Pattern in the northern Atlantic key to winter storms

Over the past few weeks I’ve been beating the drum about the important impacts that the Pacific can have on the weather pattern in New Jersey.  This week though, there is another body of water we need to monitor, and that’s the northwestern Atlantic.

While the Pacific does have a major influence on the weather patterns across North America and naturally New Jersey, there is an extremely important weather pattern in the northern Atlantic that influences the storm tracks for the winter storms in central New Jersey and really much of the eastern United States.  That feature is called the North Atlantic Oscillation.  

The North Atlantic Oscillation is like a stop light for disturbances in the jet stream.  When the stop light is green or positive, upper level disturbances and surface features move west to east at a progressive rate, which means that storms are typically harder to develop.  However, when that traffic light goes to yellow (transition) and red (negative), then major winter storms can develop along the East coast because the whole pattern can slow down.

There are several factors that go into determining the state of the North Atlantic Oscillation (NAO) including sea surface temperature gradient over the northwestern Atlantic and also temperatures in the stratosphere.  For this discussion, I’ll limit the mathematical and intense physics equations, however here are some basic rules.  

One, when the Atlantic is warm or exhibits above normal sea surface temperature anomalies, the potential for a negative NAO pattern is far greater because the temperature gradient from the warmer central Atlantic and colder northern Atlantic is far greater.  This thermal gradient leads to stronger storms.  

Two, the warmer the stratosphere is, the better chance there is for high latitude blocking.  Basically, think of the stratosphere like an air conditioner.  When the stratosphere warms, the stratosphere expands.  Well, the stratosphere, which is above the troposphere (where we live), can’t expand into space so the stratosphere presses down on the troposphere.  This leads to the troposphere cooling, which leads to stronger thermal gradients in the northern latitudes and thus a higher potential for storms.

So why is the state of the NAO so important?  

When the NAO changes states or is negative, an upper level low or a strong storm is located to the east of the Canadian Maritimes or about 50N/50W.  Now, when this occurs, a strong ridge or high pressure system develops over Greenland and northeastern Canada.  This pattern develop is our stop light.  Disturbances over the central and eastern United States have to slow down and they can’t move northeast towards the Canadian Maritimes because the pattern is blocked up.  As such, these disturbances take an alternate route, which leads to low pressure systems redeveloping along the East coast.  This pattern also leads to higher pressure over portions of the St. Lawrence River Valley (southeastern Ontario and southwestern Quebec) and New England, which keeps cold air locked in along the East coast.  As a result, the negative NAO pattern supports the development of major winter storms along the East coast and specifically for central New Jersey.  Of course, if the NAO is too negative, this can lead to the storm track being suppressed even further to the south which can produce major winter storms for the southern Mid Atlantic like the Washington, D.C. metropolitan areas while leaving many children and even some adults very disappointed and rather cold in central New Jersey.  

Now, when the NAO is positive, the traffic light is green!  This means that disturbances over the central and eastern United States are able to progress quickly from the Plains to the Canadian Maritimes with no other atmospheric features slowing down the pattern.  As a result, there is no reason for a low pressure system to redevelop along the East coast.  This type of pattern is typically quiet and leads to warm temperatures for central New Jersey.  

So as you can see, one of the key factors in determining the type of winter that central New Jersey will have is the development of the weather pattern in the Northern Atlantic.  When the NAO goes negative, many locations in central New Jersey are in for a bumpy ride!