17 October 2012
Notice how incredibly warm the Northwest Atlantic ocean is now. The warmth stretches well northward to Greenland, and out into the North Atlantic as well. Now look at the 500 millibar height anomalies for September. (The 500 millibar pressure level is about 6 km above the surface and a warmer atmosphere pushes this level higher) The height anomalies are directly related to the warmth of the atmosphere.
Notice here how the warm oceans are producing a warm atmosphere over the North Atlantic, and also in other areas. If you live in the Mid-Atlantic or Northeast, you are probably thinking it was a cool September compared to normal, and you can see why looking at the anomalies. The warm oceans pushed the heights up over the Atlantic and the NE Pacific, leaving a trough of cooler air over the Great Lakes and Northeast U.S. When it comes to weather, the ocean is more than just the elephant in the room, the ocean IS the room.
When a large winter time high pressure develops over Greenland, major changes happen to North American weather. This pattern is called a negative North Atlantic Oscillation (NAO) and tends to steer cold air from the Arctic into the Eastern USA. In 2010 a strongly negative NAO ,and an El Nino ,brought the “snowmageddon” winter to the East Coast. A Negative NAO greatly amplifies the weather pattern making the winds aloft blow more north and south than east-west.
Missing Arctic Ice
Recent research also indicates the loss of Arctic sea ice is also causing the overall storm track to amplify. In other words the ridges get stronger and the troughs get deeper. If we see this happen in the coming winter months, and the 500 millibar pattern remains basically as it has been over the last 6 weeks, we may be in for a rather cold winter in the NE U.S. El Nino could play a role, but it now seems that we may have a very weak event this winter or perhaps none at all. So there are a lot of uncertainties, but with ocean waters so incredibly warm in the North Atlantic, it will be a very interesting winter!
That warm ocean has also produced the warmest September on record. From NOAA today:
- The average combined global land and ocean surface temperature for September 2012 tied with 2005 as the warmest September on record, at 0.67°C (1.21°F) above the 20th century average of 15.0°C (59.0°F). Records began in 1880.
- The globally-averaged land surface temperature for September 2012 was the third warmest September on record, at 1.02°C (1.84°F) above average. The globally-averaged ocean surface temperature tied with 1997 as the second warmest September on record, at 0.54°C (0.97°F) above average.