As I head to bed for a few hours the first model of the night moves the projected path further west. I had concerns about this earlier Monday. If this trend continues look for the new map to double totals. Still not a major snow event for Boston, but plowable for sure. More by 6AM.
Tonight meteorologists and weather enthusiasts are quite excited in anticipation of the development of the big ocean storm which will form tomorrow. You may be wondering what the big deal is about a storm that is more of a miss for Boston than a hit. You are certainly justified in this thinking. However, let me put the size of the storm in perspective.
When we evaluate storms, one of the ways we note the strength of a low pressure center is by its pressure. Storms exist to balance the atmosphere. Their purpose is to mix cold and warm air and try to achieve equilibrium. When a large difference in temperature exists and energy from the jet stream rides over this contrast, storms often develop.
Air rises in storms and as the air leaves the planet, the pressure lowers. The wind you feel is the air rushing into the storm trying to fill the void being created by its very existence. If the storm is really large, the air can’t fill the void fast enough and the pressure continues to fall. It's like trying to fill a swimming pool with a big hole using a garden hose, the water level keeps falling because what's leaving is more than what you are putting back. The faster the pressure drops the more wind we experience. Those winds are attempting to balance the rising air.
Normally, on an average day, the pressure of the air above you exerts about 1013 millibars of pressure. In a typical strong storm, this pressure can fall to 980 millibars. At that level of pressure, a storm would generate a considerable amount of wind and precipitation. The faster the pressure falls each hour, during a storms development, the greater the intensity.
When a storm loses 24 millibars of pressure in a day the storm is said to have undergone bombogenisis. In layman’s terms, this is akin to the atmosphere exploding a storm in a very short period of time. During the upcoming situation the pressure is forecast to drop 30 millibars in one day. This will create a storm in the ocean with a pressure typically seen in a category three hurricane.
According to Ryan Maue at WeatherBell Analytics,other notable March nor'easters will very low pressures are: 957 millibars Mar 8, 1969 ,959 millibars Mar 18, 1981 and 963 millibars Mar 18 1976. The storm tomorrow is forecast to eventually become lower than all of those!
Low pressure isn’t the only factor in why a storm produces a lot of wind. If there is a big high pressure system a few hundred miles away, this generates even more wind. In the upcoming situation there will be a high, with a pressure of 1030 millibars in Canada.
The reason I spent so much time with this explanation is because I want you to understand the scope of this storm. While the heaviest precipitation will fall over the outer part of Cape Cod, far eastern Maine and Nova Scotia, the wind field is enormous and has the potential to be damaging.
I don’t like what if scenarios because they bring nothing to the table. That said, some of you might be thinking what if the storm came closer to the coastline? The reality is the storm would have to move nearly 200 miles further west than predicted and this isn't likely at this point. IF however it did, we would be looking at a damaging nor’easter with 1 to 2 feet of snow, widespread power outages and an all around very bad situation. As much as I love a good storm, this isn't one I want to come any closer.
The main threat from this storm is the wind, not snow. This is especially true over Cape Cod and the Islands where the blizzard watch is posted. To punctuate the strength of the storm, note the hurricane force wind warning just off our coastline. The blizzard is possible from all the snow being whipped around by the wind and making it impossible to see.
The Tuesday evening commute won’t be an issue, but the one Wednesday morning may be a bit slow. Early Wednesday, over Cape Cod, where the heaviest snow bands set up travel could be impossible much of the day. Snow will begin in Boston around 2 or 3 AM and not last long. This is why amounts are lighter in the city. There is some other energy moving eastward into the storm and will likely give the western part of the area some light snow up to an inch.
The storm will move quickly and the reason snow ends early in the Boston area. I believe it ends before the commute is over and around noon over the outer portion of Cape Cod. These times will be tweaked a bit during the day Tuesday. The map below is the same map from earlier Monday. I will likely change a few things Tuesday once I review the overnight models. I could increase the amounts over the outer part of the Cape, but I want to see some more data first. Check back often for changes to the forecast which is still somewhat fluid. I may forecast Boston with 2 or 3 more inches than forecast after the new data arrives.
Here's my latest map
As I wrote, the wind is the big issue from this storm. While some parts of Cape Cod will exceed 8 inches or more of snow, it’s the near hurricane force gusts just offshore that are the big story. Even in Boston, winds will be strong enough to cause scattered power outages. However, winds do not appear to be forecast at a level to cause widespread power issues off Cape Cod.
If you live over Cape Cod and the Island and even southeastern Massachusetts or extreme south eastern Rhode Island, I recommend preparing for power loss. If it doesn’t happen, consider it a good thing.
Once the storm passes, it remains chilly and windy Thursday before we turn milder for the end of the week and the start of the weekend. Many of us will see mid 50s or even 60F for Friday! Bye bye snow. I’ll have much later Tuesday and during the evening as the snow develops.
I’ll be updating the forecast on Twitter @growingwisdom.
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