It was a beautiful Sunday across Southern New England with plenty of sunshine, light winds, and seasonably cool temperatures. It was a good day to consider how you will prepare and manage through our upcoming nor’easter.
This is a very complicated weather system that is approaching. The computer guidance we all use to help us forecast does not handle volatile situations well. This is because when the weather becomes more extraordinary it’s at the fringe of the mathematics within the models to be able to accurately predict the future atmosphere.
But based on past situations that are similar, we can make some reasonable assumptions as to what’s going to happen Monday night through Wednesday. Small deviations by just 20 miles in the rain/snow line will have a big impact on how much will snow will be on the ground where you are.
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The storm will intensify off the southern New England coast Monday night and slowly meander out to sea by Wednesday. In the big picture, rain will begin Monday evening and will end as snow Wednesday morning.
The upper level winds that carry storms are going to become cut off from the main jet stream. Think of it as if a river that is flowing and you come to a whirlpool where you spin for a little while before moving again — that’s what’s going to happen with the approaching storm and why it will last so long.
This also means that colder air will be able to work into the system while precipitation is still falling. This will change the initial rain over to snow from the northwest toward the southeast on Tuesday and Tuesday evening.
Those areas that change first will have a major snow storm while those areas that change over at the end of the storm will have much less snow.
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The map below shows a change to snow on Tuesday from west to east. The precipitation will be coming down hard enough Tuesday afternoon and evening that the snow will accumulate even on roads. Look for heavy, wet snow that can create power outages in areas that receive over 4 inches.
If there’s a change earlier, the gradient on this map will be pushed east. If the change is delayed, the lower snowfall totals will be pushed west.
Most of the accumulation in Boston will occur Tuesday night, and the precipitation will come to an end on Wednesday morning. Because it will be night, the snow will have an easier time accumulating. I expect the biggest impact from the snow to be Tuesday afternoon through Wednesday morning.
Obviously areas that receive just a little bit of snow will not have much impact to roads or travel. There will be delays at both Logan Airport and ferry service during the height of the storm Tuesday night and Wednesday morning. Power outages can also occur from both heavy snow and strong winds.
Wind is another factor in this upcoming nor’easter. The strongest winds will occur Tuesday through early Wednesday. The loop below shows the strongest wind gusts along the coastline where a high wind watch is posted. Notice those winds move north along the coastline and then head out to sea. Inland areas will have the least amount of wind but they still can get power outages because of the heavy, wet snow and wind combination.
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Where it is all rain, there will be a lot of it, anywhere from one inch to perhaps as much as three inches of water. This can create street flooding as well as basement flooding, and it’s a good idea to check your sump pumps.
I’m not expecting much in the way of coastal flooding with this nor’easter. The tides are not astronomically high and therefore the predicted flooding is in the minor range as you can see from the selected tide predictions below.
It’s back to sunshine for Thursday with temperatures into the 40s and significant melting of whatever snow is on the ground. Power will be coming back online during the day for those who have lost it and things will quickly be back to normal.