North Atlantic Oscillation: Large and in charge!

Written by: Bob Metcalfe

If you got a chance to catch our Winter 2008-2009 forecast, you may have seen a graphic talking about the "North Atlantic Oscillation" during that segment. Day-to-day weather is just one of the aspects we meteorologists look at, but often times to get a greater grasp on the weather "pattern" as a whole... we look at the bigger picture. Basically, we want to know if say over the next few days it will be on average colder or warmer than where we should be when compared to climatology. Compare this to an uptrend or downtrend in the stock market. Most know not to buy long when the markets are tanking (see October 2008.)

The North Atlantic Oscillation deals with what we call blocking patterns over you guessed it, the North Atlantic. We look to the vicinity of Greenland and Iceland and what we do is determine what the pressure trend is like several miles above the earth's surface. Why do this? Well this has huge implications on what the jet stream is allowed to do. If you clock your pipes what happens? The normal flow of water is impeded and you get a back up. In fact, my bathroom sink is doing this right now, and it almost overflows by the time I'm done shaving. The NAO is somewhat related. If you have a big high pressure parked in the north Atlantic, it backs up the typical west-to-east flow of things in the northern hemisphere, and the net result is USUALLY a cold weather pattern that develops over the east coast (meaning us!). Replace this with a low pressure, and our weather is allowed to flow like normal, resulting in typical temperatures values. Also, the NAO is most effective as a tool during our winter months versus the summer.

Right now, we have a strongly negative NAO, which would correlate to our temperatures being below average for the most part. Looking at the current forecast, we'll loosely stay at or below the norms for about the next week. But again, this is just one piece of the puzzle.