What Is A 'Greenland Block'? And How Could It Lead To Some Weird New England Weather Ahead?

An area of high pressure is developing in the northern Atlantic Ocean, an example of a “Greenland blocking” pattern that could increase the chance of a Northeast storm this winter, if it happens again later.

What is “Greenland blocking”? It's an area of relatively high pressure near Greenland which then blocks other large-scale weather features such as fronts and other storm systems from their normal west-to-east path.

This pattern is associated with the negative phase of the North Atlantic Oscillation (NAO), an index monitoring large-scale circulation patterns in the North Atlantic.

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How it typically influences U.S. weather: This pattern’s main method of manipulating United States weather is by causing the polar jet stream to take a sharp, southward plunge over the eastern U.S.

This can pull cold air from Canada into the eastern U.S. and also instigate East Coast snowstorms.

The northward-bound section of the jet stream can line itself up roughly with the Eastern Seaboard, dragging low-pressure systems up the coast causing snow, rain, wind and coastal flooding instead of allowing the systems to meander out to sea.

What's on deck for the Northeast: I​n this case, we're not talking about a winter storm with heavy snow.

A low will hitch a ride with the polar jet this week, taking a circuitous route from just offshore the mid-Atlantic coast eastward into the Central Atlantic and then northwestward toward New England and Atlantic Canada.

A bit of rain (and possibly wet snow for the highest elevations) is possible in parts of New England starting Friday as the low pivots back toward the region.

We could see déjà vu late this weekend into early next week as another system is expected to take a similar path, though it’s still too early to tell if any impacts will be felt on land.

U​nfortunately, this forecast isn't expected to provide much relief from the drought plaguing the region. Any precipitation should be light and relatively short-lived.

What this means for the winter ahead: Unlike El Niño, the NAO and Greenland blocking patterns tend to operate on a timescale of weeks rather than months, so we can’t say for sure how many such blocking patterns will form or how intense they will be this winter.

Sara Tonks is a content meteorologist with weather.com and has a bachelors and a masters degree from Georgia Tech in Earth and Atmospheric Sciences along with a masters degree from Unity Environmental University in Marine Science.