Tuesday:
The peak of the storm will likely be mid-morning through early afternoon. At this time, snowfall rates across southern New England will likely be around the 1-2 inch an hour mark with some snowfall bands potentially going up toward 3 inches an hour. This time will feature increased wind gusts bringing near white-out conditions at times. As the storm rapidly intensifies, it will be able to force cold air down to the surface from the upper levels.
Expected weather early afternoon Tuesday:
Snow will likely continue through the afternoon with snowfall rates gradually winding down around mid-afternoon from west to east. The storm is a quick hitter and will be pulling away by Tuesday evening. While snow showers will likely continue, especially for eastern Massachusetts and southeast New Hampshire into the evening, the bulk of the accumulations will be over.
Expected weather Tuesday late afternoon to early evening:
SNOWFALL
As stated before, latest guidance has shifted the storm a bit further to the south. This is a deviation from how things have played out so far this winter, which was to continually trend the storm northward leading up to the event. This has led to snowfall amounts being pushed southward. Areas near the coast in southern New England are a bit of a wild card with rain and mixing at the onset potentially holding back snowfall amounts.
A wide swath of 8-12 inches continues to look likely across much of southern New England. The jackpot zone is currently looking to set up over southern Worcester County and into northern Rhode Island and northeast Connecticut. These areas will stand the best chance at seeing up to a foot of snow. This storm will be very moisture-rich and will allow snowfall rates of 1-3 inches an hour. Thundersnow is not out of the question as the storm rapidly intensifies.
From mid-morning through about mid-afternoon, whiteout conditions will be possible and blizzard conditions will be possible across eastern Massachusetts where winds will be the strongest. Snow will generally be the wet and heavy kind with large, fat flakes falling. This will further help reduce visibilities.
While some guidance continues to point toward localized amounts of over a foot across portions of southern New England, we opted not to include a 12-18 inch zone on our map this morning. This is because the speed at which the storm is moving as well as the fact that the wet, heavy snow type is more difficult to accumulate. At this point, we think 12 inches is the high point on snow, but we'll have one more map update this evening.
Probability of snowfall reaching at least 12 inches (percentages drop significantly when going up to 18 inches):
There will be a sharp northerly cutoff in snowfall when getting into northern New England. At this point, we still see 6+ inches falling in southern New Hampshire, but amounts will likely drop off quickly heading further north amid dry air. We need to watch today's trends closely as further southward shifts will lower amounts even more. There is growing bust potential for all in northern New England.
Bust potential in southern New England stems from how quickly the storm is moving. With the storm trending toward a later onset time, snow amounts may be lower. At this point, bust potential in southern New England is much lower than northern New England as continued southward trends would still leave Massachusetts, Connecticut and Rhode Island in the steady to heavy snow.
POWER OUTAGES
With marginal temperatures hovering around the freezing mark, this will likely be a heavy, wet snow for most. This is the kind of snow that sticks to everything. When you begin talking about the potential for 6-12 inches of this type of snow, some tree branches and power lines may come down.
Combine this fact with gusty winds of 30-40mph and there will likely be scattered power outages across southern New England. We still don't expect a major outage event, but there is growing concern for scattered outages across southern New England. Overall, the southward shift in guidance has led to the outage concern being pushed south.
WIND
Widespread strong winds will not be a major concern with this storm. Gusts may reach 50-60mph on Cape Cod for a couple hours on Tuesday. Elsewhere, gusts will generally remain below impactful levels. The only caveat is that heavy, wet snow sticking to the branches will only be stressed further by any gusts.
With frequent gusts around 40+mph and heavy snow falling that will reduce visibility, a blizzard is certainly possible on Cape Cod. Official blizzard criteria are as follows: sustained winds or frequent gusts of at least 35mph and reduced visibility to a quarter mile or less for at least three consecutive hours. That is certainly possible on Cape Cod and the south shore. The question will be if snowfall rates are heavy enough to reduce visibility and if the conditions can last three hours. It will be something to watch.
COASTAL FLOODING
The main threat of coastal flooding will be along the eastern Massachusetts coast through Portland, Maine. While astronomical high tides will be on the downward trend, they will still be high on Tuesday. Combine this with a 2-3 feet surge and widespread minor coastal flooding is likely.
The highest threat for moderate coastal flooding will be from Boston Harbor south to Cape Cod. Basically, the threat for coastal flooding grows the further south you go in New England to Cape Cod (Rhode Island and Connecticut will not see issues).
Expected wind direction and speed Tuesday afternoon:
As usual, the extent of coastal flooding will come down to precise timing between when the maximum surge will be and high tide. The Tuesday afternoon high tide is the biggest concern as the storm center will likely be passing Cape Cod at this time. Moderate beach erosion will be a large concern as New England's coast has taken a beating this winter.
Tide forecast for Boston Harbor. Other coastal areas from Portland, Maine to Provincetown, Massachusetts are forecast well into minor flood stage with some bordering moderate flood stage:
The southward shift in the storm lowers the coastal flood threat from the Massachusetts north shore through Portland. Still, elevated tides along with a surge and building waves from the storm is still enough for a coastal flood watch to be posted as minor flooding remains likely with pockets of low-end moderate flooding not out of the question for northern Massachusetts and New Hampshire.
As for expected impacts: "Numerous roads may be closed. Low lying property including homes, businesses, and some critical infrastructure may be inundated. Some shoreline erosion may occur."