One climate cycle has received a lot of attention in the last few years. That's the El Nino/La Nina cycle, a variation between unusually warm and unusually cool waters in the tropical Pacific Ocean.

But there are other cycles that get less publicity but plenty of attention from meteorologists. One that impacts our area, especially in winter, is called the North Atlantic Oscillation - NAO for short. The NAO is based on pressure differences from north to south in the North Atlantic Ocean, approximately between the Azores Islands to the south and Iceland to the north. At one extreme of the NAO, called the Positive phase, air pressure is unusually high near the Azores, and unusually low near Iceland. This large pressure difference leads to a strong westerly jet stream blowing across the Atlantic. At the other extreme, called the Negative phase, the pressure difference is much less, so these upper-air winds tend to be weaker, and the jet stream pattern tends to have lots of dips and bends in it.

Now all this is happening out over the Atlantic Ocean. But with the East Coast of the U.S. just to the west, it's not much of a stretch to think that this cycle over the ocean can affect our weather. Well look at that tomorrow night.

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